A 3-phase motor starter contains power and control components to safely start and stop a 3-phase motor. The power components include line stabs to connect to the power source, a breaker to safely disconnect power, a main contactor to switch power to the motor, and overloads to protect from overloads. The control components provide low-voltage control power and signals to operate the main contactor and safely start and stop the motor. Understanding each component and how they work together is important for safely locking out and working on a motor starter.

1. 3 Phase Motors and Motor Starters
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2. Main Menu
• To safely lockout and work on a 480 VAC motor starter you will need
to know:
– Part 1: How a motor works
– Part 2: The components of the power circuit and how they work
– Part 3: The components of the control circuit and how they work
What do I need to know?•
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3. Part 1: Motors
• To name the parts of a 480vac motor
• To explain induction
• To explain how a motor operates
In This Section, You Will Learn :
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4. The Parts of a 3 Phase
Squirrel Cage Motor
• The motor has two primary parts:
– The rotor
• This consists of a “Squirrel Cage” assembly, the shaft, the
bearings, and the cooling fan
– The stator
• This consists of the field windings, the casing and footing, and
the end bells and bearing supports
– It is often referred to as an “Induction Motor”
• For the purposes of this discussion, the example motor will be a
3 Phase, 480 VAC, Totally Enclosed Fan Cooled (TEFC) motor
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5. The Rotor
– They are made out of a material that is easy to generate a magnetic field
in
– There are typically more than shown in the drawing
– The gaps are filled with resin, aluminum, or other light material
– The shaft is typically bonded into the assembly
– When the plates are arranged, and before they are filled in, they
resemble a squirrel cage treadmill
• This is why they are called squirrel cage motors
– The shaft will have ball bearings on either end, and a cooling fan on the
non-drive end
• The rotor is assembled out of stamped metal plates arranged
radially around the shaft
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6. The Stator
– The windings are arranged into three phases
– There is typically a small box attached for wiring
– There is a method for mounting the motor built in
– There is a fan cover enclosing the fan
• The stator consists of a set of coils (windings) inserted into a
frame, end bells with bearing supports, and mounting and
connection arrangements
Windings End Bell Bearing Support
Wiring Enclosure
(peckerhead)
Footing
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7. The Motor Assembly
– This means that the internal parts are sealed from the weather
and the atmosphere
• The motor assembly is TEFC (totally enclosed fan cooled)
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8. The Motor Nameplate
– The nameplate will have various information
• The catalog number
• The Horsepower
• The Rated Amps (and Full Load Amps)
• The Rated Voltage
• NEMA and rating codes
• Sometimes, the Bearing Numbers
• The Frame Designation
– The motor should be swappable with any motor with an
identical frame number (theoretically)
• Other miscellaneous information
• The motor will have a nameplate
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9. Induction
– Three things are required for induction:
• Relative Motion
• A Magnetic Field, or an electrical current (which creates it’s
own magnetic field)
• A Conductor
• Induction is the process of inducing a magnetic field using current
flow, or inducing a current flow using a magnetic field
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10. Inducing Current
– This is the principle by which generators, transformers, and
motors work
• By dragging a magnetic field along a conductor, all three
conditions will be met, and a current will be induced
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11. Inducing a Magnetic Field
– By running an electrical current through a conductor, a magnetic
field will be induced
• The motion is provided by the electrical current
• The field will be created, but does not move with the current,
or there would be no relative motion
• Instead, as the current increases, the field expands (gets
larger, and therefore stronger)
• Once the current has risen to it’s maximum value, so does the
field strength
• The process will work in reverse
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12. Alternating Current Field Induction
– This will provide alternating North/South magnetic fields
• By using alternating current, the field can be made to expand and
contract
