MCC Bus Temperature based on 105C

[JensenDrive]

I noticed recently that Eaton sent in some submittals for 480V MCCs with bus where they say ampacity is based on 105C max operating temperature in a 40C ambient. Then they connect circuit breakers directly to the bus, and the circuit breakers have terminal temperatures limited to 75C. The also install CTs around the bus with a thermal rating factor of 1.0 at 30C. I find the highest temp you can get a CT rated for is 55C. I challenged the matter, and Eaton only stated that this was OK per UL standard 845. I have found that Eaton uses this same 105C bus rating in 480V switchgear and panelboards. Do all MCC/electrical panel mfrs use this same high bus temp with equipment rated much less than 105C? Does this concern anyone?

 

[jraef]

Then they connect circuit breakers directly to the bus, and the circuit breakers have terminal temperatures limited to 75C.

Nope. Circuit breakers have WIRE TERMINALS rated for 75C, but they are not connecting them directly to the bus using terminals. They are bolted directly to bus bars. It's the same in Switchboards.


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