ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
UL 508A SPACING
by ale348 - 03/29/24 01:09 AM
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
Do we need grounding?
by NORCAL - 03/19/24 05:11 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
1 members (Scott35), 365 guests, and 16 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: Jan 2004
Posts: 171
M
Merlin Offline OP
Member
According to 310.15(B)(6), I can feed a 120/240 single phase service with 400 MCM copper. Am I correct that for a 4 wire, 3 phase, 120/240 service that I have to derated per 310.15(B)(2)(a)? If so, I would need 500 MCM, correct? Thanks, Merlin

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: Jul 2007
Posts: 1,335
S
Member
310.15(B)(6) is for single phase dwelling units service and feeders. Since that you are bringing in a 3 phase service, you can not derate. If you were to then run single phase feeders to like apartment units, those could be derated. Otherwise no derating is allowed.


"Live Awesome!" - Kevin Carosa
Joined: Jan 2004
Posts: 171
M
Merlin Offline OP
Member
Thanks Sparky. So if that is the case, then I have to run 500 MCM conductors then. Correct?

Joined: Jul 2007
Posts: 1,335
S
Member
yep


"Live Awesome!" - Kevin Carosa
Joined: Jul 2007
Posts: 1,335
S
Member
I stand corrected, yes as far as your original yes. The service wires by code are only required to be big enough to the load caulated in Article 220. However if you are building something off of an engineer's drawing, you need to use was was spec'ed of do a RFI with the designer of record. There may be also local ordinaces. I typically size my feeders based on my main breaker size. This way if the loads increase on the future, the customer will not have to pay twice.


"Live Awesome!" - Kevin Carosa
Joined: Jan 2004
Posts: 171
M
Merlin Offline OP
Member
Am I allowed to size according to breaker size at 80%? Therefore allowing me to use 350 MCM. Or would I have to use 100% rating? Thats how I read the code one minute, but the next I'm second guessing myself!

Joined: Feb 2003
Posts: 939
F
Member
you can run at 100% however if you going to make single phase feeder network you can not reduce the neutal conductor at all espcally feeded from 3Ø supply.

Merci,Marc


Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)


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