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Protection for wire derated. #75226 02/17/07 07:44 PM
Joined: Dec 2004
Posts: 78
C
Cinner Offline OP
Member
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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Re: Protection for wire derated. #75227 02/17/07 08:09 PM
Joined: Feb 2003
Posts: 231
R
RobbieD Offline
Member
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).]

Re: Protection for wire derated. #75228 02/17/07 08:13 PM
Joined: Mar 2005
Posts: 1,213
S
SteveFehr Offline
Member
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.

Re: Protection for wire derated. #75229 02/19/07 08:48 AM
Joined: May 2005
Posts: 984
G
ghost307 Offline
Member
Huh?
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?


Ghost307

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