ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
IRC M1307.3
by gfretwell. 08/20/18 11:16 PM
Upgrade the old panel
by HotLine1. 08/20/18 07:00 PM
Light Pole Grounding
by HotLine1. 08/20/18 05:34 PM
Calling all Non-US members!! (Non-US only)
by Bill Addiss. 08/13/18 05:52 PM
depth of duckbank
by ghost307. 08/12/18 09:26 PM
New in the Gallery:
Plug terminals
Housebilding DIY wiring
Who's Online Now
0 registered members (), 5 guests, and 23 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
NM-B Wire #81290
08/01/02 10:36 PM
08/01/02 10:36 PM
C
Curtis Wilson  Offline OP
Junior Member
Joined: Jul 2002
Posts: 2
Portland Oregon
Question?
Article 336.26 states that type "NM" cable must be amperage rated using the 60c column on table 310.16
Article 336-30.(b) states that NM cable having the "-B" extension have their conductors insulation rated at 90c.
If I have a 200 amp main panel feeding a subpanel and both terminal ratings (on the breaker and lugs on the subpanel)are rated @ 75c, can I use 6-3 NM-B romex as the subfeeder conductors using a 70 amp breaker in the main panel?
Thanx..
Curtis

2017 / 2014 NEC & Related Books and Study Guides
Re: NM-B Wire #81291
08/01/02 11:13 PM
08/01/02 11:13 PM
C
caselec  Offline
Member
Joined: Apr 2002
Posts: 558
San Jose, CA
You may use the 90C column for applying correction factors but the maximum ampacity of NM-B cable after any correction factors are applied can not exceed what is listed in the 60C column. 6-3 is good for 55 amps max.

Curt


Curt Swartz
Re: NM-B Wire #81292
08/02/02 09:58 AM
08/02/02 09:58 AM
3
3 Way  Offline
Junior Member
Joined: Jul 2002
Posts: 6
TX
You might consider 110.14(C)(1)(a)...(2),(3) covering equipment terminations generally.

(a) Termination provisions for circuits rated <100 amps...
(2)Conductors w/ higher temp ratings are allowed, provided the ampacity of such conductors is based on 60C
(3)Conductors of higher temp are allowed if the equipment is listed for use with such conductors

Provision (3) suggests 75C may be possible since the equipment lugs are rated 75C, however...

I would defer to NEC 2002 334.80 which specifically restricts NM to 60C. Section 334.112 requires NM cables be constructed w/ 90C insulation.

With all that, I see it like "caselec". 90C sets the starting ampacity for derating purposes, but in no case shall the conductor be operated above it's 60C limit.

3way


Featured:

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

 

Member Spotlight
Tom
Tom
Shinnston, WV USA
Posts: 1,044
Joined: January 2001
Show All Member Profiles 
Top Posters(30 Days)
BigB 3
Popular Topics(Views)
248,669 Are you busy
186,403 Re: Forum
175,893 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.016s Queries: 14 (0.005s) Memory: 0.9510 MB (Peak: 1.0771 MB) Zlib enabled. Server Time: 2018-08-21 07:57:10 UTC