ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
Do we need grounding?
by gfretwell - 04/06/24 08:32 PM
UL 508A SPACING
by tortuga - 03/30/24 07:39 PM
Increasing demand factors in residential
by tortuga - 03/28/24 05:57 PM
Portable generator question
by Steve Miller - 03/19/24 08:50 PM
240V only in a home and NEC?
by dsk - 03/19/24 06:33 AM
New in the Gallery:
This is a new one
This is a new one
by timmp, September 24
Few pics I found
Few pics I found
by timmp, August 15
Who's Online Now
0 members (), 37 guests, and 14 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: Apr 2002
Posts: 178
R
Member
Yesterday we went to a plant where some conductors melted in the conduit.There was several problems all the circuits were over loaded #12`s 20+ amps about 19 8' floresant on each cir.They have 1 1/4 conduit with 36 # 12 conductors all over loaded and the conduit is very hot.The question I have how best to explain to the electrical poeple How to size the number of circuits in a pipe.The code table c8 says they can have 45 in the pipe but I tried explaining that with the ciruits over loaded and the heat generated the fill and current carrying capasity of the wires would be less.I don`t think I did a good job with them understanding so please help us out with some examples and code articals thanks guys.We ran another 1 1/4 conduit over and that reduced the heat and we split the circuits droping the current to each circuit.

Stay up to Code with the Latest NEC:


>> 2023 NEC & Related Reference & Exam Prep
2023 NEC & Related Reference & Study Guides

Pass Your Exam the FIRST TIME with the Latest NEC & Exam Prep

>> 2020 NEC & Related Reference & Study Guides
 

Joined: Mar 2001
Posts: 2,056
R
Member
See table 310.15(B)(2)(a) for adjustment factors.
36 conductors require an ampacity adjustment that results in only 40% of the Table 310.16 values.
In your case (using the 90c column for derating purposes) .4 x 30 amps = 12 amps for #12 copper.

Joined: Jan 2001
Posts: 75
G
Member
Is that 36 ungrounded conductors plus neutrals ?

Many plants have 3Ø 4W so the neutrals would be current carrying also on circuits with ballasts.

If so, could be 35 percent derate.
30A * 0.35 = 10.5 Ampacity.


Link Copied to Clipboard
Powered by UBB.threads™ PHP Forum Software 7.7.5