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I have a main breaker panel downstairs, and a subpanel upstairs. After I hired an electrician to rerun the service entry cables, nothing upstairs is right, and all the upstairs lights blew as soon as they were turned on.

Testing with a multimeter, I'm reading 240V from hot to neutral on all the outlets upstairs. I get the correct reading downstairs, 120V, so the problem seems to be the subpanel wiring.

I don't see any mistakes in the subpanel. Everything looks normal to me: no double-tapping; these are all single pole breakers; the neutrals and grounds are isolated from one another. What could be causing a single pole breaker to provide 240V? There must be something obvious I'm missing.

Here is the disconnect for the panel upstairs:

Disconnect for subpanel.

Here is the panel:

Subpanel, upstairs

Multimeter readings: hot to neutral: 240V. hot to ground, 120V.

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    Sounds like what should be neutral is instead attached to the other phase. The question is where.
    – keshlam
    Commented Sep 9, 2014 at 21:13
  • Photos are probably required.
    – Tester101
    Commented Sep 9, 2014 at 21:36
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    Floating neutral to the sub panel in the master shutoff breaker box... Connected to an insulated block connected to nothing else? Hmm.
    – Fiasco Labs
    Commented Sep 9, 2014 at 23:17
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    Another thing that looks very odd - but probably not a problem - is that the black / red feed colors are swapped going through the cutoff switch.
    – Michael Karas ♦
    Commented Sep 10, 2014 at 11:54
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    Normally, a qualified electrician would check their work before leaving [they'd probably pull permits, too] and if something turned out to be incorrect later, a qualified electrician would be back to fix it - improper installation is the sort of thing an electrician loses their license for. My advice is to bite the bullet and hire a licensed electrician to check out the installation. Improper electrical work is a severe life safety hazard. This is not something that should be debugged over the internet.
    – user23752
    Commented Sep 10, 2014 at 17:23

3 Answers 3

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I've labeled your image, to help you understand what's going on.

Labeled image

Off to the left, the grounding electrode conductor enters the box and terminates at the grounding bar. The feeder coming in the top of the disconnect has three wires, two ungrounded (hot) conductors, and a grounded (neutral) conductor. The two ungrounded (hot) conductors terminate at the disconnect, as they should. The grounded (neutral) conductor terminates at the grounding bar, as it should if this is where the service is grounded.

The feeder leaving the bottom of the panel has two ungrounded (hot) conductors, which terminate at the disconnect as expected. The grounding conductor terminates at the grounding bar, as it should. And the grounded (neutral) conductor terminates at the neutral bar. Unfortunately, since this appears to be where the service is grounded, the grounded (neutral) conductor from the lower feeder should be connected to the grounding bar.

As it's wired now, the grounded (neutral) from the lower feeder is connected to an isolated neutral bar. Which means that the grounded (neutral) conductor feeding the panel is floating, or not electrically connected to ground. Without a reference to ground, the voltage potential between either of the ungrounded (hot) conductors and the neutral can be anywhere between 0 - 240 volts.

Solution

Service grounding location

If the disconnect panel is where the service is grounded, you should move the white wire from the lower feeder to the grounding bar. Or you could bond the neutral bar to the grounding bar, using an appropriately sized conductor.

enter image description here
Click for larger image

Not service grounding location

If this is not where the service is grounded, you should move the bare conductor from the upper feeder to the neutral bar.

enter image description here
Click for larger image

Based on what you've said in comments; and because it's a 3 wire feeder and not a 4, it appears that this is where the service is grounded.

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Top picture, top wire (incoming supply):

  • Red - hot
  • Black - hot
  • Silver - neutral.
  • Copper - ground

Top picture, bottom wire (outgoing feed):

  • Red - hot
  • Black - hot
  • White - neutral
  • Silver - ground

The top picture has the supply neutral bonded to supply ground and feeder ground. It has the feeder neutral connected to nothing, so it appears - it connects to an insulated bonding bar with nothing else connected to it (the top left bonding bar in the top picture).

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  • To add, you MUST relocate the incoming neutral to the neutral bar (the one on the black plastic piece) and install the supplied bonding screw into that same bar. In fact, that ground bar in the main disconnect is not at all necessary. Who did this installation? I hope this guys was not a real electrician. I shutter to think what other mistakes there are that we cannot see.
    – Speedy Petey
    Commented Sep 9, 2014 at 23:09
  • Yes, this must be right. I had only traced this back to the disconnect earlier today, in order to take a picture, and that stood out to me. So, the neutral simply isn't connected to anything. I'll relocate it properly. Yes, this was a real electrician. He was positively awful, and charged me more than quoted, too. I won't be hiring him again. Thank you!
    – Jess
    Commented Sep 10, 2014 at 3:12
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Call back the "electrician" because if you try to fix it he probably never will. If the electrician won't come back call the licensing bureau.

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