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13. Motor Field Windings
– This is accomplished by using three fields (the three phases),
spaced 120° apart
• The winding field requires rotation to create the initial relative
motion that induces the rotor field
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14. Explaining Field Rotation
• At point 1, the A field is most positive, creating a strong North field in the A phase windings
– Both B and C phases have weaker South fields, but added together will equal the opposite of the A
phase field
• At point 2, the B phase has the strong North field, while C and A have the south fields
• At point 3, the C phase has the strong North field, while A and B have the south fields
• By repeating this pattern, the field rotates clockwise around the windings, creating a continuously
rotating magnetic field
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15. Rotor Operation
– The current flowing through the motor stator windings
creates a rotating magnetic field
– This field then sweeps across the rotor squirrel cage
assembly, inducing current flow around the rotor
– This current flow then induces another magnetic field
in the rotor
– The magnetic field in the rotor “couples” with the
magnetic field created by the windings, and the rotor is
“swept” along
– Note that the rotor cannot rotate as fast as the winding
field, or there would be no relative motion between
the windings and the rotor to induce the rotor field
• This is why a motor RPM will always be less than the line frequency
multiplied by 60
– Frequency = Cycles per sec (EX: 60 cycles/sec)
– RPM = Rotations per min (EX: 3600 RPM (R/Min))
– Frequency = RPM / 60 (EX: 3600 R/Min = 60 R/Sec)
• An induction motor works using magnetic induction
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16. Motor Wiring
– This is to give the capability of using the motor in low voltage (230
VAC) high current, or high voltage (480 VAC) low current
applications
– These are referred to as “wye” or “delta” windings
– The windings are not physically built like the diagram
• The diagram indicates how they are connected only
– Check the motor nameplate and documentation to see how to
properly connect the winding leads for the appropriate
configuration
• Motors frequently come with the capability of connecting the
windings more than one way
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17. Current Flow
– When A phase is North, current will be flowing from A to B&C
– When B phase is North, current will be flowing from B to A&C
– When C phase is North, current will be flowing from C to A&B
– No matter where the time is on the sine wave, A+B+C always
equals 0
– This means that the center point of the wye winding can be
connected to ground if necessary
• Since this center point is equal to A+B+C, and A+B+C always equals 0, then
there should never be any voltage present at the center point
• Note that in either configuration all three phases are connected to
each other
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18. Phase Rotation
– The rotation direction is governed by the driven equipment
requirements
• A squirrel cage motor will work equally well in either direction
– This may not be true of other types of motors
– Phase rotation is controlled by which phase is connected to which
lead
• After connecting a motor, bump it (start it very briefly) to
determine the direction of rotation
• If it is rotating in the wrong direction, reverse any two leads to
reverse the rotation
• Phase rotation refers to whether the phases are rotating
clockwise or counterclockwise
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19. Inrush Current
– This means that current flow will be very high
• It will last until the rotor field is established, and the driven
equipment is up to speed (doing work)
– This is referred to as “Inrush Current”
• When the motor is first started, for a very brief time while the rotor
field is being induced, there will be almost no resistance to
current flow
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20. Short Cycling
– This is referred to as “short cycling”
– When short cycling occurs, average current flows will be higher
than normal, and can quickly overheat the wiring and windings
• This is why motor overloads are installed in the power wiring
of a motor starter
• If problems occur in the starter control wiring, the starter can
start/stop the motor several times very quickly
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21. Part 1 Quiz Q1
• Name the major parts of the motor rotor
– The squirrel cage assembly
– The shaft
– The bearings
– The cooling fan
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22. Part 1 Quiz Q2
• Name the major parts of the motor stator
– The windings
– The case and footings
– The end bells and bearing supports
– The cooling fan cover
