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enter image description hereenter image description hereI just got back from visiting the house I am moving into in two weeks. I was checking out the electrical circuits in the garage to see how I will be able to run my woodworking tools. I did not get around to checking the amperage on the circuits because the simple test for live receptacles gave voltages that threw me. There is a circuit for a Room AC with the proper outlet that reads 240 volts as it should.

The circuit over the counter over existing cabinets along one wall has two 120 v receptacles in separate boxes. When I probe the outlets I GET 240 VOLTS. There is a separate circuit with only one 120v receptacle on the back wall. It must be on a separate circuit because on it I get 40 TO 50 VOLT READINGS. Any body have any idea about what kind of jackass wiring would cause this ?

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    240V on 120V receptacles could be a sign of a big problem, or it could be a deliberate miswiring for the previous owner's tools - so either part of a big mess or possibly a really easy fix at the breaker. 40V - 50V could be phantom voltage from a partially disconnected circuit or it could be a sign of a really big problem. a) How are the circuits in the house? b) Can you upload a picture of the main panel and any subpanels? Feb 2, 2021 at 20:00
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    @manassehkatz-Moving2Codidact Agreed: the previous owner may have had a tool that needed (or converted) to 240v and didn't want to bother with changing the plug/outlet to the proper NEMA components. Dangerous and stupid, IMHO if that was the case. If the OP could pull out the outlets (WITH THE POWER OFF) as well as the cover of the main panel, take some pics, that would be helpful. Feb 2, 2021 at 20:05
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    Yes, pictures of all relevant panels, ideally with the deadfronts removed, would be very helpful. Pictures looking into the outlet boxes may also be needed.
    – Nate S.
    Feb 2, 2021 at 20:36
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    It wouldn't be a bad idea to check voltages in all the house receptacles while you're there, to see if the problem only affects the garage or exists in the house as well.
    – Mark
    Feb 2, 2021 at 21:16
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    Where does the white wire coming out of the bench outlet pipe end up going? It disappears behind some stuff, and then I can't track it. Theoretically it should be on the neutral bar, but if it goes to a breaker, that explains your 240V.
    – Nate S.
    Feb 4, 2021 at 0:23

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I suspect you have a loose (or open) neutral on a 3-wire circuit. That is to say, 2 hots sharing one neutral. Going forward I am referring to these 2 hots as A & B. The 2 hots are on opposing legs of the panel, hence 240 volts. The neutral becomes open somewhere before returning home to the main neutral bussing.

Your 240 volt problem outlet is on circuit A. Somewhere on circuit B you have a lightbulb turned on (not illuminated due to loose neutral) that is feeding the 120 volts from B leg through the lightbulb and back onto the neutral.

Because this 3-wire circuit shares a neutral, AND the neutral is open prior to returning home to the neutral bussing, that neutral wire on your problem outlet is reading 120 volts to ground. Since this 120 volts to ground is from B leg of the 3-wire circuit you have created the scenario you have described.

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