How to figure out six wires and which goes with which?

Discussion in 'Electrical Forum discussion & Blog' started by Homeownerinburb, May 14, 2013.

  1. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    I'm going to be replacing an old surface mounted 100amp combination panel that replaced a much older panel many years ago.

    The owner tells me that the house is wired with cloth and rubber, but all the wire in the panel looks to be at least tw or possibly even thhn.

    Now that the code demands that we tie the handles of circuits that share a neutral, I am scratching my head. In two places circuits leave the panel with four hots and two neutrals.

    I don't have the first clue as how to figure which are the hots that go with the particular neutral.
  2. leejosepho

    leejosepho DIY scratch-pad engineer

    So, you have 8 hots and 4 neutrals to sort out?

    I would first number the hots, then turn them all off and turn them back on one-at-a-time to figure out where each one goes and get that all written down. For example:
    1) bathroom light
    2) bedroom #1 outlets
    etc.

    After that, I would turn them all off once again and disconnect all hots and neutrals to be checked and matched. At that point, I would check all the loose wires to be sure no stray voltage is coming back through any of them, and then I would begin checking for continuity to see which hots are related the which neutrals.

    If you are not absolutely certain of being able to do all of that in complete safety, hire an electrician who can.
  3. ActionDave

    ActionDave Electrician

    Messages:
    345
    Location:
    Colorado
    Good answer leejosepho. One must be careful there are no cross neurtal contamination. To check for that you would use an amp-meter while the circuits are energized.
  4. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    One of the jobs that clips over the wire, a non-contact?
  5. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    Label all the wires so that I can put it back together the way it started.....

    Disconnect everything.

    Leave all the lights in the house on (to ensure a path from the hot to the neutral).

    And look for continuity?

    I should also find continuity between the hots sharing a neutral, yes?
  6. leejosepho

    leejosepho DIY scratch-pad engineer

    I was thinking more of knowing where they go so you can later plug something in to assure continuity if you have a circuit or two only feeding outlets.

    Everything you want to test, then check for stray voltage coming back from anywhere just to be sure you do not get electrocuted when you begin grabbing wires.

    Yep, you have the idea going on there.

    No, I think not unless something somewhere is meant to be getting 240VAC.
  7. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    I'm pretty sure that if two incandescent lights are on either side of the phase, sharing a neutral, and I have disconnected the neutral and the hots, that I will find a path down one hot, thru a filament, to the neutral, to the other filament, and down the second hot.

    Thanks for the tips! I am much less awed by the process now.
  8. ActionDave

    ActionDave Electrician

    Messages:
    345
    Location:
    Colorado
    Yes, a clamp on ammeter is the best way to check. With only one half of a three wire circuit heated up the amps on hot and noodle should be the same. With both hots on and a load on both A and B the amps may be different but the amount of difference should be on that circuits noodle. You may find a few tenths of an amp difference.

    Correct.
  9. leejosepho

    leejosepho DIY scratch-pad engineer

    I had not thought of that, and the same could happen with a warm refrigerator on one circuit and a clock on another. So, you might have to unplug a lot of stuff to be able to sort all of this out. If I were the one doing this, I would want to see continuity only between hots and neutrals.
    Last edited: May 16, 2013
  10. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    Use an ammeter and be safe.

    With every breaker in the panel off pick a neutral then start turning on breakers one at a time. This will tell you if the neutral shares two breakers.

    Disconnecting the neutral is a bad idea especially if there is electronics connect to the circuit as electronics do not like being in a 240 volt series circuit.
  11. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    You speak wisdom, Obi Wan. Actually, not much that is designed for 120v much likes 240v.
  12. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
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    There is a lot more designed for 110/120v than there are 220/240v. BUT, if there are devices on both legs of a shared neutral, and you disconnect the neutral it will ALL revert to 220/240 and destroy anything that is not "balanced".
  13. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    Yes, "I've seen 'em blow!"

    Especially back in my film electrician days, which is all about temporary power distribution. That stuff was hairy.
  14. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,264
    Location:
    Cave Creek, Arizona
    My first experience with it was when I disconnected a water heater and the system was "grounded" through the hot side because they had a failed neutral. Disconnecting the cold water supply line discontinued the power flow through the ground and burned out EVERYTHING, (radios, TV, light bulbs, etc.), which was turned on was trashed. I had to carry a console TV out of the house because it was smoking.
  15. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    Bet that cut into your profit.
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