The document outlines essential information regarding electrical safety, including common voltage levels, the effects of electric current on the human body, and the proper measures for rescue and first aid. It describes the dangers of electrical shock, the importance of proper grounding, and the role of safety devices such as fuses and circuit breakers in preventing overcurrent situations. Additionally, it emphasizes safety precautions when working with electrical circuits and equipment, and the need for regular maintenance and inspections to ensure safe operation.

2.  Common Voltages for Residential and
Industrial Applications
◦ 120V, 240V, 480V
 High Voltage – voltages exceeding 600V
 Low Voltage – voltages between 24V – 600V
 Safety Low Voltage – voltages lower than 24V

3.  The extent of electrical injury is determined by:
◦ Amount of current that passes through your body
◦ The path it takes
◦ The length of time you are in contact with the current
 Electrical shock occurs when your body becomes
part of an electrical circuit
◦ Contact with both the hot (L1&L2) conductors at the
same time
◦ Contacting a current-carrying conductor and ground
◦ Contacting hot equipment body and ground

4.  Effects of electric current through the human
body
 1mA or less – no sensation, not felt
 1-8mA - shock is felt but not painful
 8-15mA - painful shock but muscular
control not lost
 15-20mA - painful, muscular control is lost
 20-50mA - painful, severe muscular
contractions
 50-200mA - possible ventricular
fibrillation,muscular contraction, nerve damage
 Over 200mA - severe burns and severe
muscular contractions

5.  Shock Current
Path
◦ Why have it a
ground free lines?

6.  Effects of electric current through the human body
◦ 1mA or less – no sensation, not felt
◦ 1-8mA - shock is felt but not
painful
◦ 8-15mA -
painful shock but muscular control
not
lost
◦ 15-20mA - painful, muscular control
is lost
◦ 20-50mA - painful, severe muscular
contractions
◦ 50-200mA - possible ventricular
fibrillation,
muscular contraction, nerve damage
◦ Over 200mA - severe burns and severe
muscular
contractions

7.  Typical Electrical Resistance
◦ Dry wood – 200K – 200MΩ/inch
◦ Damp wood - 2K – 100Ω/inch
◦ No. 10 Cu wire- 1Ω/100ft
Human Body
◦ Dry skin - 100K – 500KΩ
◦ Wet skin - down to 1KΩ

8.  Most fatal electrical shocks occurs when current flows
through or near the heart
◦ A 100mA of current flowing for 1/3 of a second can cause a
ventricular fibrillation which usually result in death
◦ Fibrillation is the rapid, irregular, and unsynchronized
contraction of muscle fibers, usually heart muscles
 If heart stops because of chest muscle contraction
and not result to fibrillation, heart massage, mouth to
mouth resuscitation and other survival procedures
must be administered within 3-4 minutes for
possible restoration of normal heart action and
circulation

10.  Effects of non-lethal amounts of current
passing through the body
◦ Mild tingling sensation
◦ Severe pain
◦ Muscle contraction
◦ Burns
◦ Internal hemorrhage – internal bleeding
◦ Respiratory problems
◦ Secondary accidents – mauntog dahil sa gulat

11.  Rescue and first aid measures:
◦ Do not touch the victim when while he is still in
contact with the current.
◦ Shut-off power or push the victim with a dry non
conductive material
◦ Call medical assistance immediately

12.  Avoid contact with energized circuits.
◦ Insulate / isolate current carrying parts of an electric
tool/equipment by rubber or plastic
◦ Wires with damaged insulation should be replaced. For
temporary repair, wrapped with electrical tape
◦ Shut-off power/de-energized circuit involve during
maintenance, repair, set-up or any servicing done on
electrically powered devices
◦ Since it may not always possible to de-energize all nearby
circuits, you should know which circuit is energized and not
before starting the job. If possible, place a rubber/plastic
shield over around exposed energized parts.
◦ Make sure you know what is behind/under the material you
are drilling or cutting with a power tool. Consult an
electrical blue print to verify or consult electrical
department to be sure no wiring is near where you must
drill/cut.

