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Thread: Whole House Lights Dimming

  1. #1

    Default Whole House Lights Dimming

    I am having a problem with the lights my whole house dimming, seems to be when there is a load on the electric (AC on a hot day etc.) but also happens when there is not much of a load. The lights dim every 1 or 2 minutes for 2 seconds exactly.

    Had the utility company out 4 times (they were here today again), everything checked out OK outside and no issues. Had 3 electricians check inside and all said could not find anything. I am stumped.

    Today I checked with a multi tester and here is my results. Voltage at outlets start out at 120.4 and slowly over time (10-15 mins) goes to 117.4 with A/C running, I see downward spikes to 115.2 and then back up to 117 when the dimming happens.

    What do I do? Getting tired of hunting this down.

    I really appreciate any help.

  2. #2
    Electrician ActionDave's Avatar
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    It is the result of your A/C unit kicking on. It is normal and not much can be done about it. Converting to fluorescent light bulbs will reduce the dimming so it won't be as noticeable.

  3. #3
    DIY Senior Member Hairyhosebib's Avatar
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    If you live in the country and have your own transformer on a pole, it might be the transformer. My brother in law had built a new home in the country. A new transformer was placed on a pole to feed his new home. A few months later it started feeding half the voltage to his home that was supposed to be fed into the panel, it screwed up a lot of appliances. The power company tried to feed him a line of BS but they did not know that he built power transformers by hand for a company called Kirby Risk in Lafayette, IN. He pretty much already knew what the problem was. This was in the early 90's.

  4. #4
    In the trades Dana's Avatar
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    Unless you're on your own transformer, he fact that the voltage dips are periodic and with exactly the same duration indicates there is probably some heavy load on your local grid branch that is cycling. It feels something like an AC compressor attempting to start, failing to get enough torque to spin-up, causing a reset time-out before attempting again.

    While it affects you (and everyone else on your side of the transformer), as long as your line voltage is within range it's not necessarily going to be the utility's problem to fix.

  5. #5
    DIY Junior Member 4bsydow's Avatar
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    You might check each phase to ground at your panel. There is a possibility you have a loose neutral , 1 phase will be much higher than the other if your neutral is loose or going bad.

  6. #6
    In the trades Dana's Avatar
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    While the loose neutral issue might cause dimming, it wouldn't have the regular periodicity and duty-cycle problem unless that intermittent load was on one (and only one) of the phases, and inside his house. Loose neutrals sometimes show up as flicker when there is a single-phase motor with a regularly varying load (like a top-loading washer running it's agitator, etc.). But with the symptom being a precise 2-second dimming period every few minutes (and only during air conditioning loads), a loose neutral wouldn't be a prime suspect.

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