Basic to Site Specific Electric Training

Basic to Site Specific
Electric Training
Create by: Theunis Venter

Safety:
• No job is so important, that
• Low / High voltages can cause electrical shock, burns and death.
• Do isolation procedure on power before proceeding with any work on
electrical equipment. This procedure should be read in conjunction with
the following documents: ASSESSMENTS, METHOD STATEMENTS, WORKS /
HEALTH & SAFETY PROCEDURES,INSTALLATION & COMMISSIONING PROCEDURE
• Never ever take any “SHORT CUTS” on any work you do.
can’t follow working procedures.

Course Outline
• ANSI Standard Device Designation and Explanations.
• Basic Electrical Knowledge and Safety Update.
• Test Equipment.
• Electrical Motors
• Cable Glanding / Splicing Procedures.
• IP Rating of Enclosures and Light Fixtures.
• Basic Understanding and Configure of Siemens SIMOCODE-DP System Motor Protection and Control.
• Basic Understanding of SAG Mill Sprint Electric PL/PLX Digital DC Drive

ANSI Standard Device Designation and Explanations.
Master Element is the initiating device, such as a control switch, voltage relay, float switch, etc., which serves either directly or
through such permissive devices as protective and time -delay relays to place an equipment in or out of operation.
Time Delay Starting or Closing Relay is a device that functions to give a desired amount of time delay before or after any point of
operation in switching sequence or protective relay system, except as specifically provided by service function.
Checking or Interlocking Relay is a relay that operates in response to the position of a number of other devices (or to a number of
predetermined conditions) in an equipment, to allow an operating sequence to proceed, or to stop, or to provide a check of the
position of these devices or of these conditions for any purpose.
Master Contactor is a device generally controlled by device function or the equivalent and the required permissive and protective
devices that serves to make and break the necessary control circuits to place an equipment into operation under the desired
conditions and to take it out of operation under other or abnormal conditions.
Stopping Device is a control device used primarily to shut down an equipment and hold it out of operation. (This device may be
manually or electrically actuated, but excludes the function of electrical lockout on abnormal conditions.)
Starting Circuit Breaker is a device whose principal function is to connect a machine to its source of starting voltage.
Anode Circuit Breaker is a device used in the anode circuits of a power rectifier for the primary purpose of interrupting the rectifier
circuit if an arc-back should occur.

Control Power Disconnecting Device is a disconnecting device, such as a knife switch, circuit breaker, or pull-out fuse
block, used for the purpose of respectively connecting and disconnecting the source of control power to and from the
control bus or equipment. Note: control power is considered to include auxiliary power which supplies such apparatus
as small motors and heaters.
Reversing Device is a device that is used for the purpose of reversing a machine field or for performing any other
reversing functions.
Unit Sequence Switch is a switch that is used to change the sequence in which units may be placed in and out of
service in multiple-unit equipment.
Over-Speed Device is usually a direct-connected speed switch which functions on machine over-speed.
Synchronous-Speed Device is a device such as a centrifugal switch, a slip-frequency relay, a voltage relay and
undercurrent relay or any type of device that operates at approximately the synchronous speed of a machine.
Under-Speed Device is a device that functions when the speed of a machine fall below a pre –determined value.
Speed or Frequency Matching Device is a device that functions to match and hold the speed or frequency of a machine
or of a system equal to, or approximately equal to, that of another machine, source, or system.

Shunting or Discharge Switch is a switch that serves to open or to close a shunting circuit around any piece of
apparatus (except a resistor, such as a machine field, a machine armature, a capacitor, or a reactor). Note: This excludes
devices that perform such shunting operations as may be necessary in the process of starting a machine by devices or
their equivalent, and also excludes device function that serves for the switching of resistors.
Accelerating or Decelerating Device is a device that is used to close or to cause the closing of circuits which are used to
increase or decrease the speed of a machine.
Starting-to-Running Transition Contactor is a device that operates to initiate or cause the automatic transfer of a
machine from the starting to the running power connection.
Valve is one used in a vacuum, air, gas, oil, or similar line, when it is electrically operated or has electrical accessories
such as auxiliary switches.
Distance Relay is a relay that functions when the circuit admittance, impedance, or reactance increases or decreases
beyond predetermined limits.
Equalizer Circuit Breaker is a breaker that serves to control or to make and break the equalizer or the current-balancing
connections for a machine field, or for regulating equipment in a multiple -unit installation.
Undervoltage Relay is a relay that functions on a given value of under-voltage.

Temperature Control Device is a device that function to raise or lower the temperature of a machine or other
apparatus, or of any medium, when its temperature falls below, or rises above, a predetermined value. Note: An
example is a thermostat that switches on a space heater in a switchgear assembly when the temperature falls to a
desired value as distinguished from a device that is used to provide automatic temperature regulation between close
limits and would be designated as device function.
Synchronizing or Synchronism-Check Device is a device that operates when two a-c circuits are within the desired limits
of frequency, phase angle, or voltage, to permit or to cause the paralleling of these two circuits.
Apparatus Thermal Device is a device that functions when the temperature of the shunt field or the amortisseur
winding of a machine, or that of a load limiting or load shifting resistor or of a liquid or other medium, exceeds a
predetermined value: or if the temperature of the protected apparatus, such as a power rectifier, or of any medium
decrease below a predetermined value.
Flame Detector is a device that monitors the presence of the pilot or main flame of such apparatus.
Isolating Contactor is a device that is used expressly for disconnecting one circuit from another for the purposes of
emergency operation, maintenance, or test.
Annunciator Relay is a non-automatically reset device that gives a number of separate visual indications of the
functions of protective devices, and which may also be arranged to perform a lockout function.

Separate Excitation Device is a device that connects a circuit, such as the shunt field of a synchronous converter, to a
source of separate excitation during the starting sequence; or one that energizes the excitation and ignition circuits of a
power rectifier.
Directional Power Relay is a device that functions on a desired value of power flow in a given direction or upon reverse
power resulting from arc back in the anode or cathode circuits of a power rectifier.
Position Switch is a switch that makes or breaks contact when the main device or piece of apparatus which has no device
function number reaches a given position.
Master Sequence Device is a device such as a motor-operated multi-contact switch, or the equivalent, or programming
device, such as a computer, that establishes or determines the operating sequence of the major devices in an equipment
during starting and stopping or during other sequential switch operations.
Brush-Operating or Slipping Short-Circuiting Device is a device for raising, lowering, or shifting the brushes of a machine,
or for short-circuiting its slip rings, or for engaging or disengaging the contacts of a mechanical rectifier.
Polarity or Polarizing Voltage Device is a device that operates, or permits the operation of, another device on a
predetermined polarity only, or verifies the presence of a polarizing voltage in an equipment.
Undercurrent or Underpowered Relay is a relay that function when the current or power flow decreases below a
predetermined value.

Bearing Protective Device is a device that functions on excessive bearing temperature, or on another abnormal
mechanical conditions associated with the bearing, such as undue wear, which may eventually result in excessive bearing
temperature.
Mechanical Condition Monitor is a device that functions upon the occurrence of an abnormal mechanical condition
(except that associated with bearing as covered under device function 38), such as excessive vibration, eccentricity,
expansion shock, tilting, or seal failure.
Field Relay is a relay that functions on a given or abnormally low value or failure of a machine field current, or on
excessive value of the reactive component of armature current in an A-C machine indicating abnormally low field
excitation.
Field Circuit Breaker is a device that functions to apply or remove the field excitation of a machine.
Running Circuit Breaker is a device whose principal function is to connect a machine to its source of running or
operation voltage. This function may also be used for a device, such as a contractor, that is used in series with a circuit
breaker or other field protecting means, primarily for frequent opening and closing of the breaker.
Manual Transfer or Selector Device is a manually operated device that transfers the control circuits in order to modify
the plan of operation of the switching equipment or of some of the devices.

Unit Sequence Starting Relay is a relay that function to start the next available unit in a multiple-unit equipment upon the
failure or non-availability of the normally preceding unit.
Atmospheric Condition Monitor is a device that functions upon the occurrence of an abnormal atmospheric condition,
such as damaging fumes, explosive mixtures, smoke or fire.
Reverse Phase or Phase Balance Current Relay is a relay that functions when the polyphase currents are of reverse-phase
sequence, or when the polyphase currents are unbalanced or contain negative phase-sequence components above a given
amount.
Phase-Sequence Voltage Relay is a relay that function upon a predetermined value of polyphase voltage in the desired
phase sequence.
Incomplete Sequence Relay is a relay that generally returns the equipment to the normal, or off, position and locks it out if
the normal starting, operating, or stopping sequence is not properly completed within a predetermined time. If the device
is used for alarm purposes only, it should preferably be designated as 48A (alarm).
Machine or Transformer Thermal Relay is a relay that functions when the temperature of a machine armature or other
load-carrying winding or element of a machine or the temperature of a power rectifier or power transformer (including a
power rectifier transformer) exceeds a predetermined value.
Instantaneous Overcurrent or Rate of Rise Relay is a relay that functions instantaneously on an excessive value of current
or on an excessive rate of current rise, thus indicating a fault in the apparatus or circuit being protected.

AC Time Overcurrent Relay is a relay with either a definite or inverse time characteristic that functions when the current in
an AC circuit exceed a predetermined value.
AC Circuit Breaker is a device that is used to close and interrupt an AC power circuit under normal conditions or to interrupt
this circuit under fault of emergency conditions.
Exciter or DC Generator Relay is a relay that forces the DC machine field excitation to build up during starting or which
functions when the machine voltage has been built up to a given value.
High-Speed DC Circuit Breaker is a circuit breaker which starts to reduce the current in the main circuit in 0.01 second or
less, after the occurrence of the DC overcurrent or the excessive rate of current rise.
Power Factor Relay is a relay that operates when the power factor in an AC circuit rises above or falls below a
predetermined value.
Field Application Relay is a relay that automatically controls the application of the field excitation to an AC motor at some
predetermined point in the slip cycle.
Short-Circuiting or Grounding Device is a primary circuit switching device that functions to short-circuit or to ground a
circuit in response to automatic or manual means.

