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Location: IRAQ
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Circuit Breaker Amps

12/11/2006 11:03 PM

When using a 3 P CB, how many amps per Phase can you use?

630 kVA transformer using a 800 amp Main CB.

This is a 50hZ 415/240 V system, somewhere in Iraq.

smilne/ U.S. Army

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Guru
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#1

Re: CIRCUIT BREAKER AMPS

12/12/2006 7:26 AM

what is CB?

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#2

Re: Circuit Breaker Amps

12/12/2006 2:24 PM

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.

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#3
In reply to #2

Re: Circuit Breaker Amps

12/12/2006 9:32 PM

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

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#4
In reply to #3

Re: Circuit Breaker Amps

12/12/2006 9:54 PM

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

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#5
In reply to #4

Re: Circuit Breaker Amps

12/12/2006 11:47 PM

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!

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#6
In reply to #5

Re: Circuit Breaker Amps

12/13/2006 12:48 PM

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).

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#9
In reply to #6

Re: Circuit Breaker Amps

12/13/2006 5:58 PM

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!

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#10
In reply to #4

Re: Circuit Breaker Amps

12/13/2006 8:27 PM

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

different links get diffenrt current value.

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Anonymous Poster
#7

Re: Circuit Breaker Amps

12/13/2006 12:54 PM

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

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#8
In reply to #7

Re: Circuit Breaker Amps

12/13/2006 1:01 PM

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

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Power-User
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#12
In reply to #8

Re: Circuit Breaker Amps

12/15/2006 2:23 PM

Is fan cooling an option?

It can boost rating and help with high ambients.

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

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Guru
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#11

Re: Circuit Breaker Amps

12/13/2006 8:38 PM

Who supply them electric in iraq

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Users who posted comments:

Anonymous Poster (1); cnpower (4); jack of all trades (3); Pragmatist (2); smilne (2)

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