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Thread: Dangerous Grounding?

  1. #1
    Join Date
    Dec 2018
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    3

    Default Dangerous Grounding?

    So we had a dryer fire, more on that later. landlord installed a new dryer and i received a shock off from it with the 30 amp break OFF, tested the breaker and it tested bad, replaced it. I used my volt meter between a near by 110 outlet for ground and the dryer cabinet while it was plugged in and the breaker OFF... i got a reading of 120 VOLTS!!!! i went thru and tested all my outlets and the polarity is switched. found one GFCI with a reading of 240 VOLTS between neutral and ground! I found a piggy back 15 amp breaker that when shut off the feedback stops. everything i can see in the box is wired correctly. we have currently moved out to stay with family until this dangerous situation is resolved. any ideas as to what is going on here?

  2. #2
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    248

    Default

    It sounds like you have an energized neutral. That should never happen unless the neutral between street/meter/panel is broken somewhere. Usually a loose/broken neutral will cause some voltage divide so instead of hot-neutral-hot being 120V-120V, it could be 180-60 or or 140-100. You'll see lights going dimmer and brighter when this happens (and that could burn up a dryer motor). Sounds like yours went full tilt to 240-0 which would require one leg to be completely shorted to neutral or one huge 120V load with just a light bulb on the other leg.

    This could happen at a subpanel (and mobile homes are subpanels). It is also possible some circuit is miswired and backfeeding things or someone tried to fix things after the neutral went loose and made things worse. With a loose neutral though, it will seem like anything turned on is putting voltage on the neutral so you need an experienced electrician to figure out the problem and fix this. Even if the neutral is grounded, it can still shock you in this fault case because most ground electrodes are poor conductors and wont trip a breaker at 120V.

    So the grounding could be fine, but the neutral most likely is not. Depending on how cheap the landlord is, once he says this is fixed I would use a meter on every outlet to make sure you have 120V from hot to neutral and hot to ground. The dryer should be 240V hot to hot, and 120V from each hot to ground and neutral (or just neutral if its a 3 prong plug). If everything seems OK, try it again at a few outlets after putting a heavy 120V load on one circuit (e.g. a cranked up space heater or hair dryer). Ideally, you want to measure a circuit on each leg of the service (typically adjacent breakers) to verify that both are near 120V to neutral with just one leg loaded. If you see 130V on one leg and 110V on another, that is probably OK, but about as far as I want to see things move. 120-120 or 122-118 is about perfect.

    Did you test the breaker when it was removed from the panel? If not, it was probably being backfed from some circuit that was on.
    Mark
    Kent, WA

  3. #3
    Join Date
    Dec 2018
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    3

    Default

    Thank you for your reply. I have an electrician coming in on Saturday. we haven't had any issues with lights going brighter or dimmer. I did not test the old 30 amp when i removed it from the panel box but like i said i did find a piggy back 15 amp breaker that when i turn that off my feedback problem goes away, so my guess would be that hot neutral would be on this circuit feeding back?

  4. #4
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    248

    Default

    Neutral can't normally become hot, as it is a short circuit path back to the transformer (if someone tied black to white, it should blow the circuit breaker). The only way the energized neutral can happen is if that neutral path is broken. Then, any load that is turned on will be going to the neutral bar which energizes all neutrals and possibly all grounded items (the green or bare wire). Most appliances aren't bare metal anymore, so shocking metal is hard to find. I would think your electrical panel chassis is live too (causing shocks) unless its a subpanel. In a subpanel, the neutral bar is isolated from the chassis, so only neutral wires will be energized and not grounds if the neutral between the main disconnect and the subpanel is broken. You'd tend to only notice shocks in this case on the old 120/240V appliances that have 3 prong plugs (stoves and dryers). But if you're fed from a subpanel, those circuits are supposed to use 4 prong plugs (but that was rarely done in the past -- very common wiring mistake). The 4 prong plugs are a mixed blessing -- you won't get a shock from the appliance chassis, but it can still burn up like yours did. The tingle usually give you the first clue that something is wrong before things go poof.
    Mark
    Kent, WA

  5. #5
    Join Date
    Dec 2018
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    3

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    Solved - Electrician found the neutral Buss was energized and was able to correct the issues. He found two switch loops that were incorrectly wired.

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