Rectification Failure Relay is a device that functions if one or more anodes of a power rectifier fail to fire, or to detect and
arc-back or on failure of a diode to conduct or lock properly.
Overvoltage Relay is a relay that functions on a given value of over-voltage.
Voltage or Current Balance Relay is a relay that operates on a given difference in voltage, or current input or output, or
two circuits.
Time-Delay Stopping or Opening Relay is a time-delay relay that serves in conjunction with the device that initiates the
shutdown, stopping, or opening operation in an automatic sequence or protective relay system.
Liquid or Gas Pressure or Vacuum Relay is a relay that operates on given values of liquid or gas pressure or on given rates
of change of these values.
Ground Protective Relay is a relay that functions on failure of the insulation of a machine, transformer, or of other
apparatus to ground, or on flashover of a DC machine to ground. Note: This function is assigned only to a relay that detects
the flow of current from the frame of a machine or enclosing case or structure of piece of apparatus to ground, or detects
a ground on a normally ungrounded winding or circuit. It is not applied to a device connected in the secondary circuit of
current transformer, in the secondary neutral of current transformers, connected in the power circuit of a normally
grounded system.

Governor is the assembly of fluid, electrical, or mechanical control equipment used for regulating the flow of water, steam,
or other medium to the prime mover for such purposes a starting, holding speed or load, or stopping.
Notching or Jogging Device is a device that functions to allow only a specified number of operations of a given device or
equipment, or a specified number of successive operations within a given time of each other. It is also a device that
functions to energize a circuit periodically or for fractions of specified time intervals, or that is used to permit intermittent
acceleration or jogging of a machine at low speeds for mechanical positioning.
AC Directional Overcurrent Relay is a relay that functions on a desired value of AC over-current flowing in a predetermined
direction.
Blocking Relay is a relay that initiates a pilot signal for blocking of tripping on external faults in a transmission line or in
other apparatus under predetermined condition, or cooperates with other devices to block tripping or to block re-closing on
an out-of-step condition or on power savings.
Permissive Control Device is generally a two-position, manually-operated switch that, in one position, permits the closing of
a circuit breaker, or the placing of an equipment into operation, an in the other position prevents the circuit breaker or the
equipment from being operated.
Rheostat is a variable resistance device used in an electric circuit, which is electrically operated or has other electrical
accessories, such an auxiliary, position or limit switches.

Liquid or Gas Level Relay is a relay that operates on given values of liquid or gas level or on given rates of change of these
values.
DC Circuit Breaker is a circuit breaker that is used to close and interrupt a DC power circuit under normal conditions or to
interrupt this circuit under fault or emergency conditions.
Load Resistor Contactor is a contactor that is used to shunt or insert a step of load limiting, shifting, or indicating resistance
in a power circuit, or to switch a space heater in circuit, or to switch a light or regenerative load resistor, a power rectifier, or
other machine in and out of circuit.
Alarm Relay is a relay other than an annunciator, as covered under device function 30 that is used to operate or to operate
in connection with, a visual or audible alarm.
Position Changing Mechanism is a mechanism that is used for moving a main device from one position to another in an
equipment: as for example, shifting a removable circuit breaker unit to and from the connected, disconnected, and test
positions.
DC Overcurrent Relay is a relay that function when the current in a DC circuit exceeds a given value.
Pulse Transmitter is used to generate and transmit pulses over a telemetering or pilot-wire circuit to the remote indicating
or receiving device.

Phase-Angle Measuring or Out-Of-Step Protective Relay is a relay that functions at a pre-determined phase angle between
two voltages or between two currents or between a voltage and current.
AC Reclosing Relay is a relay that controls the automatic reclosing and locking out of an AC circuit interrupter.
Liquid or Gas Flow Relay is a relay that operates on given values of liquid or gas flow or on given rates of change of these
values.
Frequency Relay is a relay that functions on a predetermined value of frequency (either under or over or on normal system
frequency) or rate of change of frequency.
DC Reclosing Relay is a relay that controls the automatic closing and re-closing of a DC circuit interrupter, generally in
response to load circuit conditions.
Automatic Selective Control or Transfer Relay is a relay that operates to select automatically between certain sources or
conditions in an equipment, or performs a transfer operation automatically.
Carrier or Pilot Wire Receiver Relay is a relay that is operated or restrained by a signal used in connection with carrier-
current or d-c pilot-wire fault directional relaying.
Locking Out Relay is an electrically operated hand, or electrically reset relay or device that functions to shut down or hold an
equipment out of service, or both, upon the occurrence of abnormal conditions.

Differential Protective Relay is a protective relay that functions on a percentage or phase angle or other quantitative
difference of two currents or of some other electrical quantities.
Auxiliary Motor or Motor Generator is one used for operating auxiliary equipment, such as pumps, blowers, exciters,
rotating magnetic amplifiers, etc.
Line Switch is a switch used as a disconnecting, load-interrupter, or isolating switch in an AC or DC power circuit, when this
device is electrically operated or has electrical accessories, such as an auxiliary switch, magnetic lock, etc.
Regulating Device is a device that functions to regulate a quantity, or quantities, such as voltage, current power, speed,
frequency, temperature, and load at a certain value or between certain (generally close) limits for machines, tie lines, or
other apparatus.
Voltage Directional Relay is a device which operates when the voltage across an open circuit breaker or contactor exceeds a
given value in a given direction.
Operating Mechanism is the complete electrical mechanism or servomechanism, including the operating motor, solenoids,
position switches, etc., for a tap changer, induction regulator, or any similar piece of apparatus which otherwise has no
device function number.

Voltage and Power Directional Relay is a relay that permits or causes the connection of two circuits when the voltage
difference between them exceed a given value in a predetermined direction and causes these two circuits to be
disconnected from each other when the power flowing between them exceeds a given value in the opposite direction.
Field-Changing Contactor is a contactor that functions to increase or decrease, in one step, the value of field excitation on a
machine.
Tripping or Trip-Free Relay is a relay that function to trip a circuit breaker, contactor or equipment, or to permit immediate
tripping by other devices; or to prevent immediate re -closure of a circuit interrupter if it should open automatically even
though its closing circuit is maintained closed.* Used only for specific applications in individual installations where none of
the assigned numbered functions.
SCADA Supervisory Control and Data Acquisition(On site we call it “WinCC”)
Serial Link cable between devices which carries electrical pulses in series
Multi-drop is a shared serial link between several devices using some form of addressing scheme.
Protocol the language used by devices to communicate with each other.
Master/Slave is a protocol which uses a one Master to many Slaves relationship between devices.

Timeout is a period of time allowed for a device to respond.
Retry is a re-transmission of a message which did not receive a valid response.
Error Detection used to ensure a message is received without error.
Baud Rate is also called Bits per Second – speed of transmission.
Data Bits is the number of bits per packet that make up the data.
Stop Bits is the number of bits per packet that make up the stop sequence.
Thermal Capacity of the motor is the heat input required to take the motor to the maximum temperature it can withstand
without suffering damage. The thermal capacity is derived from the maximum time the motor can be stalled / locked. The
engineer uses the maximum stall time when cold to select a protection curve number to ensure a trip will occur prior to the
maximum stall time.
Hot / Cold Ratio Defined as the ratio of stalled time of the motor when hot against stalled time when cold. For example, Stall
time (Hot) = 6s and Stall Time (Cold) = 9s then Ratio = 6/9 x 100 = 66%
Cooling Time is the stopped motor cooling time defines the length of time for a motor to reach a steady ambient
temperature from its maximum temperature (I.e. 100% thermal capacity).

Basic Electrical Knowledge and Safety Update.
Basic Electricity Knowledge Update:
What is electricity? Electricity is the movement (flow) through a conductor of electric charges. In solids such as metal
wire, the charges consist of negatively charged electrons. In gases and liquids, we have both electron and ion flow. As
shown above a typical atom consists of a nucleus composed of positively charged protons and neutral (no charge)
neutrons. Much like a solar system, atoms have rings of negatively charged electrons that orbit the positively charged
nucleus. In a normal atom the number of positive and negative charges are equal, leaving the entire atom with no
electric charge. The number of protons is also known as atomic number and determines what the chemical element is.
Helium has two protons; copper has 29 protons, while aluminum has 13 protons
The Law of Charges states that unlike charges attract while like charges repel. In the helium atom above, the attraction of
two positively charged protons in the nucleus keep the two electrons from flying off into space. Centrifugal force from
the electrons spinning around the nucleus keeps the electrons from falling inward. If we were to add enough energy
(heat, light, friction, etc.) to the atom, the electrons will spin faster and faster until one of them is thrown off and
becomes a free electron.

This would leave the atom with a net positive charge as we have two positive protons and one negative electron. This is
called an iron and an ion can be negative or positive. Note that ions and other charged particles can be influenced by a
magnetic field.
Conductors
As illustrated above many chemical elements have rings (shells) of electrons that vary from two to thirty two. In the
electrical industry we are concerned only with the very outer ring known as the valence ring. The valence shell contains
between one and eight electrons. The number of electrons in the valence ring determines if the atom is a conductor or
an insulator. The octet rule in chemistry says for an atom to be stable, it must have eight electrons. In the case of
sodium above, we could add seven electrons or remove one electron. It’s much easier to remove the one electron. In
general a conductor is an atom with one to three valence electrons. Copper, silver, and gold all have one valence
electron. Iron, cobalt, nickel, and zinc have two, aluminum has three. Gold, silver, and copper are the best conductors.
In electric wire we use mainly copper and aluminum. All are metals and besides being good electrical conductors, are
also good heat conductors. An alloy consists of mixture of two or more metals. Common alloys include brass, bronze,
pewter, and stainless steel. Alloys have properties superior to the metals that went into them. Brass (mixture of copper
and zinc) is harder and more durable than either copper or zinc. Stainless steel (iron mixed with carbon, chrome and
nickel) resists rust and is stronger than iron alone. Tin mixed with lead makes electrical solder. The electrical
conductivity of an alloy falls between the metals that went into them. Brass is a better conductor than zinc, but not as
good as copper. In copper wire we use pure copper to make the best conductor. The sodium above is a metal and would
be a good conductor, but can’t be used because it burns in the presence of air or water. Silver is a better conductor than
copper, but the cost is too high to use for wire. A common alloy in the electrical industry is chrome, an alloy of
chromium and nickel. It’s used to make heating elements.

