Answer / laxmikanta sasmal

breaker rating is selected near to the calculated current of equipment and standard rating of breakers. but it is very important to know the fault current of that
system/ckt where it to be attached.

Answer / kshirod

all are wrong
am telling you a simple method
always follow the thumb rule which is 500kva*1.39=695amp
bt every transformer can take extra 10% amp load

so you can use 800 amp mdo typae 3 pole l&t make acb in the
lt side

Answer / maze one

S = I x V x sq. root of 3
where:
S = Apparent Power, VA
I = Current, A
V = Voltage, V
note : use sq. root of 3 if the system is 3 phase

let's say Voltage = 460V @ Secondary Side
I = (500,000 VA)/(460V)(sq. root of 3)

I = 1,882.66 A

you may multiply the safety factor by 125% to 250%
or using inversed time circuit breaker by 250%

I will use 125% only, that is safe
I = 1882.66 x 125%

I = 2,353.325 AT

Answer / roy

ROUT 3*V*I=KVA
SO FIRST YOU SHOULD MENTION THE VOLTAGE.

Answer / jords

for single phase- 500,000 divided by the voltage times 80% for
your safety factor equals your C.B. size.
for three phase- 500,000 divided by the voltage divided by
square root of three times 80% for your
safety factor equals C.B. size.

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