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Thread: open neutral/s

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    open neutral/s

    At a 240 volt residence service with aluminum branch wire with black cable jacket through out entire home. I received a call that had open neutral in two different circuits. When I opened an outlet tested a duplex, phase to neutral 15 volts, Phase to ground 120 volts neutral to ground 240 volts! I then tested phases in service 130 volts to neutral, when neutral was connected to ground in duplex service phase reading 120 volts to neutral. When I connect neutral to ground at duplex and tested phase to neutral 120 volts. I then opened outlets in several rooms and could not find a loose or broken neutral wire. There was some renovation years ago.I have no access to attic. I could use someone give me some insight how to locate open neutral or cross phased wires.? This seems to be a hazardous situation.

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    Quote Originally Posted by Adams14 View Post
    At a 240 volt residence service with aluminum branch wire with black cable jacket through out entire home. I received a call that had open neutral in two different circuits. When I opened an outlet tested a duplex, phase to neutral 15 volts, Phase to ground 120 volts neutral to ground 240 volts! I then tested phases in service 130 volts to neutral, when neutral was connected to ground in duplex service phase reading 120 volts to neutral. When I connect neutral to ground at duplex and tested phase to neutral 120 volts. I then opened outlets in several rooms and could not find a loose or broken neutral wire. There was some renovation years ago.I have no access to attic. I could use someone give me some insight how to locate open neutral or cross phased wires.? This seems to be a hazardous situation.
    Start at the Service entrance. Check line to line voltage. Check each line to neutral voltage. Record them. If you have 240 L-L you should have close to 120 on each L-N. Yes? your good there. No? look at the incoming neutral connections from the panel on out to the utility.

    While your there look at each connection on the neutral bar and each connection on the CBs.

    Determine which CBs are giving you grief. Are they a MWBC? Find the neutral(s).

    Shut the circuits off. Remove each and every device. Are they back stabbed? Drop the affected fixtures, if any.

    Aluminum branch circuit wiring will be fun.

    Take a hair dryer with you to load up the circuits.
    Tom
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    Many times on aluminum you can put your hand on the opening and feel the hot device, pull it out and find the neut. burned back.

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    Quote Originally Posted by ptonsparky View Post
    Start at the Service entrance. Check line to line voltage. Check each line to neutral voltage. Record them. If you have 240 L-L you should have close to 120 on each L-N. Yes? your good there. No? look at the incoming neutral connections from the panel on out to the utility.

    While your there look at each connection on the neutral bar and each connection on the CBs.

    Determine which CBs are giving you grief. Are they a MWBC? Find the neutral(s).

    Shut the circuits off. Remove each and every device. Are they back stabbed? Drop the affected fixtures, if any.

    Aluminum branch circuit wiring will be fun.

    Take a hair dryer with you to load up the circuits.
    Is there also a cross phase because I measured 230 volts between neutral and ground

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    Quote Originally Posted by Adams14 View Post
    Is there also a cross phase because I measured 230 volts between neutral and ground
    Your voltage and or description of how you took them did not make sense to me. Not that you werent on the right path, I couldn’t sort out what you did. A loose or missing neutral can result in a line to neutral voltage being close to expected L-L while the other L-N will be low. The two L-N voltage checks should equal the L-L voltage. 30+210=240. A high neutral to EG voltage would be another indicator of a bad neutral depending on where in the circuit you have your meter leads.

    Use the hair dryer to add load. Cycling it will cause voltage swings on L-N readings. A bad neutral at the service panel or before will affect voltages throughout the home. A MWBC with a missing or compromised neutral will give the same voltage patterns, but will affect only those of the MWBC.
    Last edited by ptonsparky; 01-23-19 at 07:25 AM.
    Tom
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    Neutral issues are a frequent topic. Use the search function to look up previous threads.
    Tom
    TBLO

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    If only 2 circuits are affected my guess is you have a multiwire branch circuit that has a bad connection somewhere. Turn off the circuits and see what recptacles, switches etc are on the circuit.

    Turn the circuit back on and see what parts of the circuit are affected. If the entire circuit is affected then check the neutral in the panel. Otherwise find the closest outlets to the panel and start from the outlet that is not affected- just before the affected ones.
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  8. #8
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    Quote Originally Posted by Dennis Alwon View Post
    If only 2 circuits are affected my guess is you have a multiwire branch circuit that has a bad connection somewhere. Turn off the circuits and see what recptacles, switches etc are on the circuit.

    Turn the circuit back on and see what parts of the circuit are affected. If the entire circuit is affected then check the neutral in the panel. Otherwise find the closest outlets to the panel and start from the outlet that is not affected- just before the affected ones.
    Most likely.
    Tom
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    If things were connected properly to begin with and all that has failed is a neutral connection, you shouldn't get a neutral to ground voltage over ~120 volts. There has to be more than just a failed neutral going on here, and both L1 and L2 are supplying power to the failed component(s) in some way to be able to read over 120 volts N-G.
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  10. #10
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    Quote Originally Posted by kwired View Post
    If things were connected properly to begin with and all that has failed is a neutral connection, you shouldn't get a neutral to ground voltage over ~120 volts. There has to be more than just a failed neutral going on here, and both L1 and L2 are supplying power to the failed component(s) in some way to be able to read over 120 volts N-G.
    Wouldn't you get an open circuit voltage from failed neutral to EG? Yes, 120v unless the neutral is compromised at the service or before.

    Part of the reason those taking voltage readings have to be very specific as to what they are doing and where they have the probes. I know what I mean when I take a reading to ground, but do you know what I think I mean?
    Last edited by ptonsparky; 01-23-19 at 08:21 AM.
    Tom
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