Insulators
Chemical elements with five to eight valence electrons are insulators. Many of these elements are gases (oxygen, nitrogen,
argon, helium, etc.) or unstable solids such a sulfur or phosphorus. In the real world insulators are often molecules and
compounds. (Mixtures of atoms.) Common insulators include glass, rubber, mica, plastics, wood, etc. They are insulators
because their chemical structures tightly bound the electrons. Think of it as electron super-glue. If enough force is
supplied, electrons can be stripped away, but often cling to the surface. Typical is walking across a carpet and getting a
minor shock when one touches a metal doorknob causing an electric discharge. We call this static electricity. Lightning is
also static electricity.
Semiconductors
A third class of materials is called semiconductors. They are neither good insulators nor good conductors, but somewhere
in between. They have four valence electrons and include Carbon, silicon, and germanium. Silicon and germanium are
used to make semiconductor devices such as diodes and transistors while carbon is not. Carbon in its diamond form is an
insulator and in its graphite form is a conductor used to make motor brushes.

Electron Flow
Electricity is the flow of electric charges. In this discussion we will stick to solids. This is accomplished by using some form of
energy to knock a valence electron off one atom into the next atom to the next, etc. Think of this as a water pipe full of
Ping-Pong balls where a ball is inserted into one end and a ball falls out the other end. Energy is transferred from one ball to
the next ball down the line. Metals have loose valence electrons and require little energy to dislodge them. The electrons
are so tightly bonded in insulators massive amounts of energy are needed to dislodge an electron. The process often
destroys the insulator. Electron flow goes from negative (-) to positive. (+) In this class we will use conventional flow.
Although it has been established that the electron theory is probably correct, the conventional current theory is still used to
a large extent. There are several reasons for this. Most electronic circuits use a negative ground or common. When this is
done, the positive terminal is considered to be above ground, or hot. It is easier for most people to think of something
flowing down rather than up, or from a point above ground to ground. An automobile electrical system (negative ground) is
a good example of this type of circuit. Most people consider the positive battery terminal to be the “hot” terminal.
Various symbols for grounds.
Do not assume they are connected to each other or are always the same! Many of the people that work in the electronics
field prefer the conventional current flow theory because all the arrows on the semiconductor symbols point in the
direction of conventional current flow. If the electron flow theory is used, it must be assumed those current flows against
the arrow. In the military and here I'll use electron flow.

Electrical measurements generally use engineering (and
scientific) notation. Engineering notation differs from
the standard metric in that it uses steps of 1,000
instead of steps of
For example if we have a 10 kilo-ohm (10k) resistor and
want to convert to ohms, we multiply by 1000 to get
ohms, in this case 10,000 ohms. If we have a 27,000-
ohm resistor and want to convert to kilo-ohms, we
divide by 1000 to get 27 kilo-ohms or 27k. Another
example is if we have .5 volts, we would change to milli
volts (mV) by multiplying by 1000 to 500 milli volts (mV)
or often expressed as 500mV. If we want to change milli
volts to volts we divide by 1000. Note that milli amps
(mA) is used in electronics more than electricity.
Ohms Law
Ohm's Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. One amp flowing through
one ohm produces one volt. (I) Current is what flows on a wire or conductor like water through a pipe. Current (electrons)
flow from negative to positive through a conductor. Current is measured in (A) amperes or amps.

A coulomb is a quantity measurement of electrons. One coulomb equals 6,250,000,000,000,000,000 electrons. The definition
of one amp (A) is one coulomb per second passing a point. The letter I, stands for intensity of current flow, or A, which stands
for amps, are often used in Ohm's Law formulas. (E) Voltage is the difference in electrical potential between two points in a
circuit.
It's the push or pressure behind current flow through a circuit, and is measured in (V) volts.
Voltage is the potential energy of an electrical supply stored in the form of an electrical charge, and the greater the voltage
the greater is its ability to produce an electrical current flowing through a conductor.
This energy has the ability to do work. Voltage is sometimes called Electromotive
Force, (EMF) with the circuit symbol V, although E is mostly used today. Here I'll use E. (R) Resistance (electrical friction)
determines how much current will flow through a component. Resistors are used to control voltage and current levels.
Resistance is measured in Ohms, using the Greek symbol Omega. (Looks like an upside-down horseshoe.)
An ohm is a measurement of resistance (R) in an electric circuit. The letter R is used to represent Ohm's Law formula.
The watt (W) is a measurement of power in an electrical circuit. The letter P represents power in Ohm's Law formula while
Watts is the unit of measurement. (P) Power is the amount of current times the voltage. These are the main formulas to
know:
Also: P = I * V

Resistors
Resistors are used in two main applications: as voltage dividers and to limit the flow of current in a circuit. The value of a
fixed resistor cannot be changed. There are several types of fixed resistors, such as composition carbon, metal film, and wire
wound. Carbon resistors (not much used today) change their value with age or if overheated. Metal film resistors never
change their value, but they are more costly than carbon resistors.
Fixed resistors
The advantage of wire wound resistors is their high power ratings. Resistors often
have bands of color to indicate their resistance value and tolerance. Resistors are
produced in standard values.

Thermistors
A thermistor is a resistor that changes value with temperature. The resistance decreases with increased temperature, we
say the thermistor has negative temperature coefficient. If the resistance increases with an increase in temperature, we
say the thermistor has a positive coefficient. Thermistors can be used to measure temperature.
Photocells (also called photo resistors) decrease resistance in the
presence of light based on light intensity. They are used to measure
light intensity or as an “electric eye” in streetlights.
Variable resistors (or potentiometers) can change their value
by turning a knob, etc. These are the older style “volume
controls” used in consumer electronics.

The internal construction of a potentiometer has a slider attached to the shaft
which when adjusted changes resistance in relation to the two outer
terminals.
In the above circuit diagram a potentiometer is
connected to a 12 volt DC source. As the control is
adjusted the voltmeter will read 0-12 volts. Note the
grounds donate a common connection.

Proper Use of a Multimeter
In measuring current with a multimeter the student has to
understand how to attach the meter. When measuring
current the ampmeter must be placed in series by breaking
the electrical path and inserting the ammeter into the path.
Note that an ammeter should never be placed across
(parallel) to any component or the meter will be damaged or
blow a fuse. An ammeter has a very low internal resistance.
More on that later. This differs from a clamp-on ammeter that
measures the magnetic field generated by electrical current
flow. We will look more into that in the section on magnetics.
To measure voltage the meter must be placed in parallel as
shown above. Voltmeters have a high internal resistance.
Meters - Measuring Current
Ammeter must be part of the circuit to
measure the current
VOM – multimeter that measures E, I, R

Meters - Measuring Voltage
Voltmeter measures across the circuit (in parallel to the
voltage to be measured)
Meters - Measuring Resistance
Ohmmeter: measures across the resistor (but be sure the circuit is not turned on “hot”).
Puts in a known voltage and measures the current, so it requires a battery. If the circuit is energized, will give the
wrong reading! Never leave a multimeter set at “ohms” – will run down its battery!

Ohms Law
Pictured above is the Ohms Law pie chart that has twelve formulas broken into four
quadrants.
We have a power source and a load R1. Current will flow from negative to positive as
shown by the arrows and the resistance of R1 will limit the current.
Let’s look at several sample problems and how to solve them. For this class we will find
all values including I in amps, V in volts, R in ohms, and P in watts. Note that with
resistive loads AC and DC work the same.
Note there are no multiply or divide keys on a computer keyboard, so we use / for divide and * for multiply.
Problem 1:
An electric heating element has a resistance of 16 ohms and is connected to 240 volts AC. What is the current and how
much heat is produced?
How to proceed: First we ask, “What do I know?”
We know the resistance R = 16 ohms. We know voltage V = 240. And we know our two formulas stated earlier as I = V/R
and I*V = P.
First we find I: I = V/R = 240/16 = 15 amps. Now we find P (the heat produced in this case): P = I*V = 15*240 = 3600 watts.

Problem 2:
A 480-volt circuit has a current flow of 3 amps. What is the resistance R and the power P?
What do I know?
V = 480 volts; I = 3 amps.
P = I*V = 480*3 = 1440 watts.
To find R we must transpose the two formulas: I = V/R or 3 = 480/R;
Divide both sides of the equation by 480 (or multiply by 1/480) we get 3/480 = 1/R (the 480 cancel):
This comes out to be .00625 = 1/R; now we take the reciprocal of both sides of the equation: the reciprocal of 1/R = R;
reciprocal of .00625 = 1/. 00625 = 160ohms. (One can also use the reciprocal key on their calculator too.) Thus R = 160 ohms.
For the student terrified of mathematics, we can use a pie chart. In our previous problem we knew V = 480 volts, I = 3 amps,
and P = 1440 watts. Now we need to find R, we look at the formulas in the lower right-hand quadrant. Any of the three will
work, but V/I is the easiest to use.
R = V/I = 480/3 = 160. We get the same answer. Whether one wants to use math or the pie chart is an individual choice. Often
we use both.
Problem 3:
An electric motor has an apparent resistance (more on apparent resistance in AC) of 15 ohms. With eight amps of current,
what is the voltage and power?
What do we know? R = 15 ohms; I = 8 amps.
Using the pie chart to find P (lower left quadrant) knowing both R and I we use I squared times R;
P = (8*8) * 15 (do the 8 times 8 first); 64*15 = 960 watts.
To find V (upper right quadrant) we can use I*R = 8*15 = 120 volts.

