ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
Calling all Non-US members!! (Non-US only)
by HotLine1. 06/13/18 01:50 PM
GE Lighting Recalls LED Tube Lamps
by Admin. 06/12/18 09:32 PM
Ketra Recalls Recessed Downlights
by Admin. 06/12/18 09:17 PM
diazed fuses
by Texas_Ranger. 06/11/18 07:31 AM
soda can fuse from UK, facebook
by wa2ise. 06/06/18 11:02 PM
New in the Gallery:
Plug terminals
Housebilding DIY wiring
Who's Online Now
0 registered members (), 7 guests, and 8 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Circuit Design #167751
08/19/07 03:26 PM
08/19/07 03:26 PM
W
windmiller  Offline OP
Junior Member
Joined: Dec 2006
Posts: 43
Alaska
Whats the rule on feeding a 300A Fused Disconect from a 400A breaker?

thanks

Windmiller


We all live under one King
2017 / 2014 NEC & Related Books and Study Guides
Re: Circuit Design [Re: windmiller] #167759
08/19/07 08:05 PM
08/19/07 08:05 PM
HotLine1  Offline

Member
Joined: Apr 2002
Posts: 6,973
Brick, NJ USA
More info required for answer.


John
Re: Circuit Design [Re: HotLine1] #167768
08/19/07 10:39 PM
08/19/07 10:39 PM
W
windmiller  Offline OP
Junior Member
Joined: Dec 2006
Posts: 43
Alaska
Hi,
This is from a 480 V MCC to a maint. shop.

This is a feeder to supply power to the building.

No 300A plug in bucket is available and no other place to get power except from 480V MCC with a new section and a frame mounted 400 CB.

The feeder is 3/C 500 MC.

Thanks,

Windmiller


We all live under one King
Re: Circuit Design [Re: windmiller] #167770
08/19/07 10:56 PM
08/19/07 10:56 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,227
Estero,Fl,usa
500 MCM is 380a @ 75c
I don't see a real problem. If you can get in under the feeder tap rules it is a slam dunk and you can probably use 240.4(B) if it comes down to it.

From a practical sense, you are really only providing short circuit protection in the 400a breaker since overload protection will come with the 300a. That is how they rationalize the "tap rules".

Last edited by gfretwell; 08/19/07 10:57 PM.

Greg Fretwell
Re: Circuit Design [Re: windmiller] #167907
08/22/07 02:36 PM
08/22/07 02:36 PM
electure  Offline

Member
Joined: Dec 2000
Posts: 4,268
Fullerton, CA USA
Quote
This is a feeder to supply power to the building.


If so, it may qualify for an outside the building tap of unlimited length per 240.21(B)(5)


Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
electure
electure
Fullerton, CA USA
Posts: 4,268
Joined: December 2000
Show All Member Profiles 
Top Posters(30 Days)
twh 5
Popular Topics(Views)
247,623 Are you busy
184,967 Re: Forum
174,205 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.036s Queries: 15 (0.015s) Memory: 0.9681 MB (Peak: 1.1094 MB) Zlib enabled. Server Time: 2018-06-21 04:40:59 UTC