Electric question - hot neutral

[Tony]

I have an overhead light fixture that was failing intermittantly. I opened the J box of the on/off wall switch controlling that overhead fixture . I have a twisted bundle of 4 white wires stuffed into a wire nut. The white neutral for the overhead light had loosened from the group. When I tried to reattach it properly to the other three twisted together, tiny sparks flew. One of the neutral wires is hot. I isolated and disconnected this neutral, and reconnected the 3 other neutral feeds. Everything upline from there now works.

I get a reading of 120v when I attach a voltmeter to the hot white wire and ground it to the box. When I short the wire against the metal box, BIG sparks fly.

I don't want to connect it to the other white wires again

The disconnected wire is to the floor outlets in one room.

Prior to my disconnecting this wire the floor outlets worked. (Last time someone worked on electric in this room was over 7 years ago)

What would cause this wire to be hot, yet still appear to function? If I had an incorrectly polarized outlet, wouldn't it short out against the ground?

Am I missing something Any ideas?

Thanks,

Tony D

[DanG]

One of the uses on that circuit has the wires on the wrong screws. Color on brass, white on silver.

If they are all receptacles, get one of these to check polarity and ground:

[Charles]

Is there any voltage between the white neutral wires and the green (or bare) ground wiring? There should be none. If there is, investigate that first. Your neutral is not attached to the safety ground.

Verify that the outlets don't work now that they are disconnected. If they still work, you have another problem.

Perhaps some one confused black and white. Have you disconnected the black wire going to those floor outlets?

Draw the existing wiring diagram. A picture may help you sort it out.

[Dave]

The white wire is a return path for hot to earth ground. If something on one of those outlets downstairs is actively used, all what you see it normal. Unplug all appliances et all downstairs outlets, try it again. Dave

[Tony]

Thanks for the replies. Dave seems to have hit on the proper solution for my particular problem. I thought I had unpugged or shut off everything prior to my original tests. I Missed a computer monitor and a clock. With thhem removed - No more voltage. no more sparks. I'll rewire it all in daylight tomorrow.

Thanks all.

Tony ===========

[Wayne Whitney]

Why would he see 120V between the neutral and ground then?

Wayne

[Robert Allison]

Because it is the return path for the circuit, the neutral is, in essence, the hot. So just like finding current between your black wire and the ground, you find current between the neutral and the ground.

Unplug the device that is providing the circuit continuity and the phenomenae goes away.

[Wayne Whitney]

[Sorry if this is a duplicate.]

Sure, there will be current on the neutral, equal to the current on the hot for a 120V circuit. But the load will cause a voltage drop of almost 120V, so while the hot will be 120V from ground, the neutral should only be millivolts above ground. I think that if the OP truly measured 120V between a neutral and a ground, just having a device plugged in downstream doesn't explain that.

Maybe what was happening was that with the downstream neutral disconnected (no circuit), the voltmeter was giving a phantom 120V reading due to the induced current from the parallel hot conductor. As a separate matter, touching the downstream neutral to the grounded box, while a downstream load was plugged in, completed the circuit for that load, causing the spark.

Cheers, Wayne

[Dave]

[Dave]

No.

Any residential circuit on which has power drawn from the hot needs a neutral. The neutral carries the current to earth ground. The difference/potential in those conditions is the neutral will be at a potential equivalent to the difference voltage drop of the the load and the actual supply voltage AND earth ground. Thus, the neutral is hot minus the load vs. earth ground is the actual potential.

The voltage drop is negligible. The current draw may be more perceptible, but not measured in this case.

A voltage drop to zero across a load is effectively infinity impedance. No current can occur in such condiitions. No current means no electrical flow. Wouldn't warm your tongue, never mind a spectacular electrical air arc. What's present on one part of the circuit on the same wiring is also present down the line. Dave

[Wayne Whitney]

Actually, it returns it to the source, the power company transformer--the earth ground is relevant only because the local transformer is center tapped and earthed.

Not sure what you are saying here. If the circuit consists of Hot Transformer terminal -> Hot wires -> Load -> Neutral wires -> Grounded Transformer terminal, then the voltages above ground at each point might be 120V (Transformer), 119V (Hot wire at the Load), 1V (Neutral wire at the Load), 0V (Grounded Transformer terminal). Under normal operation, there will never be a 120V voltage difference between a neutral and an earth (ground).

As for the spark, it indicates current flow and was probably just due to completing the circuit by connecting the neutral to the EGC, which is bonded to the grounded service conductor at the main disconnect.

Cheers, Wayne

[Erik Dillenkofer]

[Wayne Whitney]

Ah, of course, thanks for the explanation! Sorry to have been a bit slow on the uptake here. When there is no circuit, there is no current, so there is no voltage drop across the load, so the measured voltage on the open neutral is 120V.

Thanks, Wayne

[Dave]

Begging your pardon here. Two phases of voltage normally enter a home at the entrance panel. One phase is strictly used for 115/120 VAC to outlets, lighting and such.

Earth ground is introduced at the end of the utility providers entry to the users panel. It can be one panel located near the utility pole or outside the house or a panel inside of the house. Depending where this specific panel is, determines the function of earth ground at that point. There is no physical tie to any of the utility regarding earth ground and the users earth ground.

The users panel where the 115/120 VAC is introduced is where neutral is tied to earth ground. Neutral goes nowhere else on the return path.

Voltage potential measuring is assuming there is an open between the 2 points measured. IE - hot and neutral. When measuring between the hot and neutral across a load, that measures the difference accounting for the load. If that load exists, and a spark gap is made between the neutral and earth ground, the remaining voltage potential jumps the gap to earth ground. Creating a spark.

A simple DC battery and light bulb (load) is a good graphical representation of the same thing. The negative side is hot. The positive side is earth ground. The wire from the light bulb to the positive side is neutral. The only difference is that current does not fluctuate and change directions in a DC circuit, and voltage potential doesn't change @ 120Hz..

Dave

[Wayne Whitney]

Dave, I think we are in agreement. I was missing the fact that with an interrupted neutral, there is no current flowing in the circuit, so there is no voltage drop across the load, so the load end of the interrupted neutral is at the same voltage as the hot.

Cheers, Wayne