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Shared Neutral Current Additive 120/208?

Discussion in 'Electrics Outside of the UK' started by donniet1977, 9 Dec 2013.

  1. donniet1977

    donniet1977

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    I'm remodeling my kitchen and am bringing it up to code. My service is 120/208. I wired up my first multiwire circuit. I decided to read neutral current flow with a clamp on ammeter to make sure everything was cool. I had a 1 amp load and a 2 amp load on the two hots. I expected to see something less than 2 amps on the neutral but was surprised to see the full 3 amps. The hots are fed from opposite busses. Can anyone help me figure this one out?


    Thanks,

    Don
     
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  3. Lectrician

    Lectrician

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    Must be on the same phase (hot line).
     
  4. donniet1977

    donniet1977

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    Nope. 208V between the two.
     
  5. Lectrician

    Lectrician

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    Then your clamp meter is wrong.

    What loads are these?
     
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  7. donniet1977

    donniet1977

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    Refrigerator at 1 amp and 3/8" drill motor at 2 amps. I was using a cheap off brand clamp on ammeter but it doesn't seem that would be the culprit here. I might have to increase load and test again.
     
  8. Lectrician

    Lectrician

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    You could run into odd readings at low loads, and also with inductive/capacitive loads too. Many cheapy clamp meters are no good at low currents. There are also harmonic currents to consider.
     
  9. donniet1977

    donniet1977

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    After more thorough testing I am even more troubled.

    Quick recap: My service 120/208, hot to hot is 208.

    With an 8.5 amp toaster oven on one circuit and 11 amps on the other circuit which feeds the fridge (about 1 amp) and space heater (temp) my neutral current reads 19.2 amps. I'm using an Amprobe ACD-15 Pro clamp on ammeter. This condo has been wired with mostly MWBCs ever since it was built from what I can tell. Have the neutrals been overloaded the whole time?! I'd really like to get on the feed to my panel which is just a subpanel but I just don't have the room.



    Thanks,

    Don
     
  10. donniet1977

    donniet1977

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    I'm both embarrassed and happy to say that after further troubleshooting I discovered that the outlet we wired temp for testing was miswired and being fed by the wrong circuit. This led to all loads being on the same leg. I was a little lazy in my initial troubleshooting and made too many assumptions. One assumption was that there was a problem in the first place.

    I think the initial problem I saw with the 3 amp neutral was simply due to low inductive loading along with meter creep.

    Final Reads Ignoring Fridge (<1 amp) which is always on:

    CKT 1 on 2 off - In=9.1A
    CKT 1 off 2 on - In=11.9A
    Both CKTs on - In=12.0A

    Thanks for the replies.
     
  11. DIYnot Local

    DIYnot Local

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