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Thread: The Hunt for Objectionable Voltage

  1. #1
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    The Hunt for Objectionable Voltage

    Subtitle: This is why homeowners should not do electrical work.


    I was called out to a home where an outside ceiling fan was giving a shock. The leakage was very slight. I could not feel it but the HO who was barefoot and standing on damp concrete said it was tingling. A voltage reading between the fan chain and a nearby receptacle ground read 120 volts.

    This place was a mess electrically. I'll give you the highlights. There was a main switch, an outside four slot A/C panel, two inside 100 amp house panels, and a pool panel. Only the pool panel had grounds and neutral separated. The A/C panel was not bonded and had exposed conductors as the insulation had cracked and fell off in places. A voltage reading between the case and a hot read zero.

    Now it gets interesting. I flip off all the house and pool panel breakers but the fan keeps running. The fan cable traces back to an outside J-box about six feet away. Opening the J-box reveals eight 15 and 20 amp circuits all connected to the 50 amp feeders for the air handler. No over current protection. AND .... all the neutrals and grounds are tied together.

    I assume separating the grounds and neutrals would have solved the objectionable voltage problem, but I didn't do that. Instead I explained the fire danger and then disconnected most of the circuits from the 50 amp feeder. (The HO would not let me disconnect the circuit powering his TV.) I then sold him a job to install a subpanel at that location to make things safe. Apparently, this wiring had been there twenty or so years and was not overloading the 50 amp breaker powering the air handler. We are in discussions about repairing the rest of the electrical mess.

    What I find interesting about this is the objectionable voltage "backed up" to the fan instead of flowing back to the panel (source). I guess it was seeking all paths to ground and my barefooted client provided one. What is strange is that the objectionable voltage was never noticed until now (20 years later). Not sure if anything changed.

  2. #2
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    Upon re-reading my post I realize the correct term is "objectionable current".

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    did you try a low z, wiggy, or other solenoid tester for voltage. if you were measuring neutral to ground you shouldn't have got 120v, there was a ground fault if so and the fan wasn't bonded to an egc that's tied to the xfmr x0. think about it, neutral is after the load and connected to EGC. the fan had a ungrounded 120v (120v to neutral/ground) conductor shorted to it. go measure the voltage in a receptacle from neutral to ground, even with something running off the other receptacle of a duplex receptacle. if the neutral was double bonded you would have a parallel path for current, but 120v is a circuit with no load (short/ ground fault), it shouldn't be close to 120v for a 120/240v system, perhaps you used a high z meter and didn't get a good reading but it sounds like a ground fault to a fixture that's not bonded to the system egc.
    Last edited by Wire-Smith; 07-10-18 at 12:49 PM.

  4. #4
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    Quote Originally Posted by Wire-Smith View Post
    did you try a low z, wiggy, or other solenoid tester for voltage. if you were measuring neutral to ground you shouldn't have got 120v, there was a ground fault if so and the fan wasn't bonded to an egc that's tied to the xfmr x0. think about it, neutral is after the load and connected to EGC. the fan had a ungrounded 120v (120v to neutral/ground) conductor shorted to it. go measure the voltage in a receptacle from neutral to ground, even with something running off the other receptacle of a duplex receptacle. if the neutral was double bonded you would have a parallel path for current, but 120v is a circuit with no load (short/ ground fault), it shouldn't be close to 120v for a 120/240v system, perhaps you used a high z meter and didn't get a good reading but it sounds like a ground fault to a fixture that's not bonded to the system egc.
    So I installed the subpanel I mentioned above and separated all the circuits, neutrals, grounds so everything was correct. Then I tested the fan again. I touched the fob on the pull chain and didn't feel anything. I put my meter on it and read 120v to a nearby receptacle ground. The homeowner's son grabbed the fob barefoot and got hit hard (ripping the fob off the chain.) He says to me "don't tell anybody I did that." I said "it will be our little secret."

    I won't be doing any more troubleshooting on this project so I won't know the exact source of the problem. It either the fan itself or a j-box between the fan and the new subpanel. The HO has decided he's paid me enough and he can take it from here. (He's braver than most.)

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    Quote Originally Posted by Coppersmith View Post
    So I installed the subpanel I mentioned above and separated all the circuits, neutrals, grounds so everything was correct. Then I tested the fan again. I touched the fob on the pull chain and didn't feel anything. I put my meter on it and read 120v to a nearby receptacle ground. The homeowner's son grabbed the fob barefoot and got hit hard (ripping the fob off the chain.) He says to me "don't tell anybody I did that." I said "it will be our little secret."

    I won't be doing any more troubleshooting on this project so I won't know the exact source of the problem. It either the fan itself or a j-box between the fan and the new subpanel. The HO has decided he's paid me enough and he can take it from here. (He's braver than most.)
    too bad, you'll have that. at least you fixed a big part of the mess.

    do you understand what i'm saying about it's very unlikely to be from a double bonded neutral? that i'm quite sure it's a ground fault and the fixture is not properly grounded? getting hit that hard reassures me that it in fact is truly 120v and a low resistance fault, not from double bonding

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    Quote Originally Posted by Wire-Smith View Post
    too bad, you'll have that. at least you fixed a big part of the mess.

    do you understand what i'm saying about it's very unlikely to be from a double bonded neutral? that i'm quite sure it's a ground fault and the fixture is not properly grounded? getting hit that hard reassures me that it in fact is truly 120v and a low resistance fault, not from double bonding
    I agree the fan probably isn't grounded. The fact that I could not feel any current means the current flow was very low. I've gotten hit many times wearing sneakers and work boots. I don't think I was that isolated. I still suspect grounds and neutrals tied together possibly in the fan itself.

  7. #7
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    but also the voltage is not from double bonded neutrals, when measuring neutral to ground your not going to get 120v on a 120/240 system. not only is the load in series with what your measuring, so voltage will drop across it (you will be measuring lower voltage) but also the neutral is likely tied to ground (sounds like in your case in extra locations). what your effectively measuring is an ungrounded circuit conductor to ground. an ungrounded circuit conductor is connected to the fixture housing.

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