Question { 50735 }

MCCB 400 Amps 50KA 430Volt AC
What is mean by 50KA

Answer

50kA means the fault current carrying capacity of said MCCB is up to 50000Amps. Above this rating the MCCB goes trip or damage. The protection capacity is 50,000Amps.

Question { Hitachi, 300360 }

How to calculate cable sizes in sq.mm. with using motor KW?
Any formula there?

Answer

First of all you need to verified full load current of motor,
How can you calculate:
Ex: 1 Motor - 20HP 3ph. 415V 50Hz, 80% efficiency

Cal: A= HPx746/(sqrt3xVoltxPFxefficiency)

=20x746/1.732x415x0.8x0.8

=32.43Amp.

We all know that a motor has 1.5 times starting current,

Then 32.43x1.5 = 48.65Amp

Now you can see in the current currying capacity of cable from manufacturer cable's list.

3.5 x 35 sqmm xlpe cable is sufficient for full load.

Question { Bhutan Power Corporation, 13393 }

IF we have 500kva transformer 11.0/0.415V, 50Hz. How to
calculate the current on HT & LT side, how can we consider
for its breaker (HT & LT both)? You are requested to solve
the question herewith.

Answer

Thanks for answer of this question.
Can you also clarify, on LV side you have multiplied the current with 1.2, why is this??

Also clarify we usually take 3Cx240 & 3Cx300 sqmm Al. cable from HV side. What is the calculation for this cable??