MCB miniature circuit breaker 480 delta

[jfw1]

I am working on electrical design of a machine panel supplied by customer 480V delta. They are asking for circuit breakers for the motor connections and while stumbling around learning the difference between UL489 and UL1077, I also noticed MCB (miniature circuit breakers) do not list ratings for 480 delta only 480 wye. I am curious to know the technical reasoning behind this? As it looks now, I am going to request deviation to use fuses for the 3/4 hp motor protection. The customer previously used a 480 wye MCB for the 480 volt delta connection, I understand this to be a common mistake and should not be done. Can someone offer some details to the MCB and if the 480 delta is okay?

 

[davidbeach]

With only a wye rating, they are only rated for 277V to ground and therefore they only need to interrupt 277V per pole. In a delta application they could be forced to interrupt 480V on one or more poles and may not succeed in doing so.

 

[dpc]

Take a look at discussion of "slant" ratings in here:

http://www.ul.com/global/documents/...l/newsletters/MoldedCaseCircuitBreakersMG.pdf

David Castor

http://www.cvoes.com

 

[jfw1]

Does anyone know of a manufacturer that sells a 480 Delta rated Miniature Circuit Breaker?

 

[jraef]

You are right, it's a very common problem. But why change to fuses? There are UL489 MCCBs rated for 480V delta that are not much bigger than what the 480 "slash rated" MCBs would have been. About +1" in H and W, roughly the same depth for DIN rail versions.






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