Shared neutral wires, split-wired receptacles, multi-wired branch circuit wiring:

This article provides an explanation of electrical wiring and safety defects regarding split-wired (multi-wired or shared neutral) electrical receptacles. We include electrical code citations for mutliwire circuits.

Split Wired Electrical Receptacles

These questions & answers about wiring, using, testing multi-wire shared-neutral branch circuit electrical wiring were posted originally at MULTI-WIRE CIRCUITS - please be sure to review the explanation, hazards, anbd advice given there.

Comment: by Christopher Jones clarify: the hot wires are on two different "poles" not really two different "phases"

The author of the article incorrectly describes the two "hot" wires as having different "phases".

He should instead say that they are on different "poles", which is why there is voltage potential between the two, despite them being on the same "phase".

A multi-phase panel in a one- or two-family residence would be very unusual, and perhaps would owe its existence to a homeowner with a nice woodworking shop with three-phase motors on a table saw, etc. 2014-10-28

Reply by (mod) -

Thanks Chris, duly noted.

On 2018-12-06 by (mod) - lost power, no breakers tripped

I would start my double checking the wiring at the GFCI that you think is only protecting itself. If other receptacles are wired Downstream from it and the GFCI trips that will trip off the ones Downstream as well. Or you could just try resetting the GFCI to see if that restores power.

On 2018-12-05 by jim dunn

had power go out in our bedroom to the outlet circuit which consists of 8 outlets-7 around the room with 1 on the wall immediately outside the door opposite one of the bedroom receptacles.

No breakers were tripped, in fact, no breaker(s) identified for the circuit in question. One gfci on deck outside opposite another inside receptacle was tripped. The gfci is wired to protect itself only. In addition, there are 2 switches associated with the 2 closets(lights only) and there is no power to them either.

I looked extensively for a subpanel, found none. Went around the circuit to determine configuration, checked for connection integrity, and find the power source.

Everything told me the fault was due to the power source/feeder and I found the incoming power line in a receptacle which had 3 cables in it.

2 of these cables(2 conductor with ground) were traced to their next-in line devices 1 to one of the switches, the other to the next receptacle.

The 3rd was the incoming power which, was not present(actually around 1/2 Vac).

But now, how do I find the other end of this feeder cable?

Its not directly terminated at the panel as there is no breaker that I can find that is for this bedroom circuit. Even tho I didn't see any breaker labled as such, I reset them all.

Since by my reasoning, the fault must be with the power somewhere on this feeder more than likely its connection to a source other than the panel, where can I go next? The cable comes into the receptacle through one of the holes in the top of the receptacle, and that's it. How can I continue going up the line to find the problem?

I don't know where this cable comes from, am I going to have to bring in a new power line and 'cap off ' the old one ?

On 2018-04-12 by (mod) -

Ron

Please see PROPER RECEPTACLES for 30A 240VAC CIRCUITS

What all of this code talk means is that on a 30A circuit your receptacles must be rated for 30A too.

On 2018-04-12 by Ron

I think you got the responses confused. I was the "anonymous" response below to "Cortese" suggesting HE try the Leviton receptacle for his question.

MY QUESTION was about multiple outlets on a multi wire branch circuit is repeated here:
I have a small shop in my garage with three 240v appliances (dust collector - 3A, heater - 12A, table saw - 9A). Can I create a single 30A branch circuit to pick up the outlets for all these appliances in a single circuit?

if possible, I'd like to use 20A outlets on the 30A circuit (nothing plugged in would come standard with a 30A plug, so I'd have to re-plug all 3 of the appliances I listed above)

On 2018-04-12 by Anonymous

@Cortese,
yes, look into the Leviton 5842-i receptacle, it will wire off a 20A, 4 wire branch circuit and deliver 220v and 110v to different plugs on the outlet i referenced. total amperage pulled from both the 120v side and the 240v side cannot be more than the 20A breaker. (so if you had an appliance that pulled 12A on the 240v outlet and an appliance that pulled 10A on the 120v outlet, the breaker would trip)

On 2017-09-13 by Cortese

Could you add a 240V receptacle in conjunction with a 120V duplex running off a multi wire branch circuit?

On 2017-07-26 by (mod) -

Yetta, I don't know as I'm confused by the question as you put it. But I can say good luck on your test - right?

On 2017-07-25 by Yetta

What branch circuit consist of two or more underground conductors have a potential difference between them and a grounding conductor have an equal potential difference between it and each ground conductor of the circuit and that is connected to the neutral or grounded conductor of the system

Question: interpreting the electrical code on shared neutral circuits

(July 28, 2015) George said:

I see in this article but only in one place NEC 2008 is multi-wire circuitry referred-to.

Could you please help to understand if shared neutral is still permitted for the same definition of multiwire branch circuit (as two or more hots and one? neutral)by the NEC 2011 and NEC 2014 where in Article 200.4 is written like as follows:

Neutral conductors shall not be used for more than one branch circuit, for more than one multiwire branch circuit, or for more than one set of ungrounded feeder conductors unless specifically permitted in this Code. I would be sure that is still permitted one neutral for one multiwire branch circuits, but it is written in plural - Neutral conductorSSS.

