Sizing of Main Circuit Breaker

Thread Starter


Joined Oct 19, 2017
Hi all,
Can anyone teach me how to calculate for the size of a 3pole main circuit breaker?
L1 - N = 30.44A
L2 - N = 32.6A
L3 - N = 30.43A

I know this is a newbie question, but it will be of great help for newbies like me.
Please see attached for the load schedule.

Thank you!



Joined Nov 29, 2005
A circuit breaker is sized to protect the wiring it feeds. The wiring gauge determines the current capability limit that the breaker should not allow beyond and trip at that safe point.

It should be capable of conducting full load, considering also simultaneous starting current of motors.

Thread Starter


Joined Oct 19, 2017
Hi Sir Externet & be80be,

If I use 8.0 as my feeder conductor (50A Ampacity), Is it ok if one of my branches has 14mm sq. and 22mm sq. higher than the feeder conductor?

One of my colleague here, told me that "branch wiring should not be greater than the feeder wiring".

I considered the voltage drop so I was caught up in this situation that some of my branch wires is greater than my feeder wire.

I'll be waiting for your response.

Thank you.