– The wiring enclosure (peckerhead)
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23. Part 1 Quiz Q3
• Name several important pieces of information
on the nameplate
– Horsepower
– Rated Amps
– Rated Voltage
– RPM
– The Frame Number
– NEMA codes and classes
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24. Part 1 Quiz Q4
• What does TEFC mean?
– Totally enclosed fan cooled
• Can a TEFC motor be used outdoors?
– Yes
• Can it be used in an explosive atmosphere?
– Yes
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25. Part 1 Quiz Q5
• What three things are required to induce
electrical current?
– Relative Motion
– Magnetic Field
– Conductor
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26. Part 1 Quiz Q6
• What three things are required to induce a
magnetic field?
– Relative Motion
– Electrical Current
– Conductor
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27. Part 1 Quiz Q7
• What happens to a magnetic field when the
current increases?
– It gets stronger and larger
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28. Part 1 Quiz Q8
• What causes the field to rotate in a motor?
– Three phases spaced 120° apart
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29. Part 1 Quiz Q9
• What are the two types of windings commonly
found on a motor?
– Delta and Wye
• How do you figure out how to connect the leads
for Delta and Wye?
– Check the documentation
• What are the uses of Delta and Wye?
– Low Voltage High Current and High Voltage Low
Current
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30. Part 1 Quiz Q10
• What does phase rotation control?
– Direction of rotation
• How do you reverse it?
– Swap any two power leads
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31. Part 1 Quiz Q11
• What is inrush current?
– High currents developed when first starting a
motor
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32. Part 1 Quiz Q12
• What is short cycling?
– Repeated rapid starting/stopping of a motor
• Why is this a problem
– It creates a very high average current which
rapidly overheats the power circuits and windings
• What prevents this from damaging the wiring
– Overloads installed in the power circuits
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33. Part 2: Power Wiring
• To name the parts of a 480vac motor starter power circuits
• To explain the function of each part
• To explain how the parts are connected
In This Section, You Will Learn :
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34. Parts of a 480 VAC Motor Starter
• For the purposes of this training, a
motor starter with a Hand/Off/Remote
(HOR) switch, local Run/Stop indicators,
and a remote Start/Stop station will be
used.
– Some starters will be
simpler, while other
starters can be much
more elaborate
• To safely lockout a 480 VAC motor
starter, you have to understand the
components and how they work
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35. Terminology: Inputs and Outputs
– It is sometimes referred to as the “High” side.
– On transformers it is frequently marked “H”.
• The output side of an electrical device is referred to as the
“Load” side.
– It is sometimes referred to as the “Low” side.
– On control transformers it is frequently marked “X”.
• When a breaker or switch is on, it is referred to as “Closed”
or “Energized.
– Indicator lights are usually red when equipment is energized (Red
= danger).
• When a breaker or switch is off, it is referred to as “Open”
or “De-energized.
– Indicator lights are usually green when equipment is de-energized
The Input side of an electrical device is referred to as the “Line”
or “Power” side.
•
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36. The Starter Enclosure
– It is sometimes referred to as a “Can” or a “Bucket”
– It includes a door, indicators, and switches
– The door is interlocked so it cannot be opened without
opening the breaker (securing power)
– The door is secured by a quarter turn screw, or a bolt
– The enclosure contains both power components and
wiring and control components and wiring
– The power components and wiring deliver power to
the load, in this example a 480 VAC three phase motor
– Control components and wiring provide the controls
for starting and stopping the motor, and in this
example are 120 VAC
• The starter enclosure is the metal box that the starter assembly is
contained in.
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37. Enclosure Identification
Quarter Turn Locking
Screws
Safety Interlocks
Breaker Handle
Enclosure
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38. The Line Stabs
– Stabs must NEVER be connected or disconnected while the
breaker is under load.
– The breaker MUST be locked out prior to connecting or
disconnecting a stab.
– Stabs allow for easy removal of the bucket without having to
secure buss power
