Electricians: can neutral be anything but white?

[Fawken]

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).

I'm willing to test it, and I could be wrong and will fully admit it. For a myriad of reasons (not the least of which is I value my power tools) I would not ever consider wiring a shop like this. What is he going to use in each box for continuing the neutral? A wire nut? If after the first GFI you have to run dedicated neutrals anyway- what is the point? If the neutral gets interrupted in the slightest he'll have 220 coursing through his tools.

 

[grsthegreat]

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:
View attachment 433256 View attachment 433257 View attachment 433258

And the fix, complete with required by OSHA safety cut-off switch:
View attachment 433259

Holy cow.... Guess he ran out of gas pipe

 

[GPintheMitten]

I'm willing to test it, and I could be wrong and will fully admit it. For a myriad of reasons (not the least of which is I value my power tools) I would not ever consider wiring a shop like this. What is he going to use in each box for continuing the neutral? A wire nut? If after the first GFI you have to run dedicated neutrals anyway- what is the point? If the neutral gets interrupted in the slightest he'll have 220 coursing through his tools.

If the neutral comes loose, how will there be a completed circuit at the outlet that his power tool is plugged into? He'll have a black 120 volt wire connected and no other wire connected. Seems to me he will have zero volts, not 220.

 

[aczlan]

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?

With 220, you have two sine waves that are 180 degrees out of phase, so (relative to neutral), one will be at +110v and the other will be at -110v and they swap places 60 times per second.
As for a smaller neutral for the service entrance, I suspect that they don't allow it because the load may not be balanced.

When you do the test, you should see current in the neutral off of each fan, but little or no current at the connection to the power outlet or panel (after both neutrals are connected together.

Aaron Z

 

[LD1]

I did give you one. You can't put arc fault breakers on a shared neutral.

It may not apply to your situation. But, it is a legitimate reason.

I have no plans of using AF breakers. Just standard breakers

I'll test it with an ammeter this weekend and post an actual picture of the read-out with two identical fans on the same speed setting, sharing a neutral on opposite poles of the center tap.

Looking forward to the test.

I (and I dont think anyone else) is saying that there will never be amperage on the neutral. Just saying that it will never see more than 20A.

I assume this is how you are going to conduct your test:

Simple 2 hots and a N going out to two receps. First recep gets line 1, second recep gets line 2. Both use the same neutral

It is unlikely that you will find two things or fans that will pull an identical load. So lets say you load line 1 up with 5A and load line 2 up with 6A. The neutral wire BETWEEN the outlets will read 6A

The neutral wire between the box and the first outlet will read 1A. Because the 5A from outlet 1 is SUBTRACTED from the 6A from outlet since the hots are on different phases.

I think you are assuming they get added together. But that would only be the case if the two hots were on the same phase in the panel.

The MOST current the neutral will have in a proper shared circuit is 20A. And that is if one of the circuits is pulling a full 20A, and the other 0A. Add current to the second and it starts to subtract off the 20A.

Look at the feed coming into your main breaker box. Two 120v legs capable of 200A each. With a single shared neutral for return. (which is allowed to be downsized a bit) cause the only way it would ever see 200a is if you were pulling a full 200A on one leg, and 0A on the other. Which is very unlikely to ever happen.

 

[grsthegreat]

If the neutral comes loose, how will there be a completed circuit at the outlet that his power tool is plugged into? He'll have a black 120 volt wire connected and no other wire connected. Seems to me he will have zero volts, not 220.

nope, he will have 220. Ive seen it happen more times than ican count. It has to do with losing the return path to source.

You would be amazed how bright a light buld can get...like a small sun

 

[KennyG]

If the neutral comes loose, how will there be a completed circuit at the outlet that his power tool is plugged into? He'll have a black 120 volt wire connected and no other wire connected. Seems to me he will have zero volts, not 220.

In the case of having no loads on one circuit and loads on the other, if the neutral is interrupted, you are correct. No voltage on the circuit. However, in the case of having loads on both circuits you will have 220 through both circuits because there will be a path between the two primary legs, which we all know is 220v. When I installed my common neutral circuits I knew about the failed neutral concern and accepted it as unlikely.

 

[LD1]

It all depends on where the neutral is lost at.

If its lost mid circuit somewhere, everything between it and the main box will still work normally. Everything upstream will have 220v.

IF lost at the main panel, everything is 220v

 

[SPYDERLK]

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?

You made it absolutely correct. That should help.

 

[SPYDERLK]

It all depends on where the neutral is lost at.

If its lost mid circuit somewhere, everything between it and the main box will still work normally. Everything upstream will have 220v.

IF lost at the main panel, everything is 220v

Yes. But it will always be some amount less than 220. The amt lower will be governed by the V drop across the operating loads on each side/phase. These loads are allowing crossover to the neutral beyond the break in the "upstream" part. ... There has to be an operating load to allow crossover. - - The only time yould see 220 is if one side had NO load. If both had loads the isolated neutral segment would carry any imbalance and the 220 would split proportional to value of the opposing loads'

If lost at the box, or even in the case of the later occurring break, you could not draw power from either leg alone. You would have to plug something in on each leg.