ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
Al Hildenbrand - Minneapolis - obituary
by bcpappas - 02/02/23 08:01 PM
Violation?
by renosteinke - 01/27/23 09:52 PM
Does NEC 551.71 (F) apply to dwellings?
by BigB - 01/20/23 10:46 AM
Power submeter connections
by HotLine1 - 01/19/23 09:09 AM
New in the Gallery:
Burger King crown sillyness
Burger King crown sillyness
by wa2ise, December 11
240/208 to a house
240/208 to a house
by wa2ise, October 9
Who's Online Now
1 members (mbhydro), 21 guests, and 11 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
#77646 07/06/01 02:08 AM
Joined: Jul 2001
Posts: 29
T
tmon Offline OP
Member
In Mike Holts "Masters Electrician Prep Book", he refers to the 90 degree column in T310-16 and states that this column is used primarily for ampacity derating. Has anyone else read or heard this?

Stay up to Code with the Latest NEC:


2020 NEC & Related Reference & Study Guides
2020 NEC & Related Reference & Study Guides
Pass Your Exam the FIRST TIME with these Exam Prep Combos:
 

>> Master Electrician Exam Prep     >> JourneyMan Electrician Exam Prep
 

Joined: Oct 2000
Posts: 5,392
S
Member
Hi tmon,
yes , we are allowed to use the highest figure to start derating calc's from, i believe there was a code cycle to clear this up, but am at a loss this morning for an article...

Joined: Jan 2001
Posts: 75
G
Member
It's always been that way.

Most earier Circuit Breakers ( small size ) were rated for 60º terminations.

Now many are rated for 60/75º terminations.

Usually only high voltage systems and bus work is the only items rated for 90º terminations.

Look at the labeling within panels and on equipment terminal info.

Also NEC 110-14(c) must be followed. Although is has only been in the NEC the last few cycles, it has always been in 110-3(b) and the UL White book has had the info for many mnay years, usually with-in the first 8 pages of text.

Glenn

Joined: Oct 2000
Posts: 5,392
S
Member
thanks Glenn
[Linked Image]

Joined: Oct 2000
Posts: 2,722
Broom Pusher and
Member
tmon,

Welcome to the group!!!

Just wanted to point out one of the more "simpler" points on using the 90 degree column for derating is the reason we can put upto 9 current carrying conductors [#12 THHN cu] in the same raceway, and still have them rated at 20 amp max.
What is being done here is the 30 amps maximum for #12 in the 90 degree column is used for the derating number - so for 9 current carrying conductors, 70% of 30 amps is 21 amps.

Scott SET.

Quote
Originally posted by tmon:
In Mike Holts "Masters Electrician Prep Book", he refers to the 90 degree column in T310-16 and states that this column is used primarily for ampacity derating. Has anyone else read or heard this?


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

Link Copied to Clipboard
Featured:

Tools for Electricians
Tools for Electricians
 

* * * * * * *
2023 National Electrical Code (NEC)
2023 NEC Now Available!
 
* * * * * * *

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

 

Member Spotlight
Radar
Radar
Los Angeles
Posts: 349
Joined: April 2004
Top Posters(30 Days)
BigB 4
triple 3
Popular Topics(Views)
303,012 Are you busy
232,123 Re: Forum
216,775 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5