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I have a weird one - electricians with 20+ experience haven't heard of this one so I am hoping you all can help me!

I have a small condo which appears to run on at least 2 main circuits. When all of the lights are on, they will run for an entire day and then later in the eve the lights will flicker and the power will go out on one half of the condo. They will stay out for about 3 hours and then come back on. The breaker does not trip. In addition to that - the refrigerator and oven will also go out and start back up with the lights.

Here's the weird part - if I put the AC on - the entire system will "reboot" and work fine again. The AC breaker is located directly above the other circuit breaker which is tied to the circuit which keep going out.

Also - these are MC wires - some are into plastic boxes and have the ground wire wrapped an inch or two up the outside of the MC cable.

Your advise is great appreciated

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    Do you shower in the mornings? Do you have an electric water heater? Is the Air Conditioner a 240V unit with a 240V breaker? It matters. If half the condo is out, does turning on a 240V electric appliance like range or dryer make the wayward circuits return? Do those appliances work properly? May 29, 2023 at 5:10
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    I'm not an American, but this smells like weirdness with the two 120V hots, and the 240V AC is somehow bridging things back to normal. Perhaps not a full "lost neutral" but a very confused and disoriented neutral ? Harper will doubtless have an answer soon.
    – Criggie
    May 29, 2023 at 11:41
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    @Criggie I'm smelling a lost hot wire, and turning on a 240V load is connecting the dead hot wire to a live one (via the resistance of the load). It's sorta like if your neighbor had all 3 phases with a single-phase 400V water heater between L1 and L2. L1 was completely broken at the street transformer, but everytime their water heater came on, your house on L1 would be connected to L2 via the resistance element in the water heater. That would make the water heater very, very slow to heat since it's in series with the L1 houses. But when it reached temp, it would click off, and... May 29, 2023 at 22:18
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    ...all the L1 houses would lose power as mysteriously as they gained it. Add a pattern of "taking showers in the morning" and it's starting to look like OP's scenario. May 29, 2023 at 22:20
  • Thank you for the responses - No - we do not have an electric hot water heater. The range and refrigerator also go out when the lights go out. The only thing that resets the system is if I put the AC on. Then it comes back on immediately. Otherwise it takes about 3 hours. Yes the AC is on a 240V breaker.
    – Sean
    May 30, 2023 at 12:09

1 Answer 1

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This is assuming that you are in North America and have 240/120 or 208/120 volt split leg service.

It sounds like you have a loose hot entering your panel. This kills the 120 volt leg feeding the lights. When you try to turn on the 240/208 volt air conditioning, it acts as a conductor connecting the good hot to bad.

You need an electrician to check this out ASAP, and not the one with “20+ years” who hasn’t heard of this!

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    Yes - I am in the USA. Thank you for all of the helpful comments! Appreciate it!
    – Sean
    May 29, 2023 at 17:17

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