Molded Case Circuit Breaker PM strategies
Molded Case Circuit Breaker PM strategies
(OP)
Good morning,
Please share with me your current practices/strategies on Molded Case Cicuit Breaker ownership.
What do you do for PMs? Do you PM those MCCCB or run to failure?
what mitigation plan? (putting a fuse in line with the breaker, etc..)
MCCB are not draw out breakers, they are bolted on to the bus, and it is not likely to take the bus down for breaker PM.
How certain can you be that your breaker will trip when required?
No PM on your breaker send the incident energy levels in the 3 digits numbers, where your 100cal/cm^2 flash suit can't insure protection.
I need some opinions/ suggestions on that topic.
Thank you for sharing your knowledge.
CKH17(electrical)
Please share with me your current practices/strategies on Molded Case Cicuit Breaker ownership.
What do you do for PMs? Do you PM those MCCCB or run to failure?
what mitigation plan? (putting a fuse in line with the breaker, etc..)
MCCB are not draw out breakers, they are bolted on to the bus, and it is not likely to take the bus down for breaker PM.
How certain can you be that your breaker will trip when required?
No PM on your breaker send the incident energy levels in the 3 digits numbers, where your 100cal/cm^2 flash suit can't insure protection.
I need some opinions/ suggestions on that topic.
Thank you for sharing your knowledge.
CKH17(electrical)






RE: Molded Case Circuit Breaker PM strategies
RE: Molded Case Circuit Breaker PM strategies
The manufacturers usually say to exercise it twice a year, but there is applications where it is not really feasible due to the process downstream. There is also cases in the industry where the MCCB did not trip when it was required to, altough it was exercised. Also, do you think that current injection testing does more harm than good to the breaker?
RE: Molded Case Circuit Breaker PM strategies
I'm only a consultant, but I'm aware of a high-tech firm that does current-injection trip test of EVERY molded-case breaker at installation. The testing outfit told me that the infant mortality on small molded case breakers right out of the box has been about 2%. I'm not sure what they do for periodic maintenance testing.
There are plenty of cases where MCCBs fail to trip. I think exercising the breakers periodically is essential.
RE: Molded Case Circuit Breaker PM strategies
It's not my field, but:
PM of every MCCB!!!! twice a year!!!!
IR scan, yes- must, but current injection for every MCCB????
May be critical MCCB or group MCCB.
Regards.
Slava
RE: Molded Case Circuit Breaker PM strategies
RE: Molded Case Circuit Breaker PM strategies
This PM program was started by a MCB failure. A panelboard breaker failed to trip and the resulitng melt down and fire took down a Central Office in New York City around Wall Street. Big losses.
The MCB failure rate durign tests was less than 2-3%. Most problems were loose connections or, once in a while, a sticky trip unit. Cleaning the equipment and torquing the bus as we did the testing was probably more beneficial than the actual tests. Later, IR scans located most problems and the test program was stopped.
I would recommend an annual IR scan, tripping the breaker a couple of times with the handle.
RE: Molded Case Circuit Breaker PM strategies
NFPA 70B and NETA Maintenance Testing Standards recommend inspection and exercise every 12 to 24 months and injection trip/contact resistance every 3 to 5 years. Also any breaker that has interrupted a fault close to its interrupting rating should be inspected and tested before being returned to service.
RE: Molded Case Circuit Breaker PM strategies
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If we learn from our mistakes I'm getting a great education!
RE: Molded Case Circuit Breaker PM strategies