– Power stabs are wired directly to the line side of the breaker
– If you have not been trained on how to remove a bucket, do
not attempt to do so
• “Line” or “Power” Stabs are disconnection devices designed to
connect the breaker wiring to the buss without having to secure
the power to the buss
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39. Line Stab Identification
480 VAC 3 Phase buss
(Behind Plastic Safety Shield)
A B C
Wires to Line Side of Breaker
symbol
Output (load) StabsLine Stabs Plug In Here
Enclosure Latch
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40. The Breaker
– It can do this because it has been designed to “break” the
electrical arcing that occurs when it opens
– It is NOT designed to close into a load (it is not a switch). The
equipment controls MUST be in the off position prior to opening
or closing a breaker.
– It has a rating marked on it for the maximum amperage it is
designed for
– Generally, the breaker switch is closest to the load side when the
breaker is open (off)
– The breaker switch will be in the middle if the breaker has tripped
– To reset a tripped breaker, correct the condition which caused the
trip, fully open the breaker, then close the breaker
• The breaker is a disconnect device designed to open under load,
when excess current is sensed (preventing electrical fires)
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41. Breaker Identification
Line (High) Side Wires attach here (Behind Cardboard Shield)
Breaker Switch (“3” indicates this breaker is rated at 3 amps,
Down position Indicates Breaker is Open/Off)
Load (Low) Side Wires Attach Here
Load (Low) Side Wires
Linkage Attaches to Breaker Handle on Door
symbol
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42. The Main Contactor
– When control voltage is delivered to the main contactor coil, the
armature closes the contacts
– The line side of the main contactor is connected to the load side
of the breaker
– Power for the control circuits is typically tapped from two of the
three phases on the line side of the main contactor, and sent to
the line side of the control transformer (more on this later)
• The main contactor is essentially a large 3 phase
solenoid relay switch
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43. Main Contactor Demonstration
Symbol
Turn ON
Use Button to
Demonstrate
Contactor Operation
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44. Main Contactor Demonstration
Symbol
Turn OFF
Use Button to
Demonstrate
Contactor Operation
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45. Main Contactor Identification
Line (High) Side
Load (Low) Side
Coil
Armature
Control Power taps
Coil Wires
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46. The Overloads
– They are often referred to as “Heaters”
– They are designed to heat up if current loads get too high
– Their purpose is to trip (open) under overload conditions
• Overload conditions are conditions where the circuit generates excess heat
– When they trip, they break the control power connection
• When control power is lost, the main contactor coil de-energizes, forcing the
main contactor to open
– They are adjustable
• They should only be adjusted by qualified electricians
– They are reset by pushing a button (usually red) on the
overload assembly
– There is an extension button attached to the enclosure door
to allow reset without opening the enclosure
• The overloads are connected to the load side of the contactor
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47. Overload Identification
Load (Low) Side Wires
Overloads
Reset Button
Line (High) Side, Connected to Contactor Load Side
Symbol
Click here to learn the
difference between an overload
and a breaker
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48. The Difference Between a Breaker
and an Overload
– When a gap occurs in a circuit path, an arc forms
– With lower currents and voltages, this arc is not noticeable, but
you may have seen it when turning a wall switch off at night
– At higher currents and voltages it is very noticeable, and can
damage equipment
• A breaker literally breaks the arc created when a switch opens up
(creating a gap) while the circuit is under a load
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49. Arc Generation
• In the original version of the movie “Frankenstein”, one of
the props was called a “Spark Gap” or “Jacob’s Ladder”
• The arc is created because the voltage is high enough to
jump the gap
– It literally strips electrons out of the air to create a virtual wire
– The arc is extremely hot, so it heats the air around it, causing it
to rise until the gap is too wide
– The wide gap causes the arc to cool until it can no longer strip
the electrons
– This “breaks” the arc and the process starts again at the bottom
Where does the arc come from, and how does a breaker
break it?
•
Exit

