ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
Thought this was funny
by Ronny - 12/03/20 06:08 PM
From an outsider- How does tipping work?
by gfretwell - 12/02/20 02:38 PM
Happy Thanksgiving
by Trumpy - 12/02/20 04:11 AM
Where is Everyone?
by Trumpy - 12/02/20 03:51 AM
What does your work place look like?
by Trumpy - 12/02/20 03:42 AM
New in the Gallery:
Facebook follies, bad wiring
FPE in Germany pt.2
Who's Online Now
1 registered members (Ronny), 25 guests, and 9 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
derating #40076 07/11/04 11:01 PM
Joined: Jun 2004
Posts: 6
R
ronaldsax Offline OP
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

Work Gear for Electricians and the Trades
Re: derating #40077 07/11/04 11:05 PM
Joined: Aug 2003
Posts: 1,374
R
Ryan_J Offline
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
Re: derating #40078 07/12/04 08:48 AM
Joined: Dec 2002
Posts: 314
S
sabrown Offline
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

Re: derating #40079 07/12/04 09:54 AM
Joined: Sep 2002
Posts: 1,497
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).]


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
RH1
RH1
California
Posts: 22
Joined: August 2009
Show All Member Profiles 
Top Posters(30 Days)
Trumpy 20
Popular Topics(Views)
272,207 Are you busy
206,095 Re: Forum
194,097 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3