Electricians: can neutral be anything but white?

[Fawken]

Guess I should chime in: what the other guy (S219) said is correct. IF the loads on the 2 independent 120Volt lines (240volts between them) are equal and they are sharing a Neutral then the current coming thru the Neutral will be a net 0 current. THIS is why having GFI Breakers on a shared neutral is not going to work (the GFIC outlet) is looking at the current going OUT (hot) and that same current coming BACK thru the white/neutral wire. It will trip when the load imbalance (current out) goes back to the panel thru the other HOT lead bypassing the Neutral RETURN circuit.

To properly wire this (you CAN still do it) however the white wire and ALL the white wires from all down stream outlets must go back thru the GFIC's "White Wire" that are feed from that GFIC outlet. This way no unbalanced neutral loads are passed back thru the other hot legs. The single white wire and two hots and green can be on different (single pole) breakers mounted side by side like a 240 breaker so they are on opposite legs of the main panel. The run of 4 wires can be from main panel board to the middle at a 4x4 boc with two GFIC breakers feeding different directions for a series of outlets as long as from that point (the GFICs) 5 wires are run keeping the white1 and white2 independent of each other just as the hots are kept independent.



Mark

Like I said, I'll do a real world test this weekend. In order for a circuit to function a pathway to ground or neutral must be complete. Question: If you cut the neutral in the scenario you describe will you see a spark/s? (let's say for this example each circuit is powering a 20A air compressor and using exactly the same current)

 

[KennyG]

As I noted earlier, I have shared neutral wiring but wouldn't do it again. I don't see any problem if you run to a junction point and then split two separate circuits. I did something a little different. I have over 30 feet of workbenches that are over 30 feet from the breaker box. I wanted a series of outlets over the benches and I wanted two 20 amp circuits I could easily reach from any point. I ran the service through a series of boxes and then wired the first box for Circuit A, the second for Circuit B, the third for Circuit A, etc. At that point I had the palm to the forehead moment when I realized I would need to have a GFCI outlet in each box because I didn't have a single point to isolate the neutrals. That's what I did and it works fine, but if I was doing it again, I would probably completely separate the two circuits at a point and then need only one GFCI in each circuit.

As usual, I've probably put myself in a situation that no one else would ever come up with.

 

[Fawken]

This is correct until you can envision alternating current as a push and pull. There will be a localized current on the neutral but the positive flow on one load returns as the negative flow on the other load rather than a current in the neutral. As we all know a 220v load will operate without a neutral so there obviously can be power transmitted without a neutral flow.

OK, now I see where there is confusion. Perhaps the "phase" nomenclature is confusing. The 60 cycle waveform for either side of the center tap is not (to my knowledge) 180 deg offset. A transformer alone cannot accomplish that. There is measurable current on the neutral or no work would be done in the circuit.

 

[grsthegreat]

ok, this is the last ill say.....good luck.

I do get tired of fixing homeowners messups. heres one i had to do today. Its especially nice to see someone run GAS pipe and gas pipe fittings into a electrical panel...then run romex in the same pipe. The state inspector failed the job....cant wonder why.

The homeowner said he had some gas pipe handy...so whats the big deal.

I had to replace the entire panel cause its an old zinsco panel whit the upside down main breaker.....down is on.

 

[Fawken]

ok, this is the last ill say.....good luck.

I do get tired of fixing homeowners messups. heres one i had to do today. Its especially nice to see someone run GAS pipe and gas pipe fittings into a electrical panel...then run romex in the same pipe. The state inspector failed the job....cant wonder why.

The homeowner said he had some gas pipe handy...so whats the big deal.

I had to replace the entire panel cause its an old zinsco panel whit the upside down main breaker.....down is on.

View attachment 433247 View attachment 433248 View attachment 433249 View attachment 433250

That looks hilarious! Here's one I had to fix a few months ago on a burger joint feeding a 20 amp hood exhaust vent:


And the fix, complete with required by OSHA safety cut-off switch:

 

[dstig1]

OK, now I see where there is confusion. Perhaps the "phase" nomenclature is confusing. The 60 cycle waveform for either side of the center tap is not (to my knowledge) 180 deg offset. A transformer alone cannot accomplish that. There is measurable current on the neutral or no work would be done in the circuit.

Well, sorry, but you are misinformed. The phases are indeed 180 deg out of phase. That is how 220v works. Note that 220 is 2x 110 - or 240 is 2x 120, depending on how pedantic you want to be - that is only possible with 180 deg phasing. So if everything is equal - and for example you are drawing 5A on one hot leg and 5 A on the other hot leg, the shared neutral will show zero current. Now keep in mind EVERYTHING must be exactly equal for this to happen. If you plug in the same load on 2 outlets that are not the same distance from the panel, the slight difference in wire resistance will probably cause some small current to show on the neutral, but it should be tiny. Nothing is ever perfect, so don't expect to see a rock solid zero amps, but it should be very close. I doubt your two fans will draw exactly the same amps, for example.

As to the point about the GFIs raised by Spiker, You cannot continue to use the same common neutral run after the GFI. You must split and use a dedicated hot and neutral from the GFI LOAD terminals from there on out. Perhaps that was not clear.

GRS - other than the dumb use of the 90 deg elbow, pipe is pipe, is it not?

 

[Fawken]

Let's just see what the Ammeter has to say about it shall we? Or do we need to get into a discussion about electron theory? As for the gas pipe- any idiot would know that's a total violation of code.

 

[KennyG]

I think we're getting into one of those confusing points where everyone is saying the same thing but not realizing it. The two sides of "220 service" are 180 degrees out of phase. If you have two identical 110 v loads on each side of a common neutral circuit, there will be no current flowing back to the box on the neutral. However there will be current flowing on a section of the neutral between the two circuits, returning through the hot sides to the box as the current alternates. The maximum flow through the section of neutral between the circuits will be equal to the current in either of the hot legs, which is why a common neutral cannot be overloaded.

Did that help anyone or did I make it worse?

 

[Fawken]

When you say "out of phase" are you talking about the 60 Hz sine wave? Not sure if it helped or not. I think a drawing starting at the transformer and going all the way through the circuit might clear things up. If the scenario you describe is true, given that most residential load boxes are relatively balanced, why not allow a very small neutral conductor (compared to the two hots) in service entrance wire?

 

[dstig1]

I put a smilie at the end!

It is true, it is exactly how it works. They sometimes do downsize the neutral for service entrance cable for this very reason. 2-2-4 for example. And Kenny's points are also correct. If you don't measure the neutral at the right point in the balanced test, then you could see current (similar to my point of using 2 outlets not the same distance from the panel, but a bit different).