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  1. #1
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    Sharing the neutral

    When you come across places where they ran 12-3 MC to 2 circuits , and each circuit pulls 20 amps , I have to wonder how the neutral carries the current for both since its alternating current.....

  2. #2
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    If you mean a Multiwire Branch Circuit ("it's a thing"), then...

    ...the two circuits, fed from a tied dual breaker and feeding a string of receptacles, will have currents that are 180% out of phase with each other, so that the peak currents never happen at the same time.

    I don't like them. If a neutral comes loose, the voltage can jump to 240. It happened at our church, and the entire audio system blew out to the tune of 10 thousand.

    Here is an article:

    https://www.ecmweb.com/content/artic...n-be-dangerous
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist
    Member, IAEI

    AOP Forum Rules:







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  4. #3
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    I saw one yesterday where a double pole 20 had the strap removed from the trip levers. 12-3 went to coffee machines pulling 15 amps each ( 2 machines ) and 1 neutral going to panel

    Why would they remove the strap ?

    Would it be better to shove a wire thru the levers to make it a true double pole .... so they both trip ? ( ive seen bare 10ga used alot )

    ( seems like im always having to tidy up panels )

    Any time i see something like this I always grab my flat screwdriver and snug the neutrals in the panel , largely because I have witnessed what happens to machines that saw 240v because the neutral come loose

  5. #4
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    Quote Originally Posted by Snapperhead View Post
    I saw one yesterday where a double pole 20 had the strap removed from the trip levers. 12-3 went to coffee machines pulling 15 amps each ( 2 machines ) and 1 neutral going to panel

    Why would they remove the strap ?

    Would it be better to shove a wire thru the levers to make it a true double pole .... so they both trip ? ( ive seen bare 10ga used alot )

    ( seems like im always having to tidy up panels )

    Any time i see something like this I always grab my flat screwdriver and snug the neutrals in the panel
    You need to replace the breaker, not further modify it

    Sent from my Moto Z (2) using Tapatalk

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  7. #5
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    On these curcuits, the Neutral carries the imbalance of the two hots (which are on the different phases).
    If L1 was drawing 10 amps & L2 was drawing 15 amps, the neutral would draw the imbalance so 5 amps.
    At my trade school there was a demo board on this in the Electric shop.
    It had various incandescent lightbulbs and with the L1 & L2 loads ballenced, you could disconnect the neutral.
    But God forbid out in the real world if a neutral get disconnected.
    The leg with the most sensitive load gets fried as it’s now two 120v loads in series with 240v!!!
    Eric

  8. #6
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    Picturing it in my head. So with a tied 2 pole breaker I see your point it will cause the whole breaker to trip both power legs. Or with the tying bar removed from the double pole breaker. Then the neutral wire falls out from the circuit as others said it then becomes 240v feeding the 120v load. So how about running two single pole breakers tapped on the same hot buss bar. Between the 2 breakers it will be 0 volts since it’s the same leg. If the neutral cuts out all loads shut down. This seems like it can be legal??? Probably for electrical code each circuit needs to have its own neutral wire pulled. This is probably why in a breaker panel the neutral bar bar would have 10-20 different small lugs on the neutral bar. I’M not saying it’s true. Just asking and picturing it all in my head.
    Sent from a mechanical closet!

  9. #7
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    I clicked thinking this was a thread about a threesome with a hermaphrodite.

  10. #8
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    Quote Originally Posted by Adlerberts-Protege View Post
    I clicked thinking this was a thread about a threesome with a hermaphrodite.
    https://m.youtube.com/watch?v=RFlCD5CYAcU

  11. #9
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    Thread Starter
    Quote Originally Posted by anthonyac1 View Post
    Picturing it in my head. So with a tied 2 pole breaker I see your point it will cause the whole breaker to trip both power legs. Or with the tying bar removed from the double pole breaker. Then the neutral wire falls out from the circuit as others said it then becomes 240v feeding the 120v load. So how about running two single pole breakers tapped on the same hot buss bar. Between the 2 breakers it will be 0 volts since it’s the same leg. If the neutral cuts out all loads shut down. This seems like it can be legal??? Probably for electrical code each circuit needs to have its own neutral wire pulled. This is probably why in a breaker panel the neutral bar bar would have 10-20 different small lugs on the neutral bar. I’M not saying it’s true. Just asking and picturing it all in my head.
    if you read posts 2 and 5 you will see being (180 degrees out) helps save the neutral from getting too many amps

    So you pretty much have to keep them on different phases

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