But if to understand in this way - feeders' hots (circuits) should be with dedicated neutrals too. Could you please explain if one shared neutral is still permitted for one multiwire branch circuit and in what cases? I would so much appreciate your help. Thanks, George.

Reply:

Yes George I share your interpreation - one neutral can be shared on one multiwire circuit by the NEC. The issue is that some devices such as AFCIs and GFCI's do not perform well on shared neutral circuits

Question: Son's stripper friends are overloading electrical outlets

(Oct 7, 2015) Jimmy Ray said:

In our trailer, my son moved in two strippers from the local club. I was against this but he did it anyway.

They try to plug in all kinds of stuff in the two outlets in the bedroom. This is blowing the fuses and fuses ain't cheap. Can i run a double 12/2 to a outlet so they can plug all that in without popping the fuse?

Reply:

Jimmy Ray,

Running 12/2 wires to a dedicated electrical outlet is a reasonable solution to the overload probelm you describe PROVIDED that the circuit is properly installed and protected, that is code-compliant. It will need its own 20-Amp breaker or fuse, and you'll want to use an electrical receptacle ("outlet" or "wall plug") rated for 20-Amps.

See SIZE of WIRE REQUIRED for ELECTRICAL RECEPTACLES https://InspectAPedia.com/electric/Electrical_Outlet_Wire_Size.php

See ELECTRICAL RECEPTACLE TYPES https://InspectAPedia.com/electric/Electrical_Outlet_Types.php

properly wired, routed, grounded, etc.

Question: using 50A 240V outlet & 120V outlets on the same circuit?

(Jan 25, 2016) DaveH said:

I'm wiring a small woodworking shop and providing multiple metal surface mount outlets (fed by EMT).

Is it allowable to wire a multiwire branch circuit that provides both a single 50A 240 outlet and two 120 outlets (one on each phase) as long as I have a 2 pole tied breaker feeding the circuit.

Furthermore is it allowable to have two surface mount outlet boxes touching each other side-by-side so the wiring from the 240 outlet can be split and feed the 120 outlets in the adjacent box. Or do I have to do the single 240, exit the box, go through a short length of EMT, enter another box and then be split out to the two 120 outlets.

I've spent hours going through my code book and I'm pretty sure the answer to the first question is "yes" but I can't find if side-by-side outlet boxes are allowable.
Thanks

Reply: no

I'm afraid, I'm very afraid. The placement of a 120V receptacle (normally a 15A or 20A circuit) on a 50-Amp electrical circuit is asking for a building fire, or for users, shock, or injury or worse. A short circuit in wiring or a defective appliance plugged into one of those 120V receptacles is being fed 50Amps rather than being limited to the proper 15 or 20 Amps of current.

Don't do it.

Original reply:

I'm not sure what code says about the mixed-circuit you describe but it's a hybrid that sounds totally unsafe and unacceptable to me.

Certainly if the 2-pole breaker has a common internal trip mechanism then an overcurrent on either leg would trip the whole breaker off. But you're using a 50A breaker to power not just a 240V receptacle but also two 120VAC receptacles.

Those "normal" 120VAC receptacles typically are on 15A or 20A electrical circuits. Not a 50A circuit. You may be under-protecting them by potentially allowing too much current to flow to devices plugged into them.

Question: no multiwire branch circuits on solar powered systems

(Apr 12, 2016) Ron Swoverland said:
doing solar you can't use multi branch circuits

Reply:

Ron:

Can you give me some details of what you mean, where the problem occurs, what sort of circuits you refer-to?

BTW I agree that multiwire circuits can be trouble. In particular, both GFCIs and AFCIs will not work properly on a shared neutral circuit. But to be clear, shared neutral wires, properly connected, are certainly permitted by the electrical code.

Question: over protection vs under-protection of an electrical "outlet"

2017/02/01 Dave H said:

My understanding was the panel breaker is intended to protect the wall wiring and not necessarily the appliance - thus you could over-protect a outlet but not under-protect an outlet.
Having said that, I can see what you mean by allowing too much current to go through a 20A outlet.

You could melt the outlet before the breaker would pop, the wall wiring (being sized for it) could handle the current but the outlet couldnt.

Looks like I'll need to run separate 240 and 120 runs to each outlet. love - it would have saved me a lot of wire runs.

Reply:

If you mean that it's ok to put a 20A rated receptacle on a 15A circuit because you've over-protected the outlet by limiting its current to just 15 Amps, that sounds reasonable to me, but I'd not like to see a 20A receptacle

(See ELECTRICAL RECEPTACLE TYPES)

on that 15A circuit for a different reason: the receptacle's physical appearance (that extra horizontal slot) tells some users that it's on a 20A circuit - risking repeated nuisance tripping of the 15A circuit.

I certainly agree that putting a 15A receptacle on a 20A circuit could be inviting trouble for the opposite reason: you may overheat receptacle components.