Series Circuits
Pictured is a typical series circuit such as Christmas tree lights. When we close the
switch, the lamps will light up as current flows through the lamp filaments
generating intense heat, which produces light.
Properties of series circuits:
The current through each device in a series circuit is equal. In this case each light bulb has the same identical current
through each individual filament. In we will assume each light bulb is 40 watts at 15 volts. Using I =P/V = 40/15 = 2.67 amps.
The power source must supply 2.67 amps to power the circuit.
Failure of any one element in the string will break the current path for all devices in the string. If one light bulb burns out
(opens), all of the lights would turn off regardless of the power switch. This is what happens to Christmas lights when a
single bulb goes bad. Note that all of the voltage supplied to a series circuit will appear across the open element.
The sum of the voltage drops across each element in a series circuit equals the voltage supplied by the source. Let’s
assume each of the eight light bulbs is rated at 15 volts. 15 volts times eight equals 120 volts. That is the voltage that must
be supplied from the source to light up all eight light bulbs.
The power consumed by each element in a series circuit equals the total power supplied by the source. In this case let’s
assume each light bulb uses 40 watts of power. 40 times eight equals 320 watts of power that must be supplied by the
source.

The total resistance of a series circuit is the sum of the individual resistances. In the above example we have been using a
string of 40-watt bulbs at 15 volts each. We use the formula V times V divided by P from the pie chart to get R = 5.625 ohms
for each lamp. The total resistance of the circuit is 5.625 * 8 = 45 ohms. There is another way to check this to see if we are
right. I = 2.67 amps and P = 320 watts. 2.67 * 2.67 = 7.13, so 320 divided by 7.13 = 44.88 ohms. This is a typical example of
rounding errors.) So I now know the original answer was correct.
In the previous example we used eight light bulbs in series and all had identical power, resistance, and voltage ratings. All
of the factors are directly related and depend on each other. So we had a nice uniform voltage drop and resistance from
one circuit element to the next. In the figure above we have replaced the light bulbs with five resistors. These could be
resistors, heating elements, lamps, etc. Here I will assume resistors.
We are using a DC source and not an AC source. AC has no polarity but DC does. If one placed a DC meter across resistor 1
(red lead on the positive side, black lead to the battery side) we would read the voltage drop across the resistor. Reverse
the meter leads and we will read a negative voltage, so turn the leads around.

The voltage across resistor 1 (R1) depends on the value of the resistor and the current through it. (Use the formula I*R from
the chart.) For example if the resistance of R1 is 2000 ohms (2k) and the current 25 milliamps (mA), how do we solve the
problem?
First convert milliamps (mA) to amps by dividing by 1000 to get .025 amps.
Next multiply .025 by 2000 ohms (or 2k) to get voltage across R1 which is 50 volts. How much power does the resistor use?
Multiply 50 volts times .025 amps we get 1.25 watts. Resistors come in standard power ratings such as one-eight watt,
quarter watt, 1 watt, 2 watt, etc.
We would have to use at minimum a 2 watt or higher else the resistor will overheat and fail.
What about total power and total resistance? If all five resistors were the same value of 2k, it would be easy to multiply by
five. But here we have different values for each resistor. R2 = 3k; R3 = 1.5k; R4 = 1.2k; R5 = 2.2k. Note the current is identical
through each resistor at .025 amp.
The voltage across R2 = 3000 * .025 = 75 volts and P = 1.875 watts or 1875 mW.
The voltage across R3 = 1500 * .025 = 37.5 volts and P = .9375 watts or 937.5 mW
The voltage across R4 = 1200 * .025 = 30 volts and P = .750 watts or 750 mW.
The voltage across R5 = 2200 * .025 = 55 volts and P = 1.375 watts or 1375 mW.
Total P = 1.25 + 1.875 + .9375 + .750 + 1.375 = 6.1875 watts.
Total V = 50 + 75 + 37.5 + 30 + 55 = 247.5 volts.
Total R = 2k + 3k + 1.5k + 1.2k + 2.2k = 3.4k or 3400 ohms.
Check: total P = total V * total I = 247.5 volts * .025 amps = 6.1875 watts.

One last thing to note is the voltage drop in a series circuit is proportional to resistance. The higher the resistance, the
higher the voltage drops. So the highest value resistor (3k) had the highest voltage drop at 75 volts.
An application
On thepicture two separate series circuits. We have a photocell in series with a 1000-ohm
(1k) fixed resistor. If we connect meter from ground to point “V” what will our meter
read? Remember a photocell decreases resistance in the presence of light. Let’s assume
VCC = +12 volts while ground is negative.
Let’s assume in the dark the photocell resistance = 11,000 ohms (11k). We have a total circuit resistance of 1k + 11K = 12k
(which we will call Rt) which gives us a current of 12 volts divided by 12,000 ohms = .001 amp or 1 mA.
In the left-hand circuit the voltage drop across R1 (or VR1) = 11,000 ohms *. 001 amps = 11 volts. The same current flow
through R2 so VR2 = 1000 ohms *.001 amps = 1 volt. As in all series circuits the voltage drops when added together should
equal the source voltage. 1 volt + 11 volts = 12 volts.

So the voltmeter on the left-hand circuit will read 1 volt while it will read 11 volts on the right-hand circuit. Now we shine
a bright light onto the photocell and its resistance drops to 1000 ohms. What will the meter read now? Our total resistance
(Rt) = 1000 ohms +1000 ohms = 2000 ohms. (2k)
Our current = 12 volts / 2000 ohms = .006 amp or 6 mA. VR1 = 1000 ohms *.006 = 6 volts. VR2 = 1000 ohms * 1000 = 6
volts. Now the voltmeter will read 6 volts on either circuit.
With the left-hand series circuit voltage increased with light intensity while it dropped on the right-hand circuit. By
measuring the voltage across either circuit we can measure light intensity. This is exactly what light meters did on older
cameras. We could have easily replaced the photocell with a thermistor (to measure temperature or any kind variable
resistance sensor and got the same effect.
Parallel Circuits

Pictured above is a typical parallel circuit with the light bulbs connected in parallel and all three in series with a fuse. Fuses
and circuit breakers as current operated devices are always connected in series. See page 340 in the textbook.
Parallel circuits differ from series circuits in several important ways:
The voltage across each element is a parallel circuit is identical. If the voltage from the generator is 120 volts, then the
voltage measured across each light bulb would be 120 volts.
The current through each element of a parallel circuit is different. In this case we could have a 120-watt, a 240-watt, and a
60-watt light bulb all connected to the same power source without one effecting the other.
The failure of one element in a parallel circuit will not affect the other elements. For example in household electric wiring
a blown (open) light bulb in the kitchen won’t affect the living room.
The total current drawn from the generator equals the sum of the currents from each circuit element. From the examples
above with three bulbs each at 120 volts, the 120 watt bulb draws 1 amp, the 240 watt bulb draws 2 amps, and the 60 bulb
draws .5 amp, the total I = 1 + 2 + .5 = 3.5 amps. (Use P/V)
The total power drawn from the generator is the sum of the power drawn by each element. In the above example total P =
120 watts +240 watts + 60 watts = 420 watts. Check: divide 420 watts by 3.5 amps =120 volts.

The total resistance of a parallel circuit is always less than the least resistance. Using the examples above, the resistance of
the 120 watt bulb = V divided by I = 120 volts divided by 1 amp = 120 ohms. The resistance of the 240 watt bulb = 120 volts
divided by 2 amps = 60 ohms. The resistance of the third bulb = 120 volts divided by .5 amps = 240 ohms. To see if the above
statement is correct, let’s divide the 120 volts by the total current (I) of 3.5 amps = 34.3 ohms. Note that the lower the
resistance of an element in a parallel circuit the higher the wattage or power drawn from the generator, thus the 240 watt
bulb has the least resistance. One final question: what size fuse should we use? Fuses also come in a number of sizes, so at
3.5 amps total we would have to use a fuse rating greater than 3.5 amps. 4 or 5 amps would be fine. 30 amps would be
absurd because the idea is to blow the fuse before the wiring catches fire. Never replace a fuse with a value higher than the
original!
The example is a simplified view of home electrical wiring. (120 volts) The wall
outlets are wired in parallel. If one was to plug a 1200-watt hair dryer into one
wall socket and a 1500-watt microwave into a neighboring wall socket, could a
20-amp breaker carry the load? The answer is no. 1200 watts at 120 volts = 10
amps. 1500 watts at 120 volts = 12.5 amps. Total = 22.5 amps. Also note the
light bulbs are wired in series with a switch, but both are wired in parallel
with the wall sockets and all are wired parallel with the panel box. This is
called a combination circuit. Most electrical/electronic devices use
combination circuits

As the circuit illustrates when resistors are wired in series, the total
resistance is obtained by adding the resistor values

Test the Theory
In the case of parallel circuits if the resistors have the same value take the value
of one resistor and divide by the number of resistors. Take two 1000-ohm
resistors and wire them in parallel. Measure the resistance. Did the measured
value match the expected value?
Test the Theory
For resistors that are not the same we use the reciprocal formula. (Page 138 in the textbook.) If R1 = 1000 ohms, R2 = 2000
ohms, and R3 = 3000 ohms, calculate the total resistance. With the battery voltage at 12 volts, calculate on paper the
current though each resistor and the total current in amps and milliamps. Then measure the current through each resistor
to see if they match the current supplied by the battery. How do we attach an ammeter to check current?
Test the Theory
Wire a 100-watt light bulb in series with a 40-watt light bulb. Apply power, which bulb is brighter? Why? Measure the
voltage drop across each individual light bulb. Do the measured values when added equal the voltage supplied?

Resistor Information
Resistor symbols differ
in different countries
More resistors symbols
How to read a color code on a resistor. For example a 3.3k (3300) ohm resistor
color code would be orange-orange-red or 33 * 100. What is the color-codes for
a 1k, a 2k, and a 3k resistor?