50. Arc Generation: Jacobs Ladder Part 1Exit

51. Arc Generation: Jacobs Ladder Part 2Exit

52. Arc Generation: Jacobs Ladder Part 3Exit

53. What a Breaker Does
– When the breaker is closed this has no effect
– When the breaker trips, the creates such a long path that the arc breaks
before it can cause damage
•
An arc tends to follow a surface, so a breaker is
designed with long internal surfaces
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54. How a Breaker Works
– When the latches release, the breaker springs open to an intermediate
(tripped) position
– Since the circuit is under load (or there would be no current), an arc
forms, but gets broken by the long arc path built into the breaker
– The breaker must be opened completely to reset the tripped condition
• The breaker contains spring loaded latches that release if current
rises above the designed value
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55. Overload Conditions
– Short cycling (discussed in part 1)
– Frozen driven equipment
– Sometimes, certain faults in the wiring
• They all have the same effect: they overheat the wiring
Overload conditions can be caused by several things:•
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56. How an Overload Works
– These elements are often called heaters
– Their purpose is to heat up faster than the wires, causing the overload to
trip long before the heat damages the wires
– The overload will also interrupt power to the control circuits, causing the
main contactor to open
An overload contains elements that have a higher resistance
than wires, so they will heat up faster under an overload
condition
•
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57. Load Stabs
– This facilitates ease in removing the can
– The leads don’t have to be disconnected to remove the can
– They are frequently labeled “T1”, “T2”, and “T3”
– They are referred to as “Load Stabs” because they connect
power to the load
– Other stabs are referred to as Line or Control stabs
– As discussed previously, the line stabs connect the buss to
the line side of the breaker
– The control stabs, which will be discussed later, connect the
control wiring to the field devices
The power wiring to the load (in this case a motor) goes
through a set of output stabs
•
Exit

58. Load Stab Identification
Front View Side View
Where They Connect To With Starter Installed
Symbol
Power Wires to
Motor
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59. Putting It Together Part 2
Breaker Contactor
Overload
Load Stabs
Not Visible (Behind Bucket): Line Stabs
Power Flow
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60. Part 2 Quiz Q1
• Name the major parts of the motor starter
power circuit
– The enclosure
– The breaker
– The contactor
– The overloads
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61. Part 2 Quiz Q2
• What allows for the bucket to be removed
without having to de-terminate wires
– Stabs
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62. Part 2 Quiz Q3
• What is the function of the breaker?
– To open the circuit if there is excess current flow
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63. Part 2 Quiz Q4
• What is the function of the contactor?
– To control starting and stopping of the motor
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64. Part 2 Quiz Q5
• What is the function of the overload?
– To trip the power if the circuit overheats
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65. Part 2 Quiz Q6
• Describe the order of the components in which
power is transferred from the buss to the motor
– Buss
– Power Stab
– Breaker
– Contactor
– Overload
– Load Stab
– Motor
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66. Part 2 Quiz Q7
• What is meant by the referring to the “High
Side”?
– The input side of a device
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67. Part 2 Quiz Q8
• What state is a device in when it is open?
– Off or de-energized
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68. Part 3: Control Wiring
• To Identify parts of the control wiring circuits
• To explain the function of each part
• To explain how the parts are connected
In This Section, You Will Learn :
Exit

69. The Control Transformer
– This voltage is frequently 5-120vac, and if supplied by an
external power supply, can be 24vdc (intrinsically safe), or
any other control voltage the design engineer selects.
– The line side of the transformer is usually connected to two
of the three line side main contactor leads.
– The transformer usually has 1 fuse installed in the load side
circuits.
– There may be more than 1 fuse, and they may also be
installed on the line side
– In this example, one side of the transformer is grounded to
the enclosure for safety
• The control transformer steps down the 480 VAC from
the power wiring to a more useful control voltage.
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70. Transformer Identification
Fuse
Transformer
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71. Basic Transformer Concepts
A transformer has many coils on one side (in this
case the line side), and fewer coils on the other. For
the purposes of this explanation, they are shown side
by side, but they are usually coiled one inside the
other, or around a metal core. There are many other
designs, but they all perform one basic function.
They change voltage from one potential to another.
They work by the principal of magnetic induction.
If you have a potential between H1 and H2, you will
get current flow. When this happens, a magnetic
field is formed in the “H” coils. The magnetic field
crosses into the “X” coils, and induces a current in
the “X” coil, but since the “X” coil has fewer
windings, it will have a lower voltage. Note that
there must be current flow for this to happen, and to
have current flow, you must have a voltage
difference between H1 and H2. If H1 and H2 are at
the same voltage there will be no current flow, no
matter how high that voltage is. This difference is
provided by tapping H1 into one phase of the
contactor line side, and tapping H2 into a different
phase.
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72. Terminology: Normally Open/Closed
• Discrete devices come in two types: Normally Open (NO), and Normally Closed (NC)
– NO and NC refer to the state the device is in when it is sitting in a box on the shelf
– An NO device will be open, or off. In other words, it will not conduct electricity
– An NC device will be closed, or on. It will conduct electricity
• When the device is activated (switched, pushed, or whatever), it will change to the
opposite state
– An NO device will close, and start conducting electricity
– An NC device will open, and stop conducting electricity
– In example, the main contactor discussed earlier is an NO device
• When speaking of a contactor, a relay, a switch, a pushbutton, or any
other control device, you must determine the state of the device first
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73. The Auxiliary Contactors
– Their purpose is to provide control circuit feedback as to whether
the main contactor (or overload) is open or closed .
– When the main contactor closes, or “changes state” normally
open (NO) contactors will close, and normally closed (NC)
contactors will open, or “change state” along with the main
contactor
– Auxiliary contactors can be “stacked” on top of each other
• This allows for more than just one or two contactors per
circuit
– They will be marked either with letters, or symbols to indicate
their normal state
The Auxiliary Contactors are located on the sides of the main
contactor (and the overload assembly)
•
Exit