The worries in an earlier question about spinning off 15A or 20A 120V circuits off of a 50A circuit is a still more serious fire hazard.

On 2015-01-05 by (mod) -

Yes and no Anon. You might find that since a kitchen counter receptacle must be GFCI protected you might get GFCI faults when you feed other devices from one leg of a multiwire circuit.

We've reported as have many electricians and some inspectors that there are functional issues when we use shared neutral circuits on GFCI devices.

On 2015-01-05 by Anonymous

Can you connect a light ckt to a dedicated Multi-wire circuit .
In this case a kitchen counter ckt

(Kitchen Counter receptacle which feeds to a double pole 120/240 at panel )
Asking whether I could use the neutral and one of the hot legs of this multi-wire ckt to extend to a light ckt?

On 2014-10-28 by Christopher Jones

The author of the article incorrectly describes the two "hot" wires as having different "phases".

He should instead say that they are on different "poles", which is why there is voltage potential between the two, despite them being on the same "phase".

A multi-phase panel in a one- or two-family residence would be very unusual, and perhaps would owe its existence to a homeowner with a nice woodworking shop with three-phase motors on a table saw, etc.

On 2014-08-11 17:54:14.774870 by (mod) -

Dick,

Rather than withdraw the post completely, send me some photos (Email is at our CONTACT link), and we can edit your findings into data that will help other readers. Daniel

On 2014-08-09 23:16:16.615020 by Dick N

Just got another one, different mfg. It also has the top & bottom separate including the ground. I'm almost ready to withdraw my original post.

On 2014-07-20 00:37:12.261550 by (mod) -

Dick

If I were back in our lab I'd have disassembled one of the adapters you describe so as to map and photograph its guts. Perhaps you could do that. Use our CONTACT link to send photos and details if you're so inclined.

On 2014-07-19 23:07:26.445170 by Dick N

I might have shot from the hip here. Just tested one, and its two halves were isolated - even the grounds!

On 2014-07-15 01:20:42.400300 by (mod) -

Dick you raise an interesting and important point. We'll research this matter further and write the topic into the article above. I haven't disassembled one of the adapters you describe - if it's internal wiring splits its power, taking the upper receptacle power source to 3 receptacles in the adapter and the lower etc. the device might not create teh 240V short you describe.

If you can help with any research citations or code offerings on the matter that'd be great.

These authors have reported on multiwire circuit hazards (but need deeper review)

Mullin, Ray, and Phil Simmons. Electrical wiring residential. Cengage Learning, 2014.

HICKES, WF, CMJ OUDAR, BG LIPTÁK, and A. ROHR. "7.2 Electrical and Intrinsic Safety." (2003).

Kardon, Redwood, and Douglas Hansen. Electrical: An Illustrated Guide to Wiring a Safe House. Taunton Press, 2008.

I'll see what Mr. Kardon has to suggest.

On 2014-07-14 16:11:16.831860 by Dick N

IMO,the common availability of multi- (usually 6-) outlet adapters makes it unsafe to power the two halves of a duplex outlet from different busses. These adapters tie the two outlets in parallel - the customer would create a 240v short upon plugging it in. Moreover, even if the two halves were powered from the same bus, both circuit breakers would be paralleled.

On 2012-10-23 02:30:42.450471 by Jose A. Guillen

If i have a receptacle and i break the tabs off and my breaker trips will one part stay energized or am i understanding this wrong as to why i need a handle tie.

On 2012-02-16 17:57:03.989928 by bill laster

does a dedicated electrical circuits require independent hot and nuteral or just hot? So if I had two seperate dedicated circuits in one conduit line I would have 4 wires two hot snd two seoeraste neutral lines pluse a single ground.

On 2011-08-01 19:54:17.539064 by (mod) -

Both Messrs. Garafano and Genander have offered important and helpful comments (below) about possible hazards with multiwire electrical circuits.

Mr. Garafano's suggestion that there be clear notice at the panel of the multiwire circuit might, unfortunately, not be enough to protect from harm someone working on electrical wiring elsewhere in the building. We've had just this happen - a circuit was shut down for electrical work but a shared neutral actually sent current through that circuit's neutral and even its grounding conductor wires to shock the worker when its companion multiwire circuit was in active use.

On 2011-08-01 04:25:51.279517 by Lawrence Genander

There can be a large unbalance of voltage between ground and neutral in a three phase sys. such as
277 volt liteing even if the breaker for said circuit is "OFF" there will also be enough current
there to electro-cute a person getting between the ground/s and neutrals.

On 2011-08-01 04:03:18.243580 by Raymond Garafano

It is unsafe to use branch fuses on a multi-wire circuit be they edison screw fuses or cartridge
due to one fuse blows and the person checks voltage across the two hot legs and sees there is no
voltage but if they don't check from both fuses to ground or neutral they would not see there is
120 volts still present, unless a very clear notice is made at the panel to inform users of that
circuit to remove BOTH fuses before doing work on said circuit

...

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