Measuring Resistance, In Circuit and Out
The resistor is the fundamental electronic component. By resisting the flow of electrons in a simple and predictable way, a
resistor allows the designer to easily manipulate currents and voltages—and currents and voltages are what circuits are all
about.
Before You Measure
The resistance, or simply the “value” of a resistor determines how it will influence the circuit to which it is connected. You
need to know the resistance of your resistor—sometimes the approximate value is fine--but sometimes you need precision.
The value of a resistor is usually indicated on the component itself, with either old-fashioned colored bands or printed
numerals. But these are nominal values, meaning that the actual resistance can be a certain percentage higher or lower than
this indicated value. If the tolerance of the resistor is 10%, for example, a “1000 ohm” resistor could actually be anywhere
between 900 and 1100 ohms.
Why Measure?
So if the resistance value is labeled right there on the resistor, why would you need to measure? There are two reasons:
• You may not be able to confidently determine the resistance from the label—maybe the component is old and the label is
faded, or maybe you don’t understand the color code.
• You may need to know the exact value of a specific resistor, not the nominal value. A high-precision circuit requires high-
precision components. If the reference voltage for an analog-to-digital converter is determined by an external resistor, you
need to know the exact value of that resistor in order to accurately interpret your digitized measurements

The Easy Way
The most common and simplest way to measure resistance is with a digital multimeter, or DMM. This indispensable device
knows all about Ohm’s law and is happy to do the work for you: when you connect the terminals of the resistor to the two
probes, it supplies a known current, measures the resulting voltage drop, and calculates the resistance. The trouble is, this
approach only works if you can take your resistor out of the circuit; the DMM’s reading cannot be trusted if the resistor’s
terminals are connected to other components. So if you need to know the value of a resistor that cannot be isolated from
other components, you will have to be more creative.

Web Site to do Resistor Calculations
for you
https://www.eeweb.com/toolbox/
4-band-resistor-calculator/
https://www.eeweb.com/toolbox/
5-band-resistor-calculator/
https://www.eeweb.com/toolbox/6
-band-resistor-calculator
Or
https://www.elprocus.com/online-
resistor-color-code-calculator/

FORMULAS, EQUATIONS & LAWS
Symbolic:
E =VOLTS ~or~ (V = VOLTS)
P =WATTS ~or~ (W = WATTS)
R = OHMS ~or~ (R = RESISTANCE)
I =AMPERES ~or~ (A = AMPERES)
HP = HORSEPOWER
PF = POWER FACTOR
kW = KILOWATTS
kWh = KILOWATT HOUR
VA = VOLT-AMPERES
kVA = KILOVOLT-AMPERES
C = CAPACITANCE
EFF = EFFICIENCY (expressed as a decimal)
DIRECT CURRENT:
AMPS= WATTS÷VOLTS I = P ÷ E A = W ÷ V
WATTS= VOLTS x AMPS P = E x I W = V x A
VOLTS= WATTS ÷ AMPS E = P ÷ I V = W ÷ A
HORSEPOWER= (V x A x EFF)÷746
EFFICIENCY= (746 x HP)÷(V x A)

AC SINGLE PHASE ~ 1ø
AMPS= WATTS÷(VOLTS x PF) I=P÷(E x PF) A=W÷(V x PF)
WATTS= VOLTS x AMPS x PF P=E x I x PF W=V x A x PF
VOLTS= WATTS÷AMPS E=P÷I V=W÷A
VOLT-AMPS= VOLTS x AMPS VA=E x I VA=V x A
HORSEPOWER= (V x A x EFF x PF)÷746
POWERFACTOR= INPUT WATTS÷(V x A)
EFFICIENCY= (746 x HP)÷(V x A x PF)
AC THREE PHASE ~ 3ø
AMPS= WATTS÷(1.732 x VOLTS x PF) I = P÷(1.732 x E x PF)
WATTS= 1.732 x VOLTS x AMPS x PF P = 1.732 x E x I x PF
VOLTS= WATTS÷AMPS E=P÷I
VOLT-AMPS= 1.732 x VOLTS x AMPS VA=1.732 x E x I
HORSEPOWER= (1.732 x V x A x EFF x PF)÷746
POWERFACTOR= INPUT WATTS÷(1.732 x V x A)
EFFICIENCY= (746 x HP)÷(1.732 x V x A x PF)

Basic Electricity Safety Update:
Qualified Employees:
Have training to avoid the hazards of working on or near an exposed electrical parts
Are trained to work on energized electrical equipment
Can lock out or tag out machines and equipment
Know the safety‐related work practices of the OSHA regulations and the NFPA standards, including
required PPE
Qualified employees have the training to know how to recognize and avoid any dangers that might be present when working on
or near exposed electrical parts.
Qualified employees know how to lock out and tag out machines so the machines will not accidentally be turned on and hurt
the employees that are working on them.
Qualified employees also know safety‐related work practices, including those by OSHA and NFPA, as well as knowing what
personal protective equipment should be worn.
Affected Employees:
Can work on a machine or piece of equipment
Cannot work on electrical devices
DO NOT have the training to work on energized parts
If you are not qualified to work on electrical equipment, but are still required to work near electrical equipment, you are
considered to be an affected employee.
Safe working practices for affected employees are just as important as practices for qualified employees.

As an affected employee, you will be working on machines and other pieces of equipment, but not on electrical devices. You
will, though, still be working around electrical parts that can kill you.
Since you do not have the training to work on these parts, you are considered to be an affected
employee because just being near some of these parts can be very dangerous.
What Is Electricity?
Electricity is a type of energy
Electricity is everywhere: motors, heaters, lights, speakers
To help you understand what an arc flash is, we will start by introducing electricity.
Electricity is a type of energy. In your home you can see electricity being used everywhere.
Electricity can make the motors of a washing machine, refrigerator, or blender spin.
Electricity can heat up rooms with a heater, dry your clothes in a dryer, and toast bread in a toaster.
Electricity can also be used to light up rooms, create sounds in speakers, and run a computer.
How Is Electricity Used In Manufacturing?
Lights in the building, Motors, Welders, Control devices
In a manufacturing setting, electricity is used even more. Electricity provides power to practically
every piece of equipment in a manufacturing facility.
It is used to light the buildings, provides power to electric motors, gives the power needed to run
a welder, and also provides the control power needed so an operator can run a piece of
machinery from a distance.

Electricity
Electricity is the flow of energy from one place to another
A flow of electrons (current) travels through a conductor
Electricity travels in a closed circuit
When you think of electricity you should think of it as a form
of energy that flows from one place to another.
Electricity involves the flow of electrons in a closed circuit through a conductor. But don’t worry if you don’t understand all of
this yet. We will cover each of these items and more in detail as we progress through the training.
Electric Charge, Static Electricity, and Current Electricity
When an electric charge builds up in one place it is called static electricity
Electricity that moves from one place to another is called current electricity
The electrons that are involved in electricity have an electric charge.
When an electric charge builds up in one place it is called static electricity.
We can understand electric charge by looking at someone touching a static electricity generator.
In the picture her hair is standing up because of an electric charge that builds up in her hair.
The electricity that builds up when you scoot your feet on the floor on a cool, dry day and shock someone is also because of
static electricity.
Lightning is another spectacular display of static electricity.
Electricity that moves from one place to another is called current electricity.
An electric current, then, is the flow of electric charge. Electric currents move through wires to make motors spin, lights light
up, and heaters warm a house.

Conductors
Conductors allow the flow of electricity
Silver, Copper, Gold, Aluminum, Iron, Steel, Brass, Bronze, Mercury, Graphite, Dirty water and Concrete
Electric current flows through electrical conductors.
A conductor is anything that allows the flow of an electric charge. A common conductor you probably already know about is
copper. Copper wires conduct electricity.
Copper, as well as aluminum, is often used to deliver electric current to machines in manufacturing settings as well as any
electric appliances at home.
As you can see from the slide, most metals are good conductors. Some of the conductors listed that might surprise you are
dirty water and concrete.
Insulators
Insulators do not normally allow the flow of electricity
Glass, Rubber, Oil, Asphalt, Fiberglass, Porcelain, Ceramic, Quartz, (dry) cotton, (dry) paper, (dry) wood, Plastic, Air, Diamond
and Pure water.
An insulator is just the opposite of a conductor. It does not allow the flow of an electric charge and keeps electricity from
getting to unwanted areas.
The plastic insulation around a copper wire is an example of an insulator. Others you might not have thought of are glass, oil,
and pure water.
As we go further into the training we will find out that electricity can flow through insulators under certain circumstances.
An arc flash is one of the circumstances where air actually acts as a conductor.

Three Basic Hazards
Shock/Electrocution, Arc Flash and Arc Blast
Now that you have a fairly good idea of what electricity is, let’s go over some of the hazards involved in working around
electrical devices.
They include shock, electrocution, arc flash, and arc blast.
These hazards are present in any circuits over 50 volts.
Dangers of Shock and Electrocution
Electricity can kill you
Most deaths are preventable
While electricity is useful, it can also hurt or kill you. Accidents from electricity happen far more
often than you would like to think.
Electricity has long been recognized as a serious workplace hazard, exposing employees to
electric shock, electrocution, burns, fires, and explosions.
If a person is killed by getting shocked, then they are considered to have been electrocuted.
In 2009, 268 workers died from electrocutions at work, accounting for almost 5 percent of all
on‐the‐job fatalities that year, according to the Bureau of Labor Statistics.
30,000 victims each year are lucky enough to only get shocked and not killed.
What makes these statistics more tragic is that most of these fatalities and injuries could have
been easily avoided by using safe work practices such as making sure that electrical equipment
is locked out, tagged out, and de-energized.

Scare Pictures
While no one likes seeing pictures of injuries, we do need to show you just how devastating
electrical injuries can be. These next five pictures are from OHSA’s web site.
Entrance Wound
When you are shocked, electricity travels through your body. Severe injuries
can show up where the electricity enters and leaves your body.
This picture shows how the resistance of the body turns electricity into heat.
This man was lucky to survive since the electricity entered his body so close to
his spinal cord.

Exit Wound
Here is a picture of where electricity exited a man’s foot.
The charred hole is just the surface of the wound. As the electricity traveled through his
foot, it created lots of heat and burned the inside of his foot so much that the doctors had to
cut the foot off a few days after the injury.
Internal Injuries
In this picture, the worker was shocked by the metal tool he was using, such as a
pair of pliers. The resistance of the metal made it heat up, causing the burnt skin
below his thumb.
The visible part of the wound looks bad, but there were severe internal injuries that
were not immediately visible. These internal injuries were from the current flowing
through his hand.

