MCCB Primary Injection Testing
MCCB Primary Injection Testing
(OP)
For circuit breakers in the 600-1200A frame size, does anyone know a published example of a failure rate for breakers showing up on site?
I know that manufacturers perform a small sample of circuit breaker trip unit tests, but I'm curious if anyone has anecdotal or even better published failure rates after they leave the factory and prior to energizing on site?
Try to place a conceptual price on primary injection testing of MCCB's on site prior to energizing in a critical facility.
The client is being convinced by an on site electrician tat the primary injection testing is a waste, and I think it is worth it. BTW, I think the electrical contractor didn't carry any money for the testing which is carefully detailed in the contract. :(
I know that manufacturers perform a small sample of circuit breaker trip unit tests, but I'm curious if anyone has anecdotal or even better published failure rates after they leave the factory and prior to energizing on site?
Try to place a conceptual price on primary injection testing of MCCB's on site prior to energizing in a critical facility.
The client is being convinced by an on site electrician tat the primary injection testing is a waste, and I think it is worth it. BTW, I think the electrical contractor didn't carry any money for the testing which is carefully detailed in the contract. :(





RE: MCCB Primary Injection Testing
For 600 A and above, the current test seems like a good idea to me. We have had clients who test EVERY MCCB, down to 15A.
RE: MCCB Primary Injection Testing
I did contract work for a client who tested every three-pole 480-volt MCCB and MCP. This was a large refinery and during the course of maintenance on a production unit these sometimes numbered over a hundred units. It was common to find as many as 10% failures based on direct current injection tests.
old field guy
RE: MCCB Primary Injection Testing
RE: MCCB Primary Injection Testing
Failure to mechanicaly open or close?
Failure to trip at all?
Failure to trip within mfg spec?
Failure to trip within NEMA spec?
Contact resistance out of (what)spec?
What else?
Thank you in advance.
RE: MCCB Primary Injection Testing
Any of these will do.
"Failure to open or close" on manual operation means that the device cannot be depended on to provide the isolation and control as designed.
"Failure to trip" means that the device can't provide the selectivity for coordination with other devices, meaning a branch circuit fault brings down much more equipment than intended, or much more energy is released into a fault causing more damage and safety issues.
"Contact resistance out of spec." means heat buildup and eventual (and often catastrophic) failures.
old field guy
RE: MCCB Primary Injection Testing
Based on these numbers, MTBF = 1/0.0096 = 104 years; MTTR = 9.6 hours; availability = 100*(1-(9.6/104yr*365*24))=99.9989%
I don't see any info in the Gold Book on defect rates on new breakers. Anecdotally, I've generally heard numbers more in the 2-5% range on new breaker failure rates, and I've seen trip units delivered with an 80% failure rate, they just would not trip at all at any current level (which really sucks when the replacements need to be shipped to the US from Europe).
Hope this helps.
RE: MCCB Primary Injection Testing
Makes me wonder how many of these were put in service and never tested. Pretty scary.
RE: MCCB Primary Injection Testing
RE: MCCB Primary Injection Testing
Field testing should be done according to NETA standards and not to manufacture's - especally with thermal mag units. Too hard to create a bench enviroment same as they use.
We require all of our new MCCB to be tested by supplier before they are put into service. :)
RE: MCCB Primary Injection Testing
Dont trust a supplier that they tested it, they all say they do, ask for a detailed test report that meets or exceeds NETA specs. (Our specs greatly exceed NETA's for every breaker that ships)