ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
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
AFDD's coming to the UK
by Texas_Ranger - 01/17/23 07:22 PM
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
0 members (), 12 guests, and 17 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
#40076 07/11/04 11:01 PM
Joined: Jun 2004
Posts: 6
R
Junior Member
hi all
I have a question
can anybody explain me please what is derating ? when I have conductors in a raceway?
thank you

#40077 07/11/04 11:05 PM
Joined: Aug 2003
Posts: 1,374
R
Moderator
Ampacity adjustment is required when there are more than 3 current carrying conductors in a raceway. If you look at table 310.16, you will notice that that is what the table values are based on. After that, see 310.15(B)(2)(a).


Ryan Jackson,
Salt Lake City
#40078 07/12/04 08:48 AM
Joined: Dec 2002
Posts: 330
S
Member
To expand on Ryan:

When you have a single conductor carrying current there is energy lost in the form of heat. The more current, the more heat. A bare wire can handle a lot of current without any problems for the bare conductor itself because of the high melting point of the metal conductor.

But when you need to insulate the conductor from other conductors, the insulating material usually has a much lower melting point than the bare conductor itself. The insulations lower melting point becomes the limiting factor.

Taking several insulated conductors and placing them in close proximity effectively places several heat producing sources close together. Less of the heat that is generated in each conductor can disipate into the surrounding enviroment causing each conductor to run at a higher temperature. These higher operating temperature conditions combine to make it so each conductor can not carry as much current without aproaching the safety point before melting the insulation.

Shane

#40079 07/12/04 09:54 AM
Joined: Sep 2002
Posts: 1,498
Likes: 1
C
C-H Offline
Member
Shane's description is very good. I only want to add that it is usually not the melting point of the insulation that is the limit. Rather, it is the temperature which will degrade the material over a very long period of time. The melting point of PVC is at least 150C, but it will become brittle by exposure to only 100C for a long period of time.

[This message has been edited by C-H (edited 07-12-2004).]


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
timmp
timmp
Leo, IN, USA
Posts: 28
Joined: June 2004
Top Posters(30 Days)
BigB 9
triple 3
Popular Topics(Views)
302,454 Are you busy
231,865 Re: Forum
216,481 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5