This is the same hand a few days later. As you can see there was so much damage that
skin had to be sliced open to make room for all the swelling.
The injury below the burn from the metal tool was caused from heat as well, but the
heat in these areas was from the current going through his hand, not the heat of the
tool.
Involuntary Muscle Contraction
In this picture, a worker fell and grabbed a power line to catch himself.
There was so much current in his hand that his first two fingers were mummified and
had to be removed.
His hand is bent like this because as the tendons in his hand were cooked, they shrunk,
painfully drawing up the workers hand.

Getting Shocked
You become part of the circuit.
The current traveling through your body can kill you.
Most people know what an electrical shock is. The pictures gave you a good idea of what can happen when you are
shocked, but let’s go over some of the details of shock and electrocution some more.
Electric shocks can be harmless like getting shocked when touching a doorknob after walking on carpet, or a shock can be
deadly.
An electric shock occurs when current passes through the body. The current can cause damage to muscles (including heart
muscles), the nervous system, and other parts of the body.
Getting shocked means your body is becoming part of the circuit. You become a conductor because of the current running
through your body.
Causes of Electric Shock
Two different live wires
A live wire and a ground wire
There are many ways that a person’s body can become part of an electrical circuit and get
shocked.
You will get an electric shock if you touch a live wire and an electrical ground or if you touch a live wire and another wire of
a different potential.
So, if you touch any live wire and then touch either a different live wire or a ground wire, you can get shocked.
Many have been shocked at home, but at the work place, voltage and current are much higher creating a greater chance of
getting hurt.

Electrocution
Electrocution means death by electricity.
Less resistance leads to more current passing through the body.
Affected employees must pay special attention to electrical hazards that can cause electrocution because they often work
near electrical circuits.
Electrocution, then, occurs when a person is shocked with enough current that they die. This is because the large amounts of
current flowing through the body can cause severe internal and
external injuries.
The chances of being electrocuted go up when working around water or when you are sweating OR when you are not
wearing the proper protective clothing.
Shock Can Occur Without Touching Live Parts
Circuits can be completed through the air
If you think you have to actually touch live wires to get shocked, you would be wrong. Just as static electricity can shock you
even before you touch a door knob, electric currents can reach out and shock you if your body gets in a position that it could
become part of the circuit.
This will be important to know when learning about arc flash because, in an arc flash, the circuit is completed through the air,
not just through wires.
This is because, even though air has insulating values, it has its limits. If there is enough voltage, the circuit can be completed
just by going though the air.
For example, with live parts at 72,500 volts, you must keep body parts and other grounded items more than two feet away to
avoid current flowing through you because at that high of voltage,
the circuit can be completed even through a foot of air.

How Shock Is Measured
Condition Resistance (ohms)
Dry Wet
Finger Touch 40,000 ‐ 1,000,000 4,000 ‐ 15,000
Hand Holding Wire 15,000 ‐ 50,000 3,000 ‐ 6,000
Finger Thumb Grasp 10,000 ‐ 30,000 2,000 ‐ 5,000
Hand Holding Pliers 5,000 ‐ 10,000 1,000 ‐ 3,000
Palm Touch 3,000 ‐ 8,000 1,000 ‐ 2,000
Hand around1 1/2 pipe 1,000 ‐ 3,000 500 ‐ 1,500
Hand Immersed ‐ 200 ‐ 500
Foot Immersed ‐ 100 ‐ 300
As you can see from this chart, wet, sweaty conditions can be much more dangerous than dry conditions because water and
sweat decrease the resistance to electricity, allowing more current to flow through the body when someone is shocked or
electrocuted.
It always makes good sense to stay away from energized parts, but especially so when conditions are wet.
This is why electricians are required to wear gloves and use special tools when working on electrical equipment. The proper
clothing and tools keep the resistance through their body high enough to keep from getting shocked.
Other factors other than water or sweat will determine the resistance of someone being shocked.

Resistance will often depend on the path of the circuit through the body. A shock from one finger to another finger on the
same hand will probably provide less resistance than a shock traveling from one hand to the other or from a hand to the
ground through a foot.
In any situation where the circuit has a chance to go through the heart, the dangers can be life-threatening.
As you’re looking over the chart, notice how the wet situations offer less resistance than the dry situations. This is because
current will flow through dirty water and sweat much more easily than through air and dry skin.
Also, grabbing a wire would be much more dangerous than just barely touching a wire because more of your skin would be in
contact with the wire.
Regular metal tools also increase the chance of getting shocked. This is why electricians often have specialized tools for
working on electrical equipment.
How to Avoid Shock Hazards
Do not work on energized (live) equipment
Stay away from electrical wires on the ground
Never open an electrical panel
Avoid working around water or wet locations
Keep work areas clean and tidy
The best way to keep from getting shocked is to stay away from electrical shock hazards.

Obviously you should never work on live or energized electrical equipment, not only because it is dangerous, but also
because you are not qualified to work on the equipment.
Another hazard involves live electrical wires in the wrong place. So if you see wires lying on the ground, do not go near them
and tell your supervisor immediately.
Since you will often have to work near electric panels, make sure to never open them. Opening the panel increases the
chances of getting shocked or setting off an arc flash.
Another hazard is water. Although sometimes it may be unavoidable, try to never work in wet areas that are near electrical
equipment.
Keeping your work area clean and organized can help you spot electrical hazards that you might otherwise miss in a messy
work area. If you need to clean a work area that is disorganized and dirty, be very careful so no unseen hazards will hurt you.
How to Avoid Shock Hazards
Never use a damaged outlet
Never use a damaged electrical cord
Never use a cord with the ground prong missing
Do not plug too many things into one outlet
Stay alert
Even when you are not working around high voltage equipment or electrical panel boxes, shock hazards still exist.
Damaged outlets should never be used. If you see a damaged outlet or suspect an outlet might be damaged, stop using it and
notify your supervisor immediately.
The same goes for cords and plugs. If you see an electrical cord that looks worn out, it might have exposed wires. Also plugs
that are damaged might not be properly grounded, increasing the chances of getting shocked.

Another possible hazard is having too many items plugged into the same outlet or on the same circuit breaker. Most often,
the circuit breaker will safely open the circuit, but the sudden loss of electricity to electrical equipment could still cause
injuries.
Above all, just stay alert. Always be on the lookout for hazards and be prepared to stop working, protect those around you,
and get help to take care of the situation as fast and as safely as you can.
Arc Flash
What Is An Arc Flash?
An arc flash is a short circuit through the air in an electrical panel box or any other
piece of energized electrical equipment. Air, as you have already learned, is normally
an insulator, but with a high enough voltage, a slipped tool, or a panel box that is
dirty, the circuit can be completed, causing a short.
When the short happens and the circuit is completed through the air, the air breaks down to where it offers little‐to‐no
resistance to the flow of electricity.
Remember, this is what a short circuit is. A short circuit will have almost zero resistance and will have very high levels of
current. The high current is what is responsible for the arc flash.
The tremendous amounts of energy released in an arc flash make for a very bright, very hot, and
very loud explosion.

Arc Flash vs. Safely Completed Circuits
Higher than normal currents
Now in a safely completed circuit, such as when a motor turns on a manufacturing line, the circuit is complete, just like in an
arc flash, but a safely completed circuit has a load on the circuit offering resistance.
So in a safely completed circuit, the resistance affects the current in the circuit, keeping the current under dangerously high
levels.
Think of a lamp plugged into the outlet of your house. When you turn it on, the circuit is completed, but the light bulb has
resistance, so the current stays within safe limits.
If you were to stick a paper clip in an outlet, the circuit will also be completed, but this time it will be a short circuit because
the metal paper clip offers very little resistance to the flow of electricity.
By the way, NEVER stick a paper clip into an electrical outlet. It is dangerous, and if you do it you will receive an electric shock
or worse.
High Voltage Short Circuit
A short circuit, as shown in this next video, does not have a load providing resistance. The arc that forms goes right through
the air with little‐to‐no resistance.
The same thing happens in an arc flash.
The circuit is completed straight through the air.
http://www.youtube.com/watch?v=PXiOQCRiSp0&feature=related
Or Jacob's Ladder_ 500kV Switch Opening - YouTube (360p) in Video file

Where Does An Arc Flash Occur?
Electrical panel box
Copper cables
Low voltage, high current
To understand how an arc flash occurs, lets create an imaginary arc flash.
To create an arc flash, a small piece of copper wire is placed between two of the wires coming into a three phase panel box.
When the power is turned on, the small metal wire quickly vaporizes because of the high current and allows the air to break
down between the two copper cables, decreasing the resistance and allowing dangerous levels of current to flow in a circuit
even after the small wire is gone.
The larger copper cables will also vaporize, adding to the explosive power and brightness of the arc flash.
Arc flashes can occur on any high voltage electrical equipment, not just in panel boxes.
Arc Flash Test Video
In this next video, you will see how scientists create arc flashes in order to study them.
View “Arc Flash PPE Laboratory Testing Video - YouTube (360p)” in Video file

What Causes An Arc Flash?
Slipped tools or hands
Falling parts
Dust, water, corrosion, oil
Animals
Sometimes there is no known cause
When arc flashes occur by accident, they can sometimes be caused much like the way they are made on purpose.
An accidental slip of a tool, a loose part, or even your hand touching live parts can provide the start the current needs to
jump from one cable to the next.
Loose connections in the electrical equipment, improper installation, and parts that break and fall are other possible
triggers.
Dust, water, impurities, contamination, corrosion, oil, and grease can also provide a starting route for the short circuit.
Even animals or bugs can get into electrical devices and start an arc flash.
Typically there is a reason for arc flash accidents, although we may not always know what it was.
The unpredictable nature of arc flash accidents is why it is so important to know about them and stay away from dangerous
situations.

