# 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 Thread Starter New Member

Dec 13, 2012
1
0
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 AAC Fanatic!

Jun 22, 2012
5,153
770
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 AAC Fanatic!

Aug 30, 2007
1,154
304
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