3-way switch with neutral at both switches

bkinsley20 · 09-01-2008, 08:34 PM

I am building a new garage. I am trying to wire two 3-way switches. I have a supply line to each junction box because there are exterior lights that also feed from each of these boxes. I was wondering if since I have a neutral wire comming into each box if I could just use 12/2 between the switches and pick up the neutral (white) wire that is already there. Both boxes are wired to the same breaker.

SD515 · 09-01-2008, 09:33 PM

It's as much of getting the neutral to the load, as it is getting the common terminals connected....one to the source, one to the load.

3 way switch wiring:

White form the source goes directly to the load.

Black from the source goes to the common terminal of one of the 3 way switches.

Black of the load goes to the common terminal of the other 3 way switch.

The travelers get hooked to the remaining terminals.

If you have to use a white as 'hot', it has to feed a switch and be taped black at both ends.

I don't understand your scenario entirely. You say you have supply line to each junction box. What j-box? The sw box? Are these 3 ways controlling the ext lights? What boxes are wired to the same breaker?

220/221 · 09-01-2008, 11:15 PM

I wouldn't do it because unorthodox wiring always bites someone in the ass.

It would function however by using your 2 wire cable as travelers.

bkinsley20 · 09-02-2008, 12:11 AM

I have a switch box by each exterior door controlling the outside lights. Both boxes have power coming to them for the exterior lights. Both from the same circuit, from the same breaker. Then in both switch boxs I also have a 3 way switch to control the cieling lights from either door. Since the neutral in each switch box comes form the same circuit do I only need the two travelers (12/2) between the 3 way switches and 12/2 going to the cieling lights? When the neutral from the lights comes back into the second box I can connect to the already existing neutral from the supply?

theatretch85 · 09-02-2008, 02:23 AM

Actually I do believe what you are proposing would be a code violation. I don't know the code reference off hand, but it has been discussed on here before about the neutral and hot taking two different paths in the same circuit. If I can find it, I will post it back here, otherwise I am sure an electrician will be along to back this up.

joed · 09-02-2008, 03:02 PM

I blelieve it to be a violation. Don't know the exact reference but it has to do with the neutral and hot running within the same cable or raceway.

220/221 · 09-02-2008, 08:21 PM

It will function by using your 2 wire cable as travelers.

Is it a violation?

I don't think so but I really don't know.

chris75 · 09-02-2008, 08:50 PM

Its not a violation if the wiring method is NM, but it will still create unwanted EMF's.

jerryh3 · 09-02-2008, 09:29 PM

Quote:

Originally Posted by 220/221

It will function by using your 2 wire cable as travelers.

Is it a violation?

I don't think so but I really don't know.

I thought it was only a violation with metallic conduit due to inductive heating issues.

theatretch85 · 09-02-2008, 09:53 PM

As Posted by Stubbie in this thread:help with wiring ceiling fan from a switch controlled outlet

Originally Posted by Melanie337

I can appreciate that having the neutral and hot come from 2 different cables is not good wiring practice but, if they are the correct hot and matching neutral, where is the actual danger in having them separated? The statement was made that this is dangerous...so I'm just wondering "why"? Sorry to be a pain.

Quote:

Originally Posted by Stubbie

Not a pain at all, that is a very good question.

If I can add a bit here it may help. The code making panel did indeed include this "all conductors of a circuit must be in the same cable, raceway, cable tray....etc. in article 300... specifically 300.3 (A),(B) and 300.5. The intent was not wiring method or nails it was to reduce inductive heating in parallel conductors. This is a rather complicated theory but around 1990 enough documentation of fires from inductive heating lead to the addition of this section to article 300. Inductive heating tends to be more of an issue in metal raceways and any wiring method incorporating ferrous methods. The only exception to this rule is for equipment grounding conductors which are not normal current carriers for a ac circuit. And even this exception is very limited in its use.

The practice of using inductive heating by intentionally creating the magnetic fields that cause it is quite common for melting processes such as plastics.

No it is not easily created in house wiring at frequencies like 60HZ. However I Squared losses can be a real issue when magnetic fields cause a resistance effect in the magnetic fields if they become "unbalanced". Now I use that term actually out of context but it serves my purpose to easier understand. When the addition of a wire from another circuit comes in contact with the 'balanced' magnetic fields of properly paired (paralleled) conductors of the same circuit the overall field is disrupted (altered) and the result is I squared losses in the form of heat.