Circuit Breaker Amps

what is CB?

Any value your drill seargent tells you too! as long as it's less than the transformer current rating (876A at 415V OK) and less than or equal to the circuit breaker rating, which in this case is 800A per phase. Any more than 800A and you may trip the breaker out on current overload. Excessively high ambient temperatures may require derating of your 630kVA transformer and 800A CB to prevent overloading in the field.

hi, jak, whats CB? would you like tell me?

CB is short for Circuit Breaker, as in MCB (Miniature Circuit Breaker).

Thanks, figured it, damn electrical "engineers" want to put a 1000 per phase.

if i had to explain what cb was, thought you wouldn't know what i was talking about!

1000A per phase is to much for short-term or continuous operation, but for a very short time it may be ok (like to start up large equipment with large inrush current requirements). In the end it all comes down to what the CB can handle without overloading and tripping out (or getting damaged), and what volt drop is acceptable from the transformer when it is itself overload and its output voltage sags (but it is walking a very fine line between operational and disaster).

It all depends. The T/F rates out 877A. @ 415 V. and 1518A. @ 240 V.

There might be an inrush consideration on the primary, and it's OK

to oversize that 125% or so if you overload protect the secondary.

Some utility type 'low Z` T/Fs do that.

Oil filled T/Fs ride through momentary overloads pretty well,

(thermal mass), but if that sucker is overheating, watch your ass!

Thank you Jack for your reply. now I think hte question is simple to solve.

different links get diffenrt current value.

In a transformer 630 KVA, 415 V you have 876.45 A per phase, you need a 1000 A, 3P, CB -Circuit Braeker for main protection to use the 100% of the transformer.

Good lock in Iraq

LJFF

with ambient temp's over 130 deg F, I derate to only 80% usage. transformers are oil filled.

Is fan cooling an option?

It can boost rating and help with high ambients.

130 F.?? ....in November??

Who supply them electric in iraq