Are my "semi-shared neutrals" a problem?

I just installed a pair of 3-way switches for the two lights for my basement stairway. The power goes to the switch at the top of the stairs, and the lights are fed by the switch at the bottom. However, one side of the light at the bottom of the stairway is connected to a neutral for a circuit other than the circuit that services the switch and light at the top. This configuration was not planned. Rather, I simply missed the matter of running yet another wire to be able to connect the bottom light's neutral at the top.

The two circuits involved are on opposing legs in the breaker panel.

Question: Will what I have be okay as long as I install a double-pole breaker for those two circuits? Their respective loads are each small and essentially equal.

No, this is an illegal connection and must be corrected if you want to comply with today's standards and be safe.

jar546 said:

No, this is an illegal connection and must be corrected if you want to comply with today's standards and be safe.

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Please try to help me understand what might be wrong or dangerous or whatever. Shared neutrals are not "illegal", and using a double-pole breaker for these two circuits would make it impossible for anyone to get hurt while working on either as long as the breaker is off.

If 2 separate circuits have a interconnected neutral and you shut off 1 circuit the circuit that is not off will keep the connected neutral "hot" because it is not off, it is still operating through the 2nd live circuit.

In a shared neutral, the assumption is that the two loads are nearyly balanced, thus the current in the neutral wire is small. In your case, alth0ugh your loads are small, as you describe, you have UNbalanced the load to some extent. Is is really dangerous? Maybe not. But codes are written to avoid "maybes" and protect against something that some future homeowner may do, unaware of the shared neutral.

leejosepho said:

what might be wrong or dangerous or whatever.

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It is very wrong for several reasons.

One is that unless you are going to be the only person working on the circuit no other person will understand just what is going on with the circuit and will rewire the entire circuit

Two all conductors of a circuit must be in the same raceway or cable. This stops inductive heating which can start a fire, see 300.3(B) of the NEC

The list goes on and on but the simple answer is the installation does not comply with the safety standards of today’s codes and is improperly installed.

If you were able to install the switch leg from the switches to the light it would be just as easy to install the grounded neutral with it so lets get this fixed right away.

Ever hear the term "he knows just enough to be dangerous"?

It applies here.


Although it helps to understand why, it's prudent in this case just to take the advice offered here and do whatever it takes to wire your switches correctly.

Just curious. How do you guys wire a three way switch with 2 lights in between. Do you establish a regular 3 way connection with one of the lights and then just jump to the other light. And in that case can you just keep jumping to other lights if you want more than two?

It is ALWAYS easiest to run a 3-wire between switches. To go: switch-light-light-switch; you need a 4-wire between the lights.

The physical relationship between the lights and switches is rarely a concern.

GabeS said:

Just curious. How do you guys wire a three way switch with 2 lights in between.

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A three way switch is wired no differently than any other switch. The only difference between a three way (with a four way in between) and a single pole switch is the use of travelers which alternate between the switches.

GabeS said:

Do you establish a regular 3 way connection with one of the lights and then just jump to the other light. And in that case can you just keep jumping to other lights if you want more than two?

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Yes there can be more than one light up to as many as the overcurrent device will carry.

What Lee has done if very dangerous as he will now have current flowing through conductors that are not run together. When current is flowing through only one conductor it produces heat through induction.. Any metal that surrounds this single conductor such as metal boxes, staples, connectors and such will begin to heat. The more heat that is applied the more carbon will build up and the more carbon buildup the more heat that is produced and the carbon holds this heat. If two conductors are present in the cable or raceway that carries the same current, the two conductors will cancel each other out

If there is nothing more learned by the Do-It-Yourselfer on this forum it MUST be that electricity will work even when it is installed in a very dangerous manner. There is ONLY ONE correct way to make an electrical installation that is safe to both persons and equipment and just making it work is not the correct way.
If the person making the installation must ask this question they would be better advised to leave the work to someone else.

Please try to help me understand what might be wrong or dangerous

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It is the lack of this knowledge that causes fires and death to the end user. A discussion forum is not the place for someone that does not understand the danger of electrical current to learn these dangers unless the discussion forum is set up in a classroom environment.
As many professionals have said and I must say that I agree, it is those questions that do not get asked, or an explanation of the dangers that causes someone to get hurt or cause damage to the wiring system or the building in which it is installed.

Cass said:

If 2 separate circuits have a interconnected neutral and you shut off 1 circuit the circuit that is not off will keep the connected neutral "hot" because it is not off, it is still operating through the 2nd live circuit.

