The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!


2017 NEC and Related
2017 NEC
Now Available!

Recent Posts
Parking lot pole light swap....
by gfretwell
10/24/16 08:46 PM
International Wire Colour Codes
by Tjia1981
10/23/16 12:08 PM
Son of Sparky
by HotLine1
10/20/16 07:43 PM
Speaking of Plugmold ...
by gfretwell
10/17/16 02:37 PM
Broken battery charger? Check for cobwebs!
by gfretwell
10/17/16 02:30 PM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 14
HotLine1 7
ghost307 7
renosteinke 6
Potseal 4
Who's Online
0 registered (), 252 Guests and 5 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#84677 - 04/20/03 06:31 PM wire sizing
ga.sparky56 Offline

Registered: 11/24/02
Posts: 582
Loc: young harris georgia usa
I need some help guys. I got into a friendly argument with an EC friend of mine about sizing subfeed conductors. House has 200a MB 40 space panel,adding 100a breaker to feed 100a MB panel in detached garage.I say the feeder wires must be sized using 310.16. He says you can use table 310.15(B)(6). Who eats the crow sandwich? Russell

2014 / 2011 NEC & Related Books and Study Guides
#84678 - 04/20/03 06:59 PM Re: wire sizing
caselec Offline

Registered: 04/14/02
Posts: 557
Loc: San Jose, CA
Table 310.15(B)(6) Is for the service entrance conductors, service lateral conductors, and feeder conductors that serve as the main power feeder to a dwelling unit. A garage is not a dwelling!

Curt Swartz

#84679 - 04/20/03 07:17 PM Re: wire sizing
russ m Offline

Registered: 02/22/03
Posts: 165
Loc: Burbank,IL,USA

#84680 - 04/20/03 07:44 PM Re: wire sizing
ga.sparky56 Offline

Registered: 11/24/02
Posts: 582
Loc: young harris georgia usa
Ok,this means that no subpanel fed from this 200a panel in the house could be fed with the reduced wire sizes in 310.15(b)(6). This includes subpanels inside the house itself, correct? Thanks for your replies! Russell

#84681 - 04/21/03 04:05 AM Re: wire sizing
Redsy Offline

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
Have him read 310.15(6).
See if he still disagrees.
I,ve seen this mistake several times.
The easiest thing might be to install a smaller feeder breaker (80-90 amp?), if the load permits it.

#84682 - 04/22/03 05:54 PM Re: wire sizing
Steve T Offline

Registered: 02/14/01
Posts: 312
Loc: Oak Park, IL, USA
When the code allowing downsizing the wiring to feed the dwelling unit was submitted, I believe the data used to support this was utility actual power usage from monthly meter readings. (Please correct me if I'm wrong on this anybody.)

Since the feed to garages is not metered and thus not included as part of the data, garages are not allowed to use this table, only the feed for the house.


ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals