Use a test kit or secondary injection for checking the trip unit. My preference is to push primary current to verify that the CT's or other current sensor is working and to measure voltage drop at rated current to check for loose connections.
Trip unit's operated correctly but the trip pin never hit the trip bar hard enough to trip the breaker.
At one aerospace facility we failed 90% of the 400-2000 amp breakers during a holiday shutdown. We seemed to find more problems with them. Draw out circuit breakers were easier to test. We didn't find that many problems except loose joints which a good thermal scan would pick up. Pushing 6ka for the 20 minutes on each phase was a pain. With good bus bars from the set to the breaker we could test 2,000A breakers in place. When I was in the breaker testing business we had 10 kA, 20ka, and 50 kA "portable" test sets. RE: Primary injection testing on 800 amp breakers? rcw retired EE (Electrical) 31 Jul 20 08:32 It seems that we would want to know if these devices were actually functional. It's common to see 3000 A and 4000 A MCCBs. They weren't willing to spend any many to put in low voltage switchgear or they just didn't know any better. When arc flash is figured in, the reliability of MCCBs is much more important (at 480 and 600 V).Īlso, I've been in many manufacturing facilities where MCCBs were used for everything. Before we worried about arc flash, if a MCCB failed to open, generally something upstream would eventually trip and that was seen as not a big deal. The arc flash calculations are based on that breaker tripping per the manufacturer's published time-current curve regardless of age. The majority of arcing faults will occur downstream of a molded case breaker. But the testing recommendations are all over the place and don't really take into account the impact of arc flash incident energy levels. I agree exercising the breakers is important and "routine" injection testing is probably never practical except for larger breakers. They experience about a 2% failure rate on brand new breakers. I know of one major semiconductor company that does primary injection testing on every new molded case breaker - in the thermal range, IIRC.
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