What Happens During An Arc Flash
We have already mentioned some of the dangers of an arc flash,
but let’s cover them more fully now.
An arc flash is brighter than the sun, hotter than the sun, sends
metal pieces flying away from the explosion at over 700 miles per
hour, and is louder than a jet.
Bright Light
Skin damage
Blindness
The bright light from an arc flash can cause severe skin damage, although you might not notice it since your skin would
probably be burned so much from the extreme heat.
Your eyes, though, even if wearing safety glasses, can receive enough blinding light in that short instant that you will never
be able to see again.
Going blind is just the first of many injuries an arc flash can give you.

Hot Temperatures
Welding arc = 3,000° F (1648.89 °C)
Sun = 9000° F (4982.22 °C)
Arc Flash = 35,000° F (19426.67 °C)
When an arc flash occurs, it gets really hot, some of the highest temperatures known to man.
Just to show you how hot the 35,000 degrees Fahrenheit of an arc flash are, let’s look at a couple of items we know are hot.
The temperature of welding arc is 3000° F. That is hot enough to melt and fuse together metal.
The temperature of the Sun is 9000° F. That is hot enough for atomic fusion.
The temperature of an electrical arc flash, though, can reach 35,000° F. It is difficult to really understand how hot that is and
how destructive it can be, but luckily arc flashes don’t last very long.
But you can get severe burns from the heat of an arc flash even though it lasts only for a fraction of a second.
The chances of getting severely burned can be reduced by wearing the proper protective clothing. We will go over the
selection of personal protective clothing, or PPE, later in the training.
Large Explosion
Vaporized copper expands to 67,000 times its original size
Metal flies toward you at 700 miles per hour (1126.54 km per hour)
The intense heat from an arc flash can cause solid copper cables to change to liquid and then to vapor almost instantly.
When copper vaporizes, it expands to 67,000 times its original size, this leads to the large explosion ‐ a very large explosion.
The explosion creates a pressure wave sending shrapnel (such as equipment parts flying like an exploding grenade) hurling at
high speed (over 700 miles per hour).

Very Loud
You can lose your hearing
Ear plugs might not help
Since the explosion happens so fast, the quickly moving air can damage your ear drums, causing a worker near the blast to
become deaf…never being able to hear again.
Severe arc blasts will have a noise level of more than 140 decibels at a distance of two feet away.
Most ear plugs provide effective protection up to about 105 dB Regular ear plugs, then, do not provide adequate protection
from arc flash accidents.
Arc Flash/Arc Blast
They always occur together
An arc flash always causes an arc blast
You will often hear the terms arc flash and arc blast used together because they always happen together.
The bright light and high temperature is the arc flash. The explosion and the loud blast is the arc blast.
For this training, though, we will continue to use arc flash for the entire event: light, heat, sound, and explosion.

Arc Flash Videos
Let’s look at a couple of videos of actual arc flash accidents to see just how fast they can happen and how explosive they can
be.
View “Arc Flash Fatality Video.wmv - YouTube (360p)” is Video file
As you can see the doors are open on this energized equipment.
These circuit breakers are normally motorized. In most cases the doors are closed when opening and closing a breaker.
If the door must be open, the bus or bus bar, which is a thick strip of copper or aluminum that is used to carry very large
currents or distribute current to multiple devices within switchgear or other equipment, should be de‐energized before
working on it. The worker does not have the proper PPE to be working near exposed live equipment.
Notice the piece of test equipment on the floor. There must be a problem with the motor, and it looks like they are trying to
close the breaker manually.
The second worker, possibly the supervisor, gives the worker the OK to proceed just before the explosion.

Arc Flash Is Unpredictable
Every worker should assume the worst
Another item the test acknowledged is the highly unpredictable nature of arc flash accidents.
The report stated “Workers and equipment may be at risk from electrical arc, even at times when codes, standards, and
procedures are seemingly adequately addressed” meaning that even if everything is done right, an arc flash can still occur.
They also advised that “workers should ‘assume the worst’ and use available personal protective equipment.”
Approach boundaries
Flash protection boundary
Limited approach boundary
Restricted approach boundary
Prohibited approach boundary
The shock boundaries are calculated based on the amount of voltage being supplied to the equipment. The flash
protection boundary requires more data.
While the amount of current and the how long the arc flash lasts are the two big factors to consider when figuring out
how severe an arc flash will be, how bad you get hurt also depends on how close you are to it.
Just a few inches could be the difference between life and death when close to an arc flash.
If a very large arc flash accident happens and no one is near it, no one gets hurt. This is why arc flash boundaries are so
important.
The four common boundaries around electrical hazards are the flash protection boundary, the limited approach boundary,
the restricted approach boundary, and the prohibited approach boundary.

Arc Flash Boundary Table
Specific Restricted Areas and Boundaries
for the Company Involved
This will change for each company and will
be 5 to 10 minutes long, or will be deleted if
the company requests so.

Calculating Arc Flash Hazards
Available current and volts
Time
Distance
PPE
We have already mentioned four things that contribute to how bad you are hurt in an arc flash accident: the available current
and voltage, how long the arc flash lasts, how far away you are from the arc flash, and what type of personal protective
equipment, or PPE, you are wearing.
You are responsible for making sure you are wearing the right PPE, but the arc flash boundaries will already be calculated for
you and put on a label.
The intensity of the arc flash can range from a small flash of light to an explosion. The available current and how long it takes
for the short circuit to be broken are the two factors used in calculating the flash protection boundary.
Just A Fraction of A Second
Arc flashes don’t last very long, but they are still powerful enough to kill
Since alternating current is what manufacturing companies use to power most of their equipment, arc flash incidents are
sometimes measured in cycles.
If a company is using 480‐volt, three‐phase AC at 60‐hertz and the short circuit stays complete for six cycles, then it lasted
one‐tenth of a second.
This is easily enough time to allow an explosion large enough to kill you even if you are up to 10 feet away.
So just a tiny amount of time, then, is needed for an arc flash to cause horrible injuries to affected workers near a piece of
electrical equipment.

Personal Protective Equipment (PPE)
You can see how important clothing is to protecting your body from an arc flash by taking a piece of fabric, say from a t‐shirt,
and putting it over your finger and touching it quickly to a hot iron. You will probably not feel any heat since you touched it
for just a fraction of a second.
Of course if you held your finger there for more than a second or two your finger would get burned and blister, but this is not
what happens in an arc flash.
In an arc flash, the temperature is much higher, but hopefully lasts only a short amount of time, sort of like quickly touching a
hot iron – only at tens of thousands of degrees for the arc flash instead of a couple of hundred of degrees for the iron.
When this level of heat is involved for such a short amount of time, the part of clothing or skin that does come in contact
with the heat will be completely destroyed. Hopefully it will be your protective equipment and not your skin that is destroyed
in the arc flash accident.
This is one of the reasons why wearing personal protective clothing is so important. If something is going to get burned and
destroyed, you want it to be your clothing and not your skin.
Calories
Calories measure energy
1.2 calories per centimeter squared
Same as holding your finger over the flame of a lighter
When dealing with personal protective equipment, or PPE, you will often hear the word calorie.
This “calorie” is the same you are used to hearing when talking about food.
Its formal definition is “the energy required to raise one gram of water one degree Celsius at one atmosphere” or the amount
of energy it takes to heat up a few drops of water one degree.

You will get second‐degree burns at 1.2 calories per centimeter squared per second.
This might be a little hard to grasp, but think of it this way: One calorie per centimeter squared per second, is like holding
your finger over the tip of the flame of a cigarette lighter for one second.
This could easily give you a second degree burn.
When You Need To Wear PPE
If you…
• Open electrical panels that have energized (live) conductors inside
• Work on, install, or maintain energized conductors or equipment
• Stand within about 4 ft. of an open electrical panel…you need to be qualified and wear the proper PPE
Let’s look at some situations where you would need to wear PPE for arc flash hazards.
The first is if you need to open electrical panels that have energized or live conductors inside.
As an affected employee, you will not have to do this.
You would also have to wear the right PPE if you work on, install, or maintain energized conductors or electrical equipment.
Again, only qualified employees need to do this type of work. As an affected employee, you will not do this type of work.
What about the next one? Standing within four feet of an open electrical panel.
Now you might be doing this, so although you will not be working on live equipment, you still might need to work in an area
that will require you to wear arc flash personal protective equipment.

What PPE Do I Need To Wear?
Clothing, Voltage‐rated gloves, Face shields, Full protection suits, Insulated blankets, Safety glasses and Ear plugs.
Personal protective clothing includes not just cotton clothing and flame resistance clothing, but also includes voltage rated
gloves, face shields, full‐coverage flash suits, and insulated blankets.
Remember that any time you cross the arc flash protection boundary, you need to wear the proper PPE. This does not mean
you will need to dress up in the full‐coverage flash suit every time you cross the flash protection boundary, but you will need
some level of protection.
When you go to work, you need to make sure to always wear cotton clothing. Materials like nylon or acetate will ignite and
melt on your skin if an arc flash occurs, causing severe burns.
You should also always wear safety glasses and ear plugs if you are working near moving parts.
Let’s look over some of the different levels of protection to see what you would need to wear in different situations.
PPE Care and Inspection
The employee wearing the protective clothing and PPE must inspect them each time they need to wear them.
If you notice any damage to any of the PPE, report it immediately. Do not use the damaged PPE and do not enter any flash
protection boundaries until the PPE is repaired or replaced.
Remember, if you are required to wear PPE, it is your responsibility to make sure it is in safe working order.
Since you will probably not be trained in how to inspect PPE properly, you will have to ask for help if you need to inspect arc
rated PPE.

Appropriate Tools for Safe Working
Tools are often made of metal, and metal is a good conductor.
This makes metal tools potentially very dangerous around electrical hazards, unless the tools are properly insulated.
Insulated tools, then, must be used whenever working on energized electrical equipment.
Here is a picture of some insulated tools for working on live parts. Notice the double triangle symbol to show workers that
this is an insulated screwdriver.
Since you will not be working on energized equipment, you will not need to use insulated tools, but you should know what
they look like since you might see them on the job.

