MCC Rating
MCC Rating
(OP)
Our MCC's have a symmetrical fault current rating. I was wondering if that was 1/2 cycle or 3-5 cycle fault current rating? Also, for what applications would one use the 1/2 cycle vs the 3.5 cycle fault levels (eg. which one for relay coordination)?
Thanks.
Thanks.






RE: MCC Rating
For relay coordination it depends. Some equipment such as fuses and molded case breakers can interrupt fault currents during the first cycle, while other equipment such as high-voltage breakers 1.5 to 8 cycles can take to open. This is typical for instantaneous settings. For time delayed settings the fault current will decay and you'll probably need the current after 0.3-0.5 seconds or after whatever time-delay you want.
See also:
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RE: MCC Rating
Also, if coordinating protection in a MCC and say a high-voltage breaker on the other side of the transformer, which fault level would I use in the TCC (1/2 cycle or contact parting .. 3-5 cycles).
Thanks.
RE: MCC Rating
Yes, your MCC must be able to handle this max. fault-current. (if there is a fault)
Also, if coordinating protection in a MCC and say a high-voltage breaker on the other side of the transformer, which fault level would I use in the TCC (1/2 cycle or contact parting .. 3-5 cycles).
What protective elements do you use? (O/C Relays, instantaneous relays, fuses, etc.?) Dou you have to coordinate with downstream devices?