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Thread: Absolutely Shocking Garage Door Opener Question

  1. #1
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    Absolutely Shocking Garage Door Opener Question

    To keep a long, shocking story short, I just got zapped by touching the steel bracket holding our garage door opener and the top of my DC. Further investigation shows that the DC is properly grounded, and the voltage is live between the garage door opener and any ground, such as an exposed steel conduit. Obviously, this is not a good thing. It stings.

    The garage door opener is plugged into a 3-prong outlet. My first step will be to verify that outlet is actually grounded. What else do I need to be looking for?
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
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  2. #2
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    OK, I did a bit more digging. Here's what I've got figured out so far...

    I have an old circuit in the garage that was in place when we bought the house. I also have new circuits that were added a couple of years ago. The garage door opener was plugged into the old circuit. If I put a meter between the ground leg of the old circuit and touch the other lead to a known good ground (the conduit on my new circuit), I get 70v AC. My meter also reads 70v AC when I check the hot and common leads on the circuit. Since that's supposed to be 110v or so, I suspect it's time for new batteries in the voltmeter.

    Funky meter readings aside...on the old circuit, I'm reading 70v between the hot leg (narrower slot on the outlet) and the ground leg, and I'm getting about half that voltage between the common leg and the ground leg.

    On the new circuit, I'm getting 70v between the hot leg and the ground, and no voltage between the common and the ground. I'm assuming my new circuit is OK. Although I installed the outlets, the wiring was run by the electricians. They checked all my work with a meter and found no issues.

    So...any ideas what's up with my old circuit? Why am I getting partial voltage between the common and the ground legs? Why am I getting full voltage between the ground of the old circuit and the ground of the new circuit? I suspect they're related, and although I know wiring basics, I'm not real experienced in troubleshooting AC voltage.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
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  3. #3
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    The ground and neutral are usually bonded together at the distribution panel and that seems to be the case for your new circuit. Sounds like the old circuit may have a broken or missing ground connection and the GDO has a short. Does the GDO work normally? As for the 70V, maybe your electric company is giving out IOUs for the other 40V .

  4. #4
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    Quote Originally Posted by Charlie Schultz View Post
    The ground and neutral are usually bonded together at the distribution panel and that seems to be the case for your new circuit. Sounds like the old circuit may have a broken or missing ground connection and the GDO has a short. Does the GDO work normally? As for the 70V, maybe your electric company is giving out IOUs for the other 40V .
    Sounds more to me like the GDO has an open neutral, and the ground wire is what's completing the circuit. Likely a broken wire within the GDO, or a loose wire at the outlet.
    Jim D.
    Adapt, Improvise, Overcome!

  5. #5
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    Thanks, guys. The garage door opener works fine, and when it's on the new circuit, the meter behaves normally. I'll kill the power to the old circuit later today and start pulling outlet covers to see if I can spot anything loose. I'll also check to see if the old circuit is actually grounded, or if it's really just a 2-wire circuit with 3-hole outlets.

    I tried a new battery in the meter, and it's still reading 70 volts. It's a 25+ year old Radio Shack meter, so I figured it was time get something newer. I've been wanting an auto-ranging meter, so I just ordered one of these:

    Equus Auto-Ranging Meter
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
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  6. #6
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    I'm no electrician, but...
    Have you opened the outlet box for the GDO to see if the hot and neutral (right word?) are connected correctly? Seems to me someone could have accidentally reversed the wires when it was installed.
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  7. #7
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    With my expertise in things electrical, the way I go about resolving problems like that is to.....pick up the telephone and call an expert.

  8. #8
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    No other advice to offer, but at midnight I'm sure it was better than morning coffee for waking you up, looks like it kept you up another two hours in fact.

    Does sound like a loose or broken neutral though.

    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  9. #9
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    I want to know if you took a picture of your hairdo after the shock...

    Hope you figure it out and it's a quick fix!
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  10. #10
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    Keep in mind that the problem could be anywhere in that particular circuit. With the breaker off, do you still get the same readings? or are all the wires dead? Jim.
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