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#42969 - 09/30/04 08:37 PM Residential Multiwire Circuits
BigB Offline

Registered: 03/31/04
Posts: 725
Loc: Tucson, AZ USA
I am starting this thread to expand on multiwire discussion which was brought up in another post.
I use multiwire circuits all the time and I think they are a Godsend in making our jobs easier and neater. I too mark each set of hots by taping them to their corresponding neutral in the panel.
Recently I have thought up the idea of having my printshop make me up a roll of adhesive labels saying something like: "Caution: This system utilizes shared neutral conductors. Re-arrangement of breakers by unqualified persons could result in a fire hazard"

Has anyone thought of or done this? Any opinions?

As far as Joe Homeowner screwing it up, I see far worse almost daily. Just today I found a bathroom receptacle wired with some single lengths of old #18 stranded, tapped from a 20 amp circuit. I wonder how hot they'd get from a 1500 watt heater?

Any opinions on the labels?

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#42970 - 09/30/04 08:47 PM Re: Residential Multiwire Circuits
John Steinke Offline

Registered: 04/03/01
Posts: 509
Loc: Reno,Nv., USA
Considering the additional risks posed by multi-wire circuits, the construction of most romex used, and the likelihood of under-trained personnel working on residential circuits, I try to avoid them.

Even in other applications, I find myself getting away from them for power quality reasons.

I find that my love of saving wire is tempered by the effects of Murphy's law.

#42971 - 10/01/04 06:12 AM Re: Residential Multiwire Circuits
Ryan_J Offline

Registered: 08/19/03
Posts: 1355
Loc: West Jordan, Utah, USA
BigB: I think it is a great idea.
Ryan Jackson,
Salt Lake City

#42972 - 10/01/04 01:14 PM Re: Residential Multiwire Circuits
Fred Offline

Registered: 04/30/01
Posts: 461
Loc: Straughn, IN 47387
BigB, I also think they are a good idea when properly installed and marked.

#42973 - 10/01/04 01:50 PM Re: Residential Multiwire Circuits
Electricmanscott Offline

Registered: 01/12/02
Posts: 1478
Loc: Holden, MA USA
Big b good idea. I use multi wire circuits all the time. As for some one screwing them up after I am gone, Stupid is as stupid does.

#42974 - 10/01/04 03:31 PM Re: Residential Multiwire Circuits
shortcircuit Offline

Registered: 06/27/04
Posts: 608
Loc: massachusetts
BigB...I always mark the neutral in the panel so other wiremen can identify it.We all know what happens when you loose the neutral on a multiwire circuit...right


#42975 - 10/01/04 09:00 PM Re: Residential Multiwire Circuits
Active 1 Offline

Registered: 02/22/03
Posts: 684
Loc: Grayslake IL, USA
We multi wire anythig we can. I call it networking though. We never had a complaint or problem. We allways tape them together in the panel and some boxes depending on whats going on. Some panels we put the stick on numbers on the nutrals with the corisponding breaker. Other times we put the nutral near the corisponding breaker or in order. We put the networked breakers next to each other. On our homes the 1st network is always black, red, white. Then we save blue & gray for the other.

Ortganisation is the key. Some inspectors here require grooping the networks together in all boxes. I do hate going into a old panel with a pipe packed with wires going to breakers all over and nothing is marked.

I like the warning. I should put it on the panel schedules I print out.

I would add something to it like "The system utilizes shared nutral conductors TO PROVIDE BETTER ELECTRICAL EFFICIENTY." Something to make it sound more positive. Otherwise to a homeowner it might make them think you cut corners and something is not as safe as it could be.

Or maybe "Your electrical system has been ballanced to provide you with the best service. To keep the system ballanced only have a qualified person make chanegs inside service panel or branch wiering. Failure to follow this could result in overloading and a fire hazard."


#42976 - 10/02/04 01:33 PM Re: Residential Multiwire Circuits
Dave55 Offline

Registered: 05/08/04
Posts: 666
Loc: Crystal Lake, Illinois, USA
I'm with John Steinke on this one, however I think the notice is a great idea.

"I run shared-neutral circuits to save on material costs, it's not a code violation, so I save where I can."

Sarcasm aside, what benefit is there in running shared-neutrals other than saving a little wire? You can sugar-coat it any way you want.

The signs are actually a very good idea. If it were possible to say something, ANYTHING, that would keep non-electricians out of distribution panels, I'm all for it. Anyone with a screwdriver can electrocute themselves, or create a fire hazard.

My personal feelings on the matter are that someone could have a fair understanding of home wiring and still not understand the importance of having breakers in the correct positions for shared-neutral circuits.


#42977 - 10/02/04 02:30 PM Re: Residential Multiwire Circuits
iwire Offline

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Dave I do not work in dwelling units so I do not know if there are benefits other than saving money.

However on large jobs there are real benefits.

First and foremost voltage drop is much lees of a problem.

Second raceway fill / derating is much less of a problem.

As an example a entire 42 circuit panel full of two wire circuits is 84 current carrying conductors. Make the same panel all multi wire branch circuits and you have 42 current carrying conductors.

by Dave55
Sarcasm aside, what benefit is there in running shared-neutrals other than saving a little wire? You can sugar-coat it any way you want.

I do not have to sugar coat it there are real benefits to the customer by utilizing multi wire branch circuits. There is nothing 'hack' about using multi wire branch circuits.

If you run all two wire circuits in a large commercial project all that you have gained is cost to the customer.

by John
Even in other applications, I find myself getting away from them for power quality reasons

Please explain the power quality issues brought on by multi wire branch circuits.

The panel feeding the branch circuits uses a common neutral, wouldn't this create the same power quality issues?

Bob Badger
Construction & Maintenance Electrician

#42978 - 10/02/04 03:55 PM Re: Residential Multiwire Circuits
Roger Offline

Registered: 05/18/02
Posts: 1779
Loc: N.C.
John, how are Multi-Wire branch circuits served from a single winding affected by harmonic distortion?

The harmonics would be the same on both sides of zero and would cancel the same as current cancels in any equal current flow.

Power quality would be a concern other than a shared netral when talking about single phase services.

Dave, there are many reasons to use Multi-Wire circuits and yet the biggest reason not to is the "unqualified person" making a mistake.

A qualified individual will look at the conduit or cable entry before lifting a neutral, and if there is more than one ungrounded conducted present not tied to a common trip breaker, they would know this is the case.


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