74. Auxiliary Contactor Identification
Main Contactor
Aux Contactors
Exit

75. Auxiliary Contactor Demonstration:
Off
Turn ON
Use Buttons to
Demonstrate
Contactor Operation
Exit

76. Auxiliary Contactor Demonstration:
On
Turn OFF
Use Buttons to
Demonstrate
Contactor Operation
Exit

77. The Local/Off/Remote Switch
– Available modes in this application are:
• Hand: The motor will run unless the breaker or overload trips
• Off: The motor will not run
• Remote: The motor can be started and stopped at the remote
station. More complicated control circuits may have other
devices on this part of the circuit, such as switches relays,
pushbuttons, or PLCs
– Not all motor starters will have this switch.
– Many other control circuit designs are available, such as
Hand/Off/Auto (HOA)
The Local/Off/Remote switch selects the control mode•
Exit

78. Local/Off/Remote Switch
Identification
Switch
Exit

79. The Indicator Lights
– They are energized and de-energized by aux contactors
• These are NC for green, and NO for red
• The green lamp’s aux contactor is NC so that when the main
contactor is open, it will be closed, and the green lamp will be
energized, and vice versa
• The red lamp’s aux contactor is NO so that when the main
contactor is open, it will be open, and the red lamp will be de-
energized, and vice versa
– One of the lamps should be illuminated at all times.
– When neither light is illuminated, it indicates either a burnt out
lamp, a loss of power (control transformer fuse blown, overloads
open, or the breaker tripped), or a problem with the control
circuit.
• The indicator lights are red for Run, and green for Stop
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80. Indicator Light Identification
Indicator Lamps
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81. The Control Stabs
– They work the same way as the line or load stabs
– They are located above the load stabs in this example
• The control stabs are installed to ease removal and
installation of the bucket without having to disturb the
control wiring leading to the device
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82. Control Stab Identification
Side View
Where They Connect To With Starter Installed
Front View
Exit

83. The Field Devices
– For the purposes of this discussion, these consist of the remote
start/stop buttons.
• Some start stop stations can be much more elaborate, with
lead/lag capabilities, indicator lights, switches, relays, PLCs,
and even touchscreen controls.
• Not all motor controllers will have a remote station
The remote start/stop station is located near the device being
started
•
Exit

84. Example of a Complicated
Start Stop Circuit
This is an example that shows how
complicated the wiring can get. In this
example, there are two motors, with a
capability to start the motors locally, or if in
remote, to start them manually at any of
three Start/Stop stations, or let the motors
run in automatic with Lead/Lag capability.
There is also an alarm circuit.
Note that each motor starter has foreign
voltage from the other starter on their “B” aux
contactors, to allow the lag motor to monitor
the status of the lead motor contactor. This
means that there can be voltage from the
other starter present in the enclosure even
with the breaker open. This is why the only
way to be sure the entire enclosure is de-
energized is to pull the bucket.
Also note that with the exception of one
extra aux contactor and two control stabs,
the components in the enclosure are
identical to the starter being discussed in the
training. All the extra wiring is in the control
circuits external to the buckets.
Exit

