Neutrals to remain separate?

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jjhoward

jjhoward

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Location
Northern NJ
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Owner TJ Electric
Hello All,

A 4-gang box has a 120V power feed for lights A & B(standard toggle switches) and there are also two 3-way switches in this box for ligths C & D. The two 3-way switches have their commons feeding the switched power to C & D. The other end of the 3-way circuit (on the other side fo the room) has the power feed, a different circuit than the power feed in this box. Should the neutrals for lights A&B and C&D be separate?

Thank you for your wisdom!
 
Re: Neutrals to remain separate?

Yes, don't hook all neutrals together, this is dangerous. Keep neutrals with their respective circuits only.
 
Re: Neutrals to remain separate?

I would say yes just to avoid over heating of the neutral if the two hots ended up being on the same phase.
 
Re: Neutrals to remain separate?

With all of these lights on here, (there are actually flood lights) we would be pulling less than 800 watts. At 120V that is ~7 amps. If these differnt neutrals were tied together (12 awg wire on 20 amp breakers) would that 7 amps be a problem? Sure there are other loads on both circuits but small stuff, more lights. Are there other problems with tying these different neutrals together? The return current could get you if you think the circuit is off. Should these two circuit not even be in the same box??
 
Re: Neutrals to remain separate?

There is no problem with them being in the same box as they are from the same source. But, why would you want to even tie them together??? If it's 3 phase and you're using phases a,b,and c with a single neutral with balanced loads, that's fine. But it sounds like this is not your case. What is your reasoning for wanting to tie these neutrals together? You're creating a dangerous situation for the next guy.
 
Re: Neutrals to remain separate?

Hi Bruce,
No, I don't want to tie these together. I am trying to understand the WHY of not doing it.
Thank you.
 
Re: Neutrals to remain separate?

Well you already stated one good reason, unless the breaker is a 2 pole or 2 singles mechanically tied together, you're creating the possibility of return current surprising someone when working on the circuit in the future. Another is if you're just randomly tying neutrals together in junction boxes like I've seen some guys do, both circuits could be originating from the same phase which would add the currents together and you may overload and overheat the neutral possible causing a fire as the neutral would have no overcurrent protection. Sharing neutrals is very common, don't get me wrong, it's done all the time in 3 phase systems. Just make sure you know and understand exactly what you're doing when sharing a neutral. If it's done wrong, it can lead to dangerous situations for personnel and can be damaging to electronics and equipment if precautions are not taken. Again, if all code rules are followed and precautions are taken, I have no problem with shared neutrals.
 
Re: Neutrals to remain separate?

Thank you for the info. When my helper asked me about this today I told him to identify the neutrals and keep the two circuits seperate. Tomorrow we will discuss.

Joe
 
Re: Neutrals to remain separate?

Oh that's good to know. I guess I can't site a code violation here but I think some guys just tie em all together cause they figure there all going back to the same place anyway. I couldn't even count the times I've seen this done by area "handymen". Either that or making neutral to ground bonds at load side equipment, handymen are famous for that. Most of em will look at you like you have two heads when you tell em that's wrong :roll:
 
Re: Neutrals to remain separate?

Tying different neutrals together or using the hot lead of 1 circuit and the neutral of another circuit to supply a load is what I call haywiring. David Eli Shapiro in his book Old Electrical Wiring calls it the Splicebox From H#!!.
 
Re: Neutrals to remain separate?

In addition to the above, backfeeding on the neutral can be a problem. I don't really have enough of a grasp to explain where the electrons are going in this situation, but I've encountered and fixed this problem without understanding it fully.

Trying to figure out how a backfeed is operating (for me) is like doing taxes on a pogo stick. :D

At any rate, the neutrals tied together can afford the opportunity for the light to glow slightly when the switching is "off." Not cool. :D

[ April 14, 2005, 08:18 AM: Message edited by: georgestolz ]
 
Re: Neutrals to remain separate?

Originally posted by jjhoward:
... A 4-gang box has a 120V power feed for lights A & B(standard toggle switches) and there are also two 3-way switches in this box for ligths C & D. The two 3-way switches have their commons feeding the switched power to C & D. The other end of the 3-way circuit (on the other side fo the room) has the power feed ...
Click to expand...
A question for the residential SMEs:

First, other than my own remodels, I am not a house roper. Keeping that in mind, my inclination is to always pull the feed to the lighting outlet, then run the switch leg out to the sw location. High probability of oddball exceptions noted.

Is that a standard/acceptable/good/useless method?

carl
 
Re: Neutrals to remain separate?

typically when I wire a house I use my switchbox for my homerun then feed my receps in that room from the sw box. is there anything wrong with a 2 wire return my answear would be no I just did a remodel and did just that hit the fan with power then ran the power to my switch on my white wire tagged it black and put a cut piece of sheating on that wire labeld hot so theres no confusion for the next guy
 
Re: Neutrals to remain separate?

In addition to the above, out of circuit grounded conductors will cause GFCI's to trip and cause interference on sensitive equipment. This is a MAJOR cause of power quality problems.
 
Re: Neutrals to remain separate?

Originally posted by coulter:
Is that a standard/acceptable/good/useless method?
Click to expand...
It's a good method to use sparingly, IMO. I'm faster stripping out a regular switch at waist level than I am a farmered light over my head.

There's nothing wrong with it, but it could be faster (and less "arms in the air" time) to pull the power to the switch. In my opinion. :)
 
Re: Neutrals to remain separate?

Twenty years ago I flipped off a breaker on an outlet circuit, and as I was removing one neutral from the old outlet, put myself into the back side of another circuit. I picked myself up about 10 feet away. I make sure now not only that I use one neutral per circuit, and pigtail the fixtures so they are not "in the circuit", but I check for other feeds to the neutral.
 
Re: Neutrals to remain separate?

EMF...The current on one neutral may be less than on the other circuit and there would be no cancellation. It would be possible depending on circuit resistance. Lets say two circuits 7 amps each; it is feasible for there to be 4 amps on one neutral and 10 on the other. This lack of balanced current between the neutral and the phase conductor will result in EMF in the vicinity of the branch circuits. Which can, cause power quality issues; GFCI nuisance tripping (if the circuits are GFCI protected) and if the homeowner is EMF concerned a major headache for you. With higher currents it is possible to have thermal problems where the conductors enter the panel, due to inductance. (I think it is inductance causing this problem I will check my books when I return to my office.

And there is also a major problem that during trouble shooting this circuit at some later date an electrician might open this splice and with only one cuircuit off get shocked, if he/she was to get between the neutral for the energized circuit and the load for that circuit.

And while any of the above may seem a bit of a stretch do you want all of the above hanging over your head.
 
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