Breaker ratings in Switchgear

[MD88]

Hello,

Just a quick question... I'm aware of the 80% derating of breakers, when they are in an enclosure... does this apply to larger relay-controlled power circuit breakers as well? For example, would a 4000A, 4.16kV breaker be rated to carry 3200A continuously?

Thanks!

 

[MD88]

Here's the specific question...

I have a 3000kVA 4160/480V transformer feeder a 480V switchgear lineup.

Now, 3000kVA = 3000/480/1.73 = 3612A

If I want to be able to use the full 3000kVA, is a 4000A main breaker on the switchgear good enough? Or must I bump it to 3612*1.25 = 4515A ?

Thanks!

 

[jim dungar]

"Power breakers" (i.e. ANSI style) are usually 100% rated.

 

[SG-1]

I cannot speak for other manufacturers, but our ANSI breakers carry a continous rating as shown on the nameplate.

http://www.google.com/search?hl=en&...rfai=CnoYPt_o8TL7YLoqINoWGvaoNAAAAqgQFT9DPPtM

Open the PDF for Extra Capacity Breakers on the left.
You will see the current ratings on page 2.

 

[zog]

Yep, 100% rated, switchgear guys do it so it makes sense