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
International Wire Colour Codes
by Tjia1981
Yesterday at 09:09 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
230 or 345 kV transmission lines?
by annemarie1
10/12/16 01:23 PM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 11
HotLine1 6
renosteinke 6
ghost307 5
Potseal 4
Who's Online
1 registered (Tjia1981), 175 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#82328 - 11/05/02 04:59 AM different size breakers on multiwire branch
jdevlin Offline

Registered: 08/07/02
Posts: 402
Loc: welland ontario canada
This topic came up on another site. Is it permitted the have a multiwire circuit with a 15 amp on one branch and a 20 amp on the other branch. The neutral is a #12 wire.

2014 / 2011 NEC & Related Books and Study Guides
#82329 - 11/05/02 06:19 AM Re: different size breakers on multiwire branch
Redsy Offline

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
Never thought about it before, but I can't think of a reason not to.
(gut feeling says not to)

#82330 - 11/05/02 08:30 AM Re: different size breakers on multiwire branch
ElectricAL Offline

Registered: 10/10/01
Posts: 615
Loc: Minneapolis, MN USA
I agree Redsy.

210.4(B) requires simultaneous disconnection of the ungrounded conductors that supply stuff on a common yoke. A listed handle tie would take care of that.

I see frequent examples of a 15 A and a 20 A circuit sharing a common 12 gauge neutral in residential systems based on EMT or Flex wiring methods. In this area, 7-county Minneapolis / St. Paul, the age of installation is most commonly 1950 thru the mid-70's. In 1975, the local "all metal" requirement was relaxed to permit NM.

Perhaps the most common configuration was running a general lighting circuit with the laundry circuit.

The slight economic incentive to save on material used is still available in NM if one uses a 12/3 NM homerun with one of the ungrounded 12s on a 15 A breaker, and the rest of the 15 A circuit beyond the 12/3 on 14/2 NM.

Al Hildenbrand

#82331 - 11/05/02 04:37 PM Re: different size breakers on multiwire branch
tdhorne Offline

Registered: 03/22/01
Posts: 344
Loc: Maryland, USA
One word of caution would be that you might want to tag the fifteen amp leg of the 12/3 w Gnd in the panel to indicate that it supplies 14 gauge wiring. This is to prevent some follow on genius from supplying the 14 AWG from a replacement 20 amp breaker.
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison

#82332 - 11/08/02 01:13 AM Re: different size breakers on multiwire branch
Matt M Offline

Registered: 03/25/01
Posts: 93
Loc: Laporte, MN, USA
Just curious, but are there any instances where you would ever want or need to do this? I could maybe see it for a multi-wire that serves a single piece of utilization equipment where it is possible that the loads on each leg are far from equal, but I can't see why you would ever need or want it on a multi-wire for general purpose branch circuits.

Where this would apply to general purpose branch circuits as you suggest, we're talking the difference in price of one single #14 conductor versus the price of one single #12 conductor? Why even bother?

#82333 - 11/08/02 03:14 AM Re: different size breakers on multiwire branch
Electricmanscott Offline

Registered: 01/12/02
Posts: 1478
Loc: Holden, MA USA
It is not neccesarily the price of the materials that would drive this. I have done it because of the diffculty of running new circuits in an area. I have also used an existing wiring in remodel in this manner. For new construction I probably wouldn't bother.

#82334 - 11/08/02 09:56 AM Re: different size breakers on multiwire branch
jdevlin Offline

Registered: 08/07/02
Posts: 402
Loc: welland ontario canada
Never done it. Never even thought about. It is just something that came up on another forum.


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