how to calculate 3 phase breaker size with given single phaee load amperes

Discussion in 'General Electronics Chat' started by XEB, Dec 13, 2012.

  1. XEB

    XEB Thread Starter New Member

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    Dec 13, 2012
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    i want to calculate the size of a 3 phase main breaker of a workshop which has all single phase industrial sockets with total current of 2125 Amp.

    40 sockets of 30Amps 40*30=1200
    35 sockets of 20 Amps 35*20=700
    15 sockets of 15 Amps 15*15=225
    =2125Amps

    what load distribution should i do?
    and what would be the 3 phase main breaker size?
  2. Dodgydave

    Dodgydave Well-Known Member

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    Well if your using single phase sockets then you need to be using single phase breakers, as the sockets will have to be evenly distributed across all 3 phases to balance the loads.

    Also if you work on the fact that all the sockets wont be used all the time, and work on 75% rule that will be
    2125A * 75% is 1600 amps approx over 3 phases gives approx 530 amps per phase THATS A LOT OF POWER !!!


    Have you got that?
    Last edited: Dec 13, 2012
  3. gerty

    gerty Well-Known Member

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    In most cases that's true!
    But he hasn't told us the application yet, if it's some sort of factory most of them may very well be on at the same time.

    XEB: you need to give us more information, are these individual circuits going to machines that will be running most of the time?
    Or are they going to recepticle circuits in a mall where not much of anything will be plugged in/turned on?
    Last edited: Dec 17, 2012
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