TL;DR
A breaker that won't close usually has a discharged spring or a coil fault. Check the spring charge indicator, test the closing coil voltage, and replace the coil or the breaker if the mechanism is damaged.
What you might see
- close command given but breaker does not close
- spring charge indicator shows discharged
- close coil energized but mechanism does not latch
- local close button does not operate breaker
Likely causes
Spring charging motor failed, leaving the closing spring discharged
Closing coil open circuit or incorrect control voltage reaching the coil
Anti-pump relay holding the close circuit open after a failed reclose attempt
Mechanical latch damaged or breaker racked into an intermediate (test) position
Required tools
- Multimeter (for control voltage and coil resistance)
- Insulated probes (category rated)
- Replacement closing coil or spring motor (if needed)
- Arc-flash PPE
- LOTO kit
Safety first
- Breaker control circuits inside an MCC contain live voltages (120V AC or 125V DC typical) even when the main breaker is open. Treat all control terminals as energized.
- Never rack a breaker to SERVICE position without first verifying operation in TEST. Racking an untested breaker into service can cause an arc-flash event.
Procedure
- 1
Check the spring charge indicator on the breaker face. A discharged indicator means the closing spring has not been charged by the motor.[1]
- 2
Listen for the spring-charging motor running after the previous open operation. No motor sound after a trip means the motor or its control circuit has failed.
- 3
With the breaker racked to the TEST position and the section dead-front in place, measure the control voltage at the closing coil terminals using a multimeter.
Warning: Control voltage is present even in the TEST position. Use insulated probes and category-rated equipment. - 4
If control voltage is present but the coil does not operate, measure the coil resistance. An open circuit (infinite resistance) means the coil is burned out and needs replacement.[1]
- 5
If no control voltage at the coil, trace the close circuit: check the anti-pump relay, the key switch, and the close pushbutton for continuity.
- 6
If the spring-charging motor has failed, de-energize the breaker control circuit, replace the motor, and verify the spring charges correctly.[1]
- 7
After repairs, rack the breaker to TEST position and send a close command. Confirm the breaker closes and the spring re-charges for the next operation.
- 8
Rack back to SERVICE position only after the breaker has proven functional in TEST.
Sources
Square D Model 6 Motor Control Center Instruction Bulletin, Square D (Schneider Electric)
Square D Model 6 MCC installation and maintenance instructions, circuit breaker closing mechanism and coil replacement procedures (general)
View source
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