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#75226 - 02/17/07 04:44 PM Protection for wire derated.
Cinner Offline

Registered: 12/01/04
Posts: 77
Loc: Kelowna, B.C., Canada
If you are derating wire due to conduit fill(example - 4/0 derated to 3/0 ampacity) should the circuit breaker be sized to protect the new derated amapacity of the 4/0?

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#75227 - 02/17/07 05:09 PM Re: Protection for wire derated.
RobbieD Offline

Registered: 02/23/03
Posts: 238
Loc: Canada
No, stay with circuit breaker size and just increase the awg of the wire when you have to derate.

[This message has been edited by RobbieD (edited 02-17-2007).]

#75228 - 02/17/07 05:13 PM Re: Protection for wire derated.
SteveFehr Offline

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
The derated ampacity cannot exceed the overcurrent protection. So, you either have to downsize the breaker or upsize the cable. Normally, it's the latter since the original breaker size is chosen for a reason, but using a smaller breaker is OK if circumstances allow.

#75229 - 02/19/07 05:48 AM Re: Protection for wire derated.
ghost307 Offline

Registered: 05/09/05
Posts: 881
Loc: Chicago Illinois USA
Are you saying that I can't feed a 15 amp load with a 20 amp breaker using #8 wire???
...or did I read your post wrong?


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