Breaker Rating

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Lightninarrester

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Guys,

Where in the NEC Code does it require to derate the breaker size to 80% if used in an enclosure (i.e. lighting panel)? Is there such a requirement? Thanks

[ September 21, 2005, 11:25 AM: Message edited by: Lightninarrester ]
 
Re: Breaker Rating

You don't "derate" the breaker to 80%. Rather, you limit the calculated load to 80% of the breaker's rating. Or more precisely, you select a breaker that has a rating at least "the non-continuous load plus 125 percent of the coninuous load." Reference 210.20(A). Lighting is considered a "continuous load."
 
Re: Breaker Rating

Thanks, so the requirement comes from the calculated continuous load plus 125%. I thought there was a requirement about using only up to 80% of the breaker rating if it is enclosed.

[ September 21, 2005, 12:30 PM: Message edited by: Lightninarrester ]
 
Re: Breaker Rating

most breakers are tested for a use of 80% of it stamped rating. Once you get around the 400 or 500 amp range you can find breakers that are 100% rated for continous use.
 
Re: Breaker Rating

All breakers are rated for use at 100% non-continuously.

The continuous load on most breakers can not exceed 80%. :)
 
Re: Breaker Rating

There are larger 100% rated breakers available in 600a and larger frames though. For most electricians 100% breakers are not an issue because they are not available in the lower rating as most of us may be accustomed to. The 100% rated breaker must be installed in an enclosure listed for the application and 90degC rated cable used but applied at 75degC. Cable is sized based upon 100%+100% and not 125%+100% which may allow the next size smaller cable to be used. And, if the wind is blowing in the right direction and the cards are in your favor there is a very long shot that you may be able to drop down a frame size. But there you would have to be very lucky.
Smaller cable and possibly a smaller breaker is intended to save money.
 
Re: Breaker Rating

Originally posted by charlie b:
Lighting is considered a "continuous load."
Click to expand...
IMO that is a bit of an overstatement.

It may be a continuous load or it may not, the NEC leaves that up to the designer / installer. :)
 
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