Working Safely
Look for labels
Look for unlabeled hazards
Assume all equipment is live and energized
Look for lockouts and lock out box in control room
Wear the right clothing to work
Use PPE when needed
• Now that you have a good idea about what to look for when you see an arc flash hazard label, let’s go through some tips
to make sure you continue to work safely around these hazards.
• Always be on the lookout for hazards, whether they are labeled or not.
• Assume that all equipment is fully energized with electricity. Do not think that just because someone is working around an
electrical hazard that they have de-energized the equipment.
• Also be aware of any equipment that is locked out or tagged out. Locking out and tagging out a machine makes sure no
one tries to energize a piece of equipment while someone else is working on it.
• If you see a tag like the one shown in the picture, do not try to remove it. Only the person who locked out the machine
has the authority to turn it back on.
• Also, wear the right clothing to work. PPE will be provided by the employer, but you should wear your own non‐melting
clothing, work boots, and safety glasses.

What To Do If An Arc Flash Occurs
To someone else
Stay away from the explosion
Get help
Stay calm
To you
Get away from the explosion
Get help
Stay calm
• If you are near an arc flash accident and see someone who is injured, don’t follow your instincts to rush in and save them.
You might set off another arc flash and be killed. You will not be able to help if you are dead.
• What you should do is get help right away. The time it takes for a critically injured person to get help is crucial in helping
them survive the accident.
• Let other workers know about the accident and get someone to call 911. If you are not trained in giving medical attention,
do not try. Wait until someone who is trained shows up to help.
• It you are the one who is injured in an arc flash accident, try to get away and get help immediately. What will most likely
happen is that you will automatically try to get away if you are still conscious and will probably not remember much.
• Also, stay calm. Hopefully you will be wearing the right protective clothing and the proper PPE.
• If not, you might be in the 95 percent of all accidents that could have been prevented by working safety and wearing the
right protection.

Summary
• Electrocution is a shock that kills
• Pure water is an insulator, sweat is a conductor
• Arc flashes are short circuits with low resistance and high current
• Arc flash labels will help you stay away and wear the right PPE
• Thanks for being so attentive today. To quickly summarize some of the things you have learned today, let’s go through a
few final points.
• Electricity is powerful and can be dangerous. Be careful around it.
• Electrocutions are shocks that kill you. Stay away from shock hazards, especially when you are sweating, since sweat is a
conductor of electricity even though pure water is not.
• Arc flashes are short circuits that happen when no load or resistance is in a circuit and the circuit is completed through
the air, causing an explosion. The explosion is bright, loud, and hot.
• Since an arc flash’s intensity is determined by the available current and how long it lasts, arc flash hazard studies are done
to figure out safety boundaries and PPE levels for each hazard.
• The labels will be placed where you can see them so you can stay away or wear the right PPE so that the PPE is destroyed
in an arc flash instead of your skin.
• Always keep in mind that no equipment is so important and no service so urgent that we cannot take the time to do
the job safely.

• Always keep in mind that no equipment is so important and no service so urgent that we cannot take the time to do
the job safely.
• Always verify your test instruments.
• Isolate power personally if repair is necessary.
• Verify that no voltage is present before making any repairs.
• Think about what you are testing and what you expect to find. Random probing with the test instruments can cause
serious mistakes for personnel and equipment.
• Be aware of the mechanical dangers. What may happen when the machine is energized either normally or
abnormally?
• Be certain any temporary work is absolutely safe.
• Verify safe working order after completion. Remove all test jumpers and device defeats. Check all safety circuits before
returning the machine to normal service.
• Use electrical “SAFTEY HOOK” to remove any person from electrical source and NEVER EVER TRY TO REMOVE A
PERSON BY HAND or REMOVE ELECTICAL SOURCE BY HAND.

Basic Test Equipment
Test instruments come in various types, shapes and sizes. The most common types of volt-ohm-meters are grouped in two
categories, analog and digital. There is also a type of ohmmeter called a meg-ohm-meter that will be discussed later in this
chapter.
The Analog Volt-Ohm-Meter (VOM)
Troubleshooting with an Analog VOM
The analog VOM is frequently used in conventional trouble-shooting but is becoming more
obsolete due to digital multi-meters. The VOM can tell the trouble-shooter if voltage is
present or not, and can also tell how much is present. At times this additional information
can be helpful. There are some concerns to be aware of when using test instruments such as
the VOM.
Meter Damage - It is easy to overlook the range and function selected on a VOM. If the
wrong range or function is selected, incorrect readings and/or meter destruction can occur.
Calibration Errors - Most instruments of this type need periodic calibration. An instrument
that is out of calibration can cause lost time and wasted efforts due to the incorrect readings.
Expense - Initial cost of industrial quality VOM's is quite high. As with any precision
instrument, extra care must be taken to protect it.

The Digital Multi-Meter (DMM)
Digital multi-meters (DMM) have generally replaced the analog-type multimeter (VOM) as the test
device of choice for maintainers because they are easier to read, are often more compact and have
greater accuracy. The DMM performs all standard VOM measurement functions of a-c and d-c. Some
offer frequency and temperature measurement. Many have such features as peak-hold display that
provides short-term memory for capturing the peak value of transient signals as well as audible and
visual indications for continuity testing and level detection.
To compare these two types of multi-meters, let us examine their pros and cons in more detail:
• Ease of reading. One of the greatest problems with an analog meter is the errors that occur due to
the human factor when reading off the value from the many different scales. The thin analog
needle against a calibrated scale is similar to the hands of a clock against the number scale
indicating the hours.
When you look at an analog clock, you have to determine where the hands are, which number the hand is nearest to, and
so on. With a digital clock, however, the time is read directly from a display. With the analog meter, the decoding of the scale
is necessary, while the digital multimeter displays the magnitude, polarity (+ or -), and the units (V, A, or Α) on typically a four-
or five-digit readout. A disadvantage of the digital multimeter is its slow response to display the amount on the readout once
it has been connected in the circuit. To compensate for this disadvantage, most DMMs have a bar graph display below the
digital readout, as shown in Fig. 2, showing the magnitude of the measured quantity using more or less
bars. A bar graph reading is updated 30 times per second while the digital display is updated only 4 times per second.

The bar graph is used when quickly changing signals cause the digital display to flash or when there is a change in the circuit
that is too rapid for the digital display to detect. For example, a contact’s resistance changes momentarily from zero to infinity
when a contact “bounces”. A DMM cannot indicate contact bounce because the digital display requires more than 250
milliseconds to update.
A DMM set to measure voltage may display a reading before the leads are connected to a powered circuit. This is known as a
“ghost voltage” and is produced by magnetic fields, fluorescent lights and such which may be in close proximity. These
voltages enter the meter through the open test leads which act as antennae. These voltages are very low and will not damage
a meter but can be confusing as to their source.
• Accuracy - DMMs are typically accurate to 0.01 % and have no need for a zero-ohms adjustment. Returning to the example
of the analog and digital clock, a person reading the time from the traditional analog clock would say that the time is
almost 12:30. The wearer of the digital watch, however, will be totally specific and give the time as 12:27. Similarly, an
analog reading on a meter of about 7 V becomes 7.15 V with the far more accurate DMM.
• Price - Digital meters have complicated internal circuitry that is why the digital readout meters usually have a more
expensive price tag than the analog readout multi-meters.
Fig. 2

When troubleshooting with the digital multimeter, the maintainer is able to “see” the situation and the problem within the
circuit or system. Fig. 3 illustrates a typical auto ranging digital multimeter. Of course for the meter to be of any use it must
first be connected to the circuit or device to be tested. Both leads, one red and the other black, must be inserted into the
correct meter lead jacks. The black lead is connected to the meter jack marked COM or common. It is usually the lower right
jack as in this illustration. (Be aware that not every meter has the same jack configuration.) The red lead is connected to
either of the appropriate jacks depending on what the maintainer wants to measure; ohms, volts or amperes. The two jacks
on the left are utilized when measuring current, either in the 300mA or the 10 ampere range.
The display shows other functions as well.
• Low battery indicator
• Annunciators show what is being measured (volts, ohms, amps, etc.)
• Autopolarity indicates negative readings with a minus sign when the leads are connected incorrectly without any damage
• Auto ranging automatically selects proper measurement range
• One selector switch makes it easy to select measurement functions
• Overload protection prevents damage to the meter and the circuit, and protects the user.
Fig. 3

Measuring resistance – Fig. 4 shows the steps that should be followed when measuring resistance. Remember that
resistance measurements are carried out without the power being applied to the component under test, and resistance
values can vary by as much as 20% due to the tolerance of certain resistors. Do not be misled if your meter reading is slightly
different from the color band on the resistor. If a resistor’s value is off and exceeds the tolerance, the resistor should be
replaced. A resistor will rarely short, but typically will open. If a resistor does open, the DMM display will flash on and off or
display OL (open line) because the resistor has an infinite resistance.
1. Turn off power to the circuit
2. Select resistance Ω
3. Plug the black test lead into the COM jack and the red test lead into the Ω jack
4. Connect the probe tips across the component or portion of the circuit for which you
want to determine the resistance
5. View the reading and be sure to note the unit of measure, Ω, KΩ, MΩ, etc.

Measuring voltage – Fig. 5 shows the steps that should be followed when measuring voltage. The measurement of both
voltage and resistance is where the DMM finds its greatest utilization. For voltage and resistance measurement, the red lead
is inserted into the V – Ω (volt or ohm) meter jack.
1. Select volts AC (V~), volts DC (V---), mvolts (V---) as desired
2. Plug the black test lead into the COM jack and the red test lead into the V jack
3. Touch the probe tips to the circuit across a load or power source as shown (parallel to the
circuit to be tested)
4. View the reading being sure to note the unit of measure
Note: For DC readings of the correct polarity (+ or -), touch the red test probe to the positive
side of the circuit, and the black test probe to the negative side of the circuit ground. If you
reverse the connections, a DMM with auto-polarity will merely display a minus sign indicating
negative polarity. With an analog meter you risk damaging the meter.

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