Transcript E2 Subject1
E2 Motors and Motor Starting
#3 Contactors and Motor Starters
Descriptions of Contactors
• Contactors have the following:
– Coil (electro-magnet)
– Contacts (switch)
– Mechanical linkage (armature)
• Contactor sequence of operation:
– Coil is energized
– Armature pulls in
– Contacts close
– Power flows through contacts to the load
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Symbols for Contactors
Symbols are shown “de-energized” (no power)
with contacts “normally open”
Coil
Contact
Single
pole
115v
Double
pole
208-230v, 1
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
Triple
pole
208-230v, 3
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Visualizing symbols with power on
• The following slide illustrates what
happens when the power is turned on
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Contactor coil “energized”
Contacts close
Coil
Contact
Single
pole
115v
Double
pole
208-230v, 1
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Triple
pole
208-230v, 3
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Contactor in Motion
• The following slide is a front view of a
contactor
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Contactor Operation
Power to
Contactor
LINE
L1
L2
Contacts
pull in
CONTROL
CIRCUIT
Control Circuit
energized
T1
T2
Power to
Load
LOAD
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Contactor Cut-away view
• The side view of a contactor shows how
the coil pulls in the armature and closes
the contacts
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Side View
LINE
L1
L2
T1
T2
CONTROL
CIRCUIT
LOAD
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Side View
LINE
L1
Power to
L2 Contactor
CONTROL
CIRCUIT
Magnetic Coil
energized
Contacts
pulled in
T1
Power to
T2 Load
LOAD
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Contactor Troubleshooting
• 1st Test: Check the mechanical linkage
– Armature must move freely
– Burned coils can restrict movement
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Check Coil Linkage
LINE
L1
Safety tip:
Always use
wooden dowel
L2
CONTROL
CIRCUIT
Close
Contacts
T1
Power to
T2 Load
LOAD
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Contactor Troubleshooting
• 2nd Test: Ohm the contactor coil
– 0 ohms means it’s shorted
– Infinite ohms (OL) means coil is open
– Measurable resistance, coil is good
• Note: If the coil is shorted or open, correct
the problem before replacing contactor
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Checking the Contactor Coil
LINE
L1
L2
CONTROL
CIRCUIT
Remove
wires
from coil
OHM Coil
Measurable
resistance
is GOOD
123Ω
00LΩ
T1
T2
0Ω = Shorted
Infinite Ω = Open
LOAD
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Contactor Troubleshooting
• 3rd Test: Check voltage across contacts
(voltage must be applied):
– 0 volts means contacts are good
– Line voltage means contacts are open
– Any voltage reading means contacts are
burned
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Check Voltage Across Contacts
LINE
L1
CONTROL
CIRCUIT
Example:
230 Volt Line
L2 10 Volts across contacts
Replace
Contactor
NOTE: Any
voltage reading
across contacts
can mean
contacts are BAD.
0
10
T1
Zero is
good
T2
LOAD
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Motor Starter
• Basically a contactor with overloads
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Motor Starter Diagram
Coil and contacts:
Magnetic overloads:
Overloads open switches
on high current draw
Switches are wired in series
Any switch that opens will
interrupt power to the coil
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Motor Starter
Power In
Coil
Contacts
(inside)
Overloads
Manual
Reset
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Power Out
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© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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