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Thread: USING A CLAMP ON METER TO IDENTIFY NEUTRALS

  1. #1
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    USING A CLAMP ON METER TO IDENTIFY NEUTRALS

    Im pretty sure I did this right. I am moving a panel of circuits over to another panel. There are a few pipes that have more then 1 nuetral in them.
    3hots 2 nuetrals. obviously 2 circuits are sharing a neutral. I need to identify that neutral so that the 2 loads are put on different phases correct? I wouldnt want a neutral feeding 2 hots on the same phase because it wouldnt balance the neutral. It would put twice the load on it. I used a clamp on meter and grouped things together until I got a reading of zero. It seemed to work in all situations. Is this correct? Will 1 hot and its nuetral give me a reading of zero? will 2 hots and its neutral do the same? Is this the way to identify neutrals or is there an easier way?

  2. #2
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    Unless the loads are exactly equal on the mwbc then I would say that is correct. I am assuming there are not 3 hots to one neutral and one hot to the other neutral

  3. #3
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    yea its a single phase system. Each pipe has 1 MWBC and 1 single circuit with a nuetral. Am I right on my other statements about the need to phase them correctly if they are sgaring a nuetral? will having both circuits on phase A double the nuetral load back if they are sharing a nuetral?

  4. #4
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    Quote Originally Posted by green2012 View Post
    yea its a single phase system. Each pipe has 1 MWBC and 1 single circuit with a nuetral. Am I right on my other statements about the need to phase them correctly if they are sgaring a nuetral? will having both circuits on phase A double the nuetral load back if they are sharing a nuetral?
    You are correct. The neutral for a MWBC must have hot conductors from opposite phases. The load on the neutral is calculated Phase A- Phase B= Neutral load.

    If they are are on the same phase then they are additive.

  5. #5
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    I guess you could also check the amps on 2 conductors and see if the difference equals the neutral current. But your method works also.

  6. #6
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    Thanks.

  7. #7
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    green2012:

    Suppose you have many hots and many neutrals and need to sort these out.

    Turn all breakers off except one. Assume there is some load on this circuit. Measure the hot current, then go searching for a neutral with this same current. All other neutrals should have zero current. Label these two wires with the number 1.

    Then repeat on a different hot with all other hots off. Label this hot and its neutral wih the number 2.

    Continue this process with a new number each time.

    Those neutrals with more than one associated number are a neutral of a multi-wire-branch-circuit.

    Any neutrals with more than two associating numbers are a problem.

    The next task is to determine if the hots sharing a neutral are on different phases. Again assume that the hots have loads.

    Turn one breaker on. Put your current probe on the associated neutral. Read the current. Turn the second associated breaker on. If the neutral current diminishes, then phasing is correct. If the neutral current increases, then both breakers are on the same phase. But you could have determined this without the experiment.

    How this experiment could fail. Put a mostly inductive load on one circuit, and a capacitive load on the other circuit. Suppose both circuits are fed from the same phase, then for an appropriate range of reactive values the neutral current would reduce. This is the equivalent of power factor correction on a motor.

    But under normal conditions we do not expect typical circuits to be loaded with grossly different reactive components. So the reducing current in the neutral is probably a good test of the two circuits being on different phases.

    .

  8. #8
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    Why not lift all of the conductors and check for continuity between the ungrounded and grounded conductors?
    This method would require that there be connected loads on the circuits, but so would the methods using current.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  9. #9
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    Should there be any neutrals that are accidentally grounded (shorted to ground) downstream from the panel (and this is not all that rare), you could have issues trying to identify the neutrals and branch circuit conductors.
    Brian John
    Leesburg, VA

  10. #10
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    inregards to phasing correctly, wouldn't you use a double pole breaker anyway, in which case the phasing would be correct?

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