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

Re: Protection for wire derated. #75228
02/17/07 09:13 PM
02/17/07 09:13 PM
S
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,213
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.

Re: Protection for wire derated. #75229
02/19/07 09:48 AM
02/19/07 09:48 AM
G
ghost307  Offline
Member
Joined: May 2005
Posts: 943
Chicago Illinois USA
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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