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Yes, and that was my very first thought just as soon as I realized I did not have the fourth wire Speedy Petey has mentioned ... and a double-pole breaker will resolve that "still operating through the 2nd live circuit" issue.

jimbo said:

... you have UNbalanced the load to some extent. Is is really dangerous? Maybe not. But codes are written to avoid "maybes" and protect against something that some future homeowner may do, unaware of the shared neutral.

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Understood, and this is not a final installation.

jwelectric said:

It is very wrong ...

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No, just wrong (without the "very").

jwelectric said:

If you were able to install the switch leg from the switches to the light it would be just as easy to install the grounded neutral with it so lets get this fixed right away.

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You bet, and it looks like all I need to do is to get about 30' of 4-conductor Romex or whatever.

220/221 said:

Ever hear the term "he knows just enough to be dangerous"?

It applies here.

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Now there is a case of something or someone being *very* wrong! If what you have said were true, I would not be here asking questions!

220/221 said:

Although it helps to understand why, it's prudent in this case just to take the advice offered here and do whatever it takes to wire your switches correctly.

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Agreed, but I would still first have to know "Why?" in order to help assure not having to go back and change even more yet later on.

jwelectric said:

... he will now have current flowing through conductors that are not run together.

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Ah. That is yet another issue I did not know about ... and I will try to make and post a sketch to be sure I understand how things need to be.

Here is a sketch of what I have at the moment ...

I also have a bare ground connected everywhere, of course, but it is not shown in the sketch.

leejosepho said:

Here is a sketch of what I have at the moment ...

I also have a bare ground connected everywhere, of course, but it is not shown in the sketch.

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Lee have you ever heard this statement?

220/221 said:

Ever hear the term "he knows just enough to be dangerous"?

It applies here.

Click to expand...

You have a serious problem with this installation and it needs to be addressed now.

jwelectric said:

You have a serious problem with this installation ...

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Please elaborate, you old windbag!

I am trying to be sure I get this right, and you have only editorial comment to offer. Has it ever crossed your mind to actually try to be helpful?!

I have one light sharing a common, and that needs to be corrected.

What is the alleged "serious problem" you have mentioned?

Your wife is correct.

jar546 said:

See this crude drawing ...

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Wow, and I thought mine was crude!

leejosepho said:

Wow, and I thought mine was crude!

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The difference is that yours does not make any sense and I am being helpful by taking the time to provide you with crude but accurate drawings.

Heh heh....he called you an old windbag

Just fix it and everything will be right in the universe.

BTW, I DO give you credit for coming here to learn how to do it right.

This forum is for learning...Thanks jar...

leejosepho said:

Please elaborate, you old windbag! I am trying to be sure I get this right, and you have only editorial comment to offer. Has it ever crossed your mind to actually try to be helpful?!

I have one light sharing a common, and that needs to be corrected.

What is the alleged "serious problem" you have mentioned?

Your wife is correct.

Click to expand...

Okay try reading this one more time.
Slow down and read it slowly so maybe it sinks in

jwelectric said:

What Lee has done if very dangerous as he will now have current flowing through conductors that are not run together. When current is flowing through only one conductor it produces heat through induction.. Any metal that surrounds this single conductor such as metal boxes, staples, connectors and such will begin to heat. The more heat that is applied the more carbon will build up and the more carbon buildup the more heat that is produced and the carbon holds this heat. If two conductors are present in the cable or raceway that carries the same current, the two conductors will cancel each other out

If there is nothing more learned by the Do-It-Yourselfer on this forum it MUST be that electricity will work even when it is installed in a very dangerous manner. There is ONLY ONE correct way to make an electrical installation that is safe to both persons and equipment and just making it work is not the correct way.
If the person making the installation must ask this question they would be better advised to leave the work to someone else.

It is the lack of this knowledge that causes fires and death to the end user. A discussion forum is not the place for someone that does not understand the danger of electrical current to learn these dangers unless the discussion forum is set up in a classroom environment.
As many professionals have said and I must say that I agree, it is those questions that do not get asked, or an explanation of the dangers that causes someone to get hurt or cause damage to the wiring system or the building in which it is installed.

Click to expand...

I agree.

There are many things about electricity that I don't understand either.

I used to replace bath fans, NOT anymore.
I did one job that woke me up on that. There was something very different about it, and I was getting small shocks. I realized that I was clueless. That was the last one I did for anyone.

I don't know what the guy before me had done, but it was pretty weird.
And I wouldn't to this day, know what the right question would be.