How Many Circuits on One Neutral

[Daryl Henderson]

How may different circuits can you use with one neutral?

110v and 220v both, and can you use a common neutral with both voltage(s).

I am using 12ga for the 110 circuits and 10ga for the 220 circuits.

All in 3/4 EMT with the longest run being 55-60ft.

[Leo Graywacz]

Single phase circuits require you to use a neutral for each hot when using 120vac. If you are running 220vac circuits you usually don't need a neutral unless the machine specifically calls for it, usually if it has light bulbs.

If it is a 3 phase circuit you can have 3 hots per neutral as long as you are using the A, B & C phases for each neutral.

A neutral is a current carrying conductor and must be the same size as the hot. The reason you can use 3 hots on a 3 phase circuit is because of the 120º differences between the phases.

[Daryl Henderson]

How many "hot" circuits can you have with one neutral in a series?

[Leo Graywacz]

I don't understand what you mean by series.

All circuits in a system are run parallel. You can only have one neutral per circuit in a single phase system, it is a current carrying conductor. If you use one neutral with two circuits you can exceed the capacity of the conductor and damage the conductor.

In a 3 phase system you can have 3 hots on a single neutral because the current is 120º out of phase from each other and won't add up like they do in a single phase system.

What is it you are trying to wire and why do you only want to run less than the required neutrals?

[Daryl Henderson]

Everything is single phase. If I have four separate "hot" wires in on conduit each going to a duplex recep, can I use one neutral in the conduit and splice to each duplex recep?

Do I need to run a separate neutral for each circuit?

[Leo Graywacz]

Seperate neutrals for each circuit. You do realize that you can only put so many conductors in a conduit, right? You can't just stuff it to capacity.

[Daryl Henderson]

Yes, I was just using that as an example.

Thanks for the info.

[Leo Graywacz]

Be safe. :cool:

[Rollie Meyers]

As long as the 2-legs of a circuit stays on opposite legs they can share a neutral, put 2 on the same leg & sharing the neutral & it can burn up the neut.BTW ,this is called a multi-wire circuit & if installed correctly is safe & code compliant, if your on the 2008 NEC® a 2-pole circuit breaker is required, prev. editions only require a 2-pole C/B if both parts of a multi-wire circuit share the same yoke of a wiring device.

[Leo Graywacz]

The reason I recommended the neutral for each circuit is he sounds like he is trying to use 220 and 120 volt circuits and share neutrals between them.

If you use a 2 pole breaker you can use one neutral for that circuit. If you don't know what you are doing with wiring a circuit you should n't be doing it. Using the single nuetral is going to be the safest and surest way of not violating and of the NEC.

[Von Bickley]

Leo and Rollie are exactly right on their statements but I would also recomend that you don't do it. I don't like to see circuits that share a neutral and you will not be able to have ground fault receptacles on those circuits if you ever need to install them.

[Rick Christopherson]

The reason I recommended the neutral for each circuit is he sounds like he is trying to use 220 and 120 volt circuits and share neutrals between them.

If you use a 2 pole breaker you can use one neutral for that circuit. If you don't know what you are doing with wiring a circuit you should n't be doing it. Using the single nuetral is going to be the safest and surest way of not violating and of the NEC.I can understand your concern that the original poster didn't understand what a MWBC is, but that is not what you told him. I think it is wrong to deliberately misinform someone, regardless of the reasons.

A multiwire branch circuit is where the A-phase and B-phase hots share the same neutral wire. Because the two circuits are on opposing phases, the current through the neutral is only the imbalance between the two loads. If you mistakenly put both circuits on the same phase, then the current in the neutral wire will be the total sum of both circuits, and this will overload the conductor.

One aspect about this that is pertinent to the O.P. is that the neutral of a MWBC is not counted as a current carrying conductor, so it does permit more wires in the same limited conduit. It also results in less physical heating of that conduit, as opposed to using individual neutral wires.

I don't like seeing MWBC in most residential situations because they have limited value, but in commercial or conduit installations, they do have a benefit.

[Leo Graywacz]

There are to many people on these forums that really don't have a clue as to how to do wiring, I don't know if he has experience or not. I will help them with some simple stuff but nothing complex. He asked the same question a few times which led me to believe that he hadn't done much wiring before. So I would rather give him the safe way. It will get the job done and cost him a bit more in wiring costs. And it will still be correct.

[Rick Christopherson]

There are to many people on these forums that really don't have a clue as to how to do wiring, I don't know if he has experience or not. I will help them with some simple stuff but nothing complex. He asked the same question a few times which led me to believe that he hadn't done much wiring before. So I would rather give him the safe way. It will get the job done and cost him a bit more in wiring costs. And it will still be correct.Yes, I understand your point and I agree with your point. What I do not agree with is lying to someone, even if it is to protect them.

There is nothing wrong with having moral standards that prevent you from giving information to someone that might cause them injury. However, in the face of that moral standard, you should have simply refrained from answering at all, instead of lying. You could have told the poster that based on his question he should not be attempting his own wiring. Or you could have taken the extra time to teach him what he did not know. Of all the choices available, misleading someone is the worst choice to make.

[Mark Bosse]

If you are doing the work as an unlicensed electrician:

Pull one neutral with each conductor for 110 v circuits. It should be the same gauge and insulation class.

If you are pulling a 220 v circuit, carry a neutral with you (again, same gauge and insulation class). Not every machine will require it, but many will. It is a royal pain if you have to do a complex re-pull to make a DRO work for example.

If you are trying to split a 220 v circuit into two 110 v cuircuits, be sure that you talk to an electrician. Some of what I am reading here on this thread is wrong.

As an example, it is not enough that the two 110 v legs come from separate bus bars on a single phase system in order for you to use only a single neutral. If the balance between the two 110v sides is seriously out of balance (one a motor and one a battery charger for example - a very common problem), your electrician may want to either use a heavier neutral or carry two. This can be a heat issue.

A second example, most of you don't understand insulation classes at all. You most certainly need to learn about this before you advise people what wire they can stuff into a tube.

Before the "Home Depot - How To Experts" get on me again, remember please that the major work of the designer is load balance and heat control. You can be 100% code compliant and still produce too much heat. Your "How To" books are not enough information for you to do design work.

If you are doing something tricky, pay the man and get some help.

[Jason Roehl]

Mark, if one neutral is serving two circuits connected to opposite legs of a service, the currents are subtractive. In other words, a neutral serving just once circuit with a motor running is carrying more current than a neutral serving a motor on one leg and a battery charger on the other--the total current would be the amperage of the motor MINUS the amperage of the battery charger. The amperage on that neutral can never exceed the amperage of the breakers on either circuit, again, provided those two breakers are on different legs. Using a double breaker with the two switches tied together assures this in most panels as top-bottom adjacent spaces are on different legs in typical 240V residential service.

[Chris Padilla]

If you are trying to split a 220 v circuit into two 110 v cuircuits, be sure that you talk to an electrician. Some of what I am reading here on this thread is wrong.

As an example, it is not enough that the two 110 v legs come from separate bus bars on a single phase system in order for you to use only a single neutral. If the balance between the two 110v sides is seriously out of balance (one a motor and one a battery charger for example - a very common problem), your electrician may want to either use a heavier neutral or carry two. This can be a heat issue.

Well, Jason just called you out as this is wrong. :)


Before the "Home Depot - How To Experts" get on me again, remember please that the major work of the designer is load balance and heat control. You can be 100% code compliant and still produce too much heat. Your "How To" books are not enough information for you to do design work.

I suspect you are in that category, too, Mark. :p ;)

[Steve Clardy]

Wheres the popcorn. Maybe I can learn something too.