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My home has a relatively typical (in America) 100 amp 240v feed accomplished via three conductors - two 120v "hot" wires and one neutral. This gives me my 240v circuits (the two hots) and my 120v circuits (one of the hots plus the neutral).

Recently my neighbor severed two of those feeder wires while digging a trench. The two severed wires were one of the two hots and the neutral. Therefore, my home was only receiving one 120v hot wire and nothing else.

Doing an inventory of my home, I discovered the following:

  1. None of the dedicated 240v appliances worked at all (oven, HVAC, table saw, etc)
  2. Some of the standard 120v outlets and lights worked perfectly (and verified as stable with a multimeter)
  3. Some of the standard outlets and lights fluctuated with voltages ranging from 0v to 60v (rising and falling; not static).

My questions are:

  1. How did those 120v outlets work at all, much less perfectly, when there was no neutral? How was there any circuit with only one hot and no "return path"?

  2. Why did some of the 120v circuits exhibit a varying voltage between 0v and 60v? What could cause that?

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  • Because ground and neutral are bonded at the main panel, and apparently your ground is decent.
    – Tyson
    Feb 5, 2017 at 1:39

2 Answers 2

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It's using the earth as a return path

You really don't want to do that. Dirt doesn't conduct electricity very well.

Your neutral is bonded to ground in your main panel. The power company's transformer also bonds neutral to ground at the pole, and all your neighbors have neutral-ground bonds like yours. The current is trying to return to source (neutral) via your ground rod, wet dirt between your homes or the transformer pole, their ground rods, and back to neutral.

You're measuring it and saying your hot is varying 0-60 volts. No. Hot isn't damaged, so it's exactly where it belongs at 120V. Neutral has come UP to 60-120 volts! And ground has come with it! Because neutral is using your neutral-ground bond in the main panel, and lifting ground. Which means your neutrals and equipment grounding conductor is floating 60-120 V above actual proper earth. That's a good way to electrocute somebody because it means the grounded bodies of appliances or grounded equipment are also floating up to 60-120V!

Shut this off right now until it can be fixed.

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  • 2
    That makes sense. Yes, I treated it as dangerous and shut down all but the most critical circuits and then stayed out of the house until the power company came to fix the lines. That was less than an hour. Feb 5, 2017 at 5:03
  • @KurtGranroth The "most critical circuits" to shut off are ALL of them. Even if your heat pump is running on 120V and providing heat to the house, the metal casing for it is energized and anyone leaning up against it could be electrocuted. The only circuits that should have been left live were for life-support systems, and these should have been running on their own battery backup until the generator kicked in.
    – FreeMan
    Apr 11 at 11:52
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Some of the standard 120v outlets and lights worked perfectly (and verified as stable with a multimeter)

This suggests there was a path of at least reasonably low impedance connecting your ground/neutral system to the suppliers ground/neutral system. If you had an unsuually good grounding electrode system it's possible that this path went through the general mass of the earth, but I think it's more likely that it went through metallic pipework to another nearby property.

Some of the standard outlets and lights fluctuated with voltages ranging from 0v to 60v (rising and falling; not static).

I suspect this was caused by a 240V load cross-feeding from one hot line to the other.

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