ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

ECN Shout Chat
Top Posters(30 Days)
Admin 16
Recent Posts
ESA Arc flash course
by TheShockDoctors. 03/24/17 10:15 AM
fuse rejectors
by HotLine1. 03/24/17 07:53 AM
Another Forum Update
by Admin. 03/22/17 03:04 PM
Dining room plugs
by watersparkfalls. 03/21/17 10:31 PM
TRUE POWER
by jraef. 03/21/17 09:13 PM
New in the Gallery:
SE cable question
Popular Topics(Views)
231,416 Are you busy
166,135 Re: Forum
160,592 Need opinion
Who's Online Now
0 registered members (), 48 guests, and 13 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#75226 - 02/17/07 08:44 PM Protection for wire derated.  
Cinner  Offline
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?


Work Gear for Electricians and the Trades

#75227 - 02/17/07 09:09 PM Re: Protection for wire derated.  
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).]


#75228 - 02/17/07 09:13 PM Re: Protection for wire derated.  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,198
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 09:48 AM Re: Protection for wire derated.  
ghost307  Offline
Member
Joined: May 2005
Posts: 900
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


Member Spotlight
NickD
NickD
Amish Country, PA
Posts: 46
Joined: March 2013
Show All Member Profiles 
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.010s Queries: 14 (0.003s) Memory: 0.7566 MB (Peak: 0.8854 MB) Zlib enabled. Server Time: 2017-03-25 11:44:29 UTC