85. Field Device Identification
Start Pushbutton
(NO)
Stop Pushbutton
(NC)
Exit

86. The Overload Aux Contactor
– It is an NC contactor
– It’s purpose is to interrupt power to the main contactor coil when the
overload trips
• This forces the main contactor to open, and stops power to the
control circuits as well as the load
• It will close again when the overload is reset
In this circuit, there is an aux contactor on the overload•
Exit

87. Overload Contactor IdentificationExit

88. Putting It Together Part 3
Aux
Contactors
Overload
Contactor
(behind
Reset
Button)
Wires to
Lamps and
Switch
Control
Transformer
Control
Transformer
Fuse
Power Taps to Control Transformer
High Side
Wires to Control
Stabs
Exit

89. Control Circuit Operation: Stopped
– There is load power up to the contactor, but no further
– The control transformer is energized, but aux contactors MA1 and
MA2 are NO, and the HOR switch is in off, so the only way control
power can flow is through MA3 to the green lamp
The first condition to consider is with the motor Stopped•
Exit

90. Control Circuit Operation: Hand
– In hand, power is sent directly to the main coil, which closes and
sends power to the load
– Aux contactors MA1 and MA2 and MA3 change state with the
main contactor, so the green lamp goes out, and the red lamp
illuminates
The next condition is with the motor in Hand•
Exit

91. Control Operation: Remote Stopped
– In remote stopped condition, the circuits are the same as when
the HOR switch is in off, with one exception
– Power is sent to the high side of MA1 and the start pushbutton,
but since they are open, this has no effect
The next condition is with the motor in Remote and Stopped•
Exit

92. Control Operation: Remote Run
– When the start pushbutton is pressed, it sends power to main coil
and it, MA1, MA2, and MA3 all change state
• When the start pushbutton is released, MA1 maintains power
to the main coil, and the motor continues to run until the stop
pushbutton is pressed to open the circuit, de-energize the
main contactor coil and open MA1, and return it to the
remote stop condition
In remote run condition, the circuits are the same as when
the HOR switch is in hand, with one exception
•
Exit

93. Control Operation: Overload
– When the overload changes state, so does it’s aux contactor
– When this aux contactor opens, it breaks power to all control
circuits, as well as de-energizing the main coil
• Neither light will be illuminated. This can be used to help
troubleshoot a malfunctioning starter
• The same symptoms will appear on either a tripped breaker, a
blown control fuse, or a burnt out lamp
In an overload (excess heat) condition, the overload will trip•
Exit

94. Part 3 Quiz Q1
• What is the purpose of the control
transformer?
– To step the 480 volts down to a more useful/safe
voltage for the control circuits
Exit

95. Part 3 Quiz Q2
• What is the purpose of an aux contactor?
– To provide feedback on main contactor state for
the control of other devices such as indicators
Exit

96. Part 3 Quiz Q3
• Where are aux contactors located?
– Attached to the sides of the main contactor
Exit

97. Part 3 Quiz Q4
• What controls the indicator lamps?
– Aux contactors
• What does a red lamp indicate?
– That the main power is energized (main contactor
is closed)
Exit

98. Part 3 Quiz Q5
• What is the purpose of the control stabs?
– To allow for the enclosure to be removed without
having to de-terminate the control device wiring
Exit

99. Part 3 Quiz Q6
• What is the purpose of the overload aux
contactor?
– To open the control circuit if an overload condition
trips the overloads
• How does it work?
– When the overloads trip, it opens the entire
control circuit
Exit

100. Part 3 Quiz Q7
• If the motor is in remote run, what position state
must the following components be in:
– The HOR switch
• Remote
– MA1
• Closed
– MA2
• Closed
– MA3
• Open
– Red Lamp
• On
– Green Lamp
• Off
Exit

101. Part 3 Quiz Q8
• Name four possible reasons for both lamps
being dark
– Breaker open
– Burnt out lamp
– Control fuse blown
– Overloads tripped
Exit