1. E2 Motors and Motor Starting
#3 Contactors and Motor Starters

2. 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

3. Symbols for Contactors
Symbols are shown “de-energized” (no power) with contacts “normally open”
Coil
Contact
Single pole
Double pole
Triple pole
115v
v, 1
v, 3
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

4. 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

5. Contactor coil “energized”
Contacts close
Coil
Contact
Single pole
Double pole
Triple pole
115v
v, 1
v, 3
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

6. 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

7. Control Circuit energized
Contactor Operation
Power to Contactor
LINE L1 L2
Contacts pull in
CONTROL CIRCUIT
Control Circuit energized
Power to Load T1 T2
LOAD
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

8. Contactor Cut-away view
The side view of a contactor shows how the coil pulls in the armature and closes the contacts
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

9. Side View LINE LOAD L1 L2 T1 T2 CONTROL CIRCUIT
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

10. Magnetic Coil energized
Side View
LINE
Power to Contactor L1 L2
CONTROL CIRCUIT
Magnetic Coil energized
Contacts pulled in
Power to Load T1 T2
LOAD
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

11. 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

12. Check Coil Linkage LINE LOAD Safety tip: Always use wooden dowel
CONTROL CIRCUIT
Close Contacts
Power to Load T1 T2
LOAD
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

13. 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

14. Checking the Contactor Coil
LINE L1 L2
Measurableresistance is GOOD
CONTROL CIRCUIT
Remove wires from coil
OHM Coil 0L
0 Ω
123Ω
0Ω = Shorted
Infinite Ω = Open T1 T2
LOAD
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

15. 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

16. Check Voltage Across Contacts
LINE
Example:
230 Volt Line
10 Volts across contacts L1 L2
Replace Contactor
CONTROL CIRCUIT
NOTE: Any voltage reading across contacts can mean contacts are BAD. 10
Zero is good T1 T2
LOAD
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

17. Motor Starter Basically a contactor with overloads
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

18. 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

19. Motor Starter Power In Coil Contacts (inside) Overloads Manual Reset
Power Out
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2

20. END OF Contactors and Motor Starters
© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2