ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
New tool
by gfretwell - 10/24/20 11:09 AM
Where is Everyone?
by Bill Addiss - 10/17/20 07:04 PM
Beyond Belief
by gfretwell - 09/27/20 12:03 AM
New in the Gallery:
Facebook follies, bad wiring
FPE in Germany pt.2
Who's Online Now
0 registered members (), 15 guests, and 18 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Using a sub feed lug #89971 10/26/04 09:48 AM
Joined: Sep 2004
Posts: 86
N
Norstarr Offline OP
Member
Have a 100 amp main breaker panel in a residence. Have to add a sub panel and plan to feed it with #4's and use a sub feed lug instead of a breaker. The sub panel is then protected by the 100 amp main breaker. Any code violation here?
Ron

2017 / 2014 NEC & Related Books and Study Guides
Re: Using a sub feed lug #89972 10/26/04 10:30 AM
Joined: Sep 2003
Posts: 649
W
winnie Offline
Member
I would double check the stab ratings on the main panel that is feeding the sub. Some panels limit the maximum current ratings of loads connected to a single bus stab.

Also the use of #4s falls right onto an ugly bit of NEC 310.15(B)(6). #4Cu is permitted to be protected with a 100A OCPD when it is used to supply the _main_ power feed of a single residence. #4Cu does not have sufficient ampacity to be protected at 100A _in general_, but for the specific load described in 310.15(B)(6) it is permitted to do so. This means that #4Cu is _not_ sufficient for the feed to a 100A subpanel.

But there is yet another exception, which is that the feed to any subpanel in a residence is not required to be larger than the main feed. So I think that using the #4Cu as you describe will be okay until such time as the main service is upgraded, at which point you will need to protect the subpanel at less than 100A.

-Jon


Featured:

2020 National Electrical Code
2020 National Electrical
Code (NEC)

* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
Posts: 165
Joined: March 2007
Show All Member Profiles 
Top Posters(30 Days)
BigB 3
Popular Topics(Views)
270,787 Are you busy
205,000 Re: Forum
193,115 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3