13.  Electrical circuits are designed to operate below or at the
maximum rated current levels
◦ Overcurrent condition – when the maximum current of the circuit
is exceeded by overloading the circuit or having a short circuit
between two live conductors
 Fuses and Circuit Breakers – safety devices used for
overcurrent protection. They open the circuit once
overloads and short circuit occurs.
◦ Blown fuse / tripped circuit breaker indicates overcurrent occurs
and something is wrong in the circuit.
◦ Do not attemp to re-energize circuit unless the problem is
corrected
◦ Electrical problem correction should be done only by a trained
personnel
◦ Fuses and circuit breakers are not protection for shocks because
they only react at the current above its rating, and they do not
react quickly enough.

14.  MCCB - Molded Case Circuit Breaker
 Magnetic type or Instantaneous
Detects short circuit fault
 Thermal type or Inverse Time
-The higher the current the faster it clears a fault
 Residual Current Circuit Breaker
+GFCI
 Non time delay fuse - Blows after exceeding its
rating
 Dual Element Time Delay Fuse - Both thermal &
instantaneous features allows motor starting

15.  MCCB -
(Total load in
amperes X 800%)

16.  Earth Leakage
Circuit Breaker

17.  Total load in
Amperes X 300%
Dual Element
Time Delay fuse
Total load in
Amperes X 175%

18. -NEC states that
100 watts shall be
the maximum load
for each lighting
outlet.

19.  Ground – conducting connection between an
electrical circuit and earth
◦ Proper grounding helps keep voltages confined by
avoiding dangerous differences in voltage levels between
two conducting surfaces.
 In ground-neutral power system, the neutral
conductor is connected to earth ground
– circuit ground
 Ground faults - an accidental connection
between a circuit conductor and the earth

20.  Method of shock protection for both portable and
stationary electrical equipments.
 It uses an additional wire (green) that is
connected to the body, frame, case, handle, or
other exposed metal parts of the equipment to
the ground.
◦ Ground wire
 It provides an alternate path of current in case
the hot wire touch the body/case of an
equipment causing a short circuit to the neutral
wire thus producing hi current to blow the fuse.

22.  GROUND FAULT CIRCUIT INTERRUPTER (GFCI)
◦ Detects an imbalance current between
hot and neutral conductor.
When imbalance occurs, it immediately
opens the circuit before the fault current
can reach the hazardous level
◦ Reacts only to ground faults but
not to short circuit.

23.  Flammable materials and explosive
atmosphere exist.
◦ Wirings are explosion proof
◦ Uses safety low voltage (24V and below)
◦ Equipments are explosion proof capable of
containing an explosion within itself

24.  Should always have equipment grounding
 Usually uses double insulation
◦ Additional, independent insulation
◦ Plastic housing / inner lining with metal exteriors

25.  Consider all electrical circuits ENERGIZED
AND DANGEROUS until you are certain you
are not.
 Check your work area for wet surfaces
 Do not wear rings, watches and other metal
jewelry items when working near electrical
circuits
 Do not use metal ladders or uninsulated
metal tools and hand lamps
 Use only EXPLOSION PROOF tools, lamps, and
equipments in hazardous locations

26.  Shut off and lock out power before repairing a
circuit, either electrical or mechanical repair near
energized circuit
 Examine all electrical tools and equipments for
any signs of damage or deterioration
 Do not energize or deenergize any electrical
circuits unless:
◦ You are authorized to do so
◦ You are familiar with the circuit controls and you know
what is connected in the circuit.
◦ All other workers are in danger unless they have been
specifically notified when power is about to be turned
on/off.

27.  System ground resistance - from all neutral points to
earth ground
◦ Not exceeding 25 ohms
◦ Should be check annually
 Equipment ground resistance - from all exposed
non-current-carrying metal parts to earth ground
◦ Not exceeding 25 ohms
◦ Should be check annually
 Insulation resistance between two hot conductor
◦ 50 Mega ohms
 Insulation resistance between hot and neutral
conductor, and hot and green conductor
◦ 50 Mega ohms

28.  GFCI
◦ Should be check also annually for good operation
◦ Test button is pressed and reset when functioning properly.
 Service Entrance
◦ Check the voltage, conductors, insulation, terminations, to assure
they there are no cracks, burns, or any sign of damage
 Distribution panel
◦ Check circuit breaker for any build up of dirt or surface
contamination
◦ Check circuit breakers for crack terminals
◦ Exercise circuit breakers by performing several operation on
switch handle
◦ Check fuse terminals, and holder for discoloration caused by heat.