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With the light switch off, I can touch the neutral and line, or ground and line or neutral and ground and not feel anything, no shock.

But if the two neutrals or neutral and ground touch/rub, they cause a static electricity type of spark.

What would be the cause of this and would this be why my bulbs constantly go out.

I’m getting 4.2v between the line and neutral/ground with the switch off. Can’t feel it when touching both.

The neutral also goes to another light which is fed power by a third red, hot wire.enter image description here

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    I am seriously concerned that you are checking things by touch when you know there may be something wrong with ~ 120V wiring. BE CAREFUL – manassehkatz Aug 22 '18 at 2:03
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    Welcome to StackExchange. All due respect, STOP USING YOURSELF AS A TEST INSTRUMENT. RIGHT NOW. And don't do it again! The peculiar environmental conditions which prevented you from being killed are not reliable and cannot be counted on. If you want to touch wires and use your body to detect voltage, they make 1-wire voltage testers for that. They're basically what you're doing, except the neon light inside limits them to safe currents. – Harper Aug 22 '18 at 2:46
  • I turned the switch off, taped it so it couldn’t be flipped. While I’ll often test with a multi-meter, a quick pat with the tips of the fingers has historically been enough to verify no voltage. I was surprised to find 4 volts as I did, not sure at which point it becomes detectable by touch. – Number4 Aug 22 '18 at 2:47
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    All due respect, I wouldn't even do that with the breaker off. I "verify off" by flashing hot to ground. One time I did that, the whole circuit lit up again! When I subsequently flashed neutral to ground, I got a blinding arc flash! Remember you are working on circuits that are broken. As for the "pat of the fingers" test, ask anyone who works from an insulated line truck on live wires, which I do. Live wires feel like nothing. Seriously. Your test doesn't work. – Harper Aug 22 '18 at 2:54
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You keep saying "neutral and ground". A common mistake is to believe they are the same thing -- after all, they're tied together back in the main panel, that's the same as tying them everywhere, right? Nope.

Neutral is a working conductor: it is a normal current return path. It "works for a living". It's subject to voltage drop, for instance. It must be tightly paired with the "hot" conductors so the wires' magnetic fields cancel each other out.

Equipment Ground is an emergency safety shield. Normal current must never flow over it! Any current on ground is fault current and we certainly hope that is caught soon.

The purpose of the tie back at the main panel is equipotential bonding. The bond could be a car battery (intentional 12VDC bias between N and G); or a 2V transformer (2VAC offset between N and G) -- who cares -- the point is to bond neutral to be near earth, and thus keep hots within around 120/230V of earth - otherwise they could float/rattle at high voltages and be much more lethal.


So why the sparks?

Between the two neutrals, it's because there are downline loads being served by that neutral. When you sever a neutral, you cut off current flow, and the downline load "lifts" the neutral wire to 120V. Now you have 120V across those two neutrals. When you touch them together again, you complete the circuit and the downline load comes back on again. The spark is small because it's current-limited by what the downline load will draw.

Between neutral and ground, it's because you have paralleled neutral and ground. when you parallel 2 wires (don't), current flows in proportion to their conductivity. The conductivity of neutral and ground are pretty close, so when you do that (don't), about half the current flows via ground instead of neutral. Again the downline load limits current, so the spark stays small.

Why is neutral and ground not precisely the same voltage? Because neutral is workin' for a living, and ground is not. You're seeing voltage drop on the neutral, which since a neutral starts at 0V, tends to lift the neutral's voltage up a volt or two. It's the same effect as a beam-style torque wrench: the heavy beam bends with the many foot-pounds of torque, but the indicator beam is under no strain, so remains straight. The difference indicates torque.

If you knew the exact resistance of the neutral wire, you could compute current using that observed ground-neutral voltage difference "E", and known neutral resistance "R", plug them into E=IR and out pops I, your amps.

Oh yeah... your bulbs

Your problem is completely unrelated to this garden walk through the world of neutrals and bonding. The readings you're asking about were a red herring, sorry. Since you have a DVM, measure voltages on circuits in your house which work - as many as possible - and look for anything weird, especially some below 120V with others equally above 120V.

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This is caused by the difference in potential between the ground wire and the neutral circuit. All conductors have resistance. This resistance causes voltage drop across the line when current flows through it, such as when you have the lights on. I won't go into detail here since this isn't really meant to be a forum to discuss electrical theory

Most importantly, as others have commented this is normal and you should insulate the neutral wire by placing a wire nut over it. The neutral or hot in a circuit should never be exposed or connected to any metal chassis except at the load center (most people call it a breaker panel). Also, there is little reason to handle the conductors of a live circuit.

If you want to learn more about voltage drop this is a good starting point:

https://en.wikipedia.org/wiki/Voltage_drop

  • I find it interesting, because I’ve never encountered this “static electricity” sparking between neutrals or neutral/grounds in the 10+ years I’ve been doing electrical work. That I can remember.... – Number4 Aug 22 '18 at 2:51
  • Correction: they should only be connected at the main load center/breaker panel -- subpanels do not bond neutral and ground – ThreePhaseEel Aug 22 '18 at 3:06

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