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Feeder Breaker Sizng for Dry type transformer

Feeder Breaker Sizng for Dry type transformer

Feeder Breaker Sizng for Dry type transformer

(OP)
I am sizing a feeder breaker for a 112.5KVA Transformer(600v/208v). As per Canadian Electrical Code.The primary breaker shall be sized not larger than 1.25FLA (Pri)if the secondary breaker is sized larger than 1.25FLA(sec).Therefore I chose 150A FDB cutlerhammer Circuit breaker.But it is also noticed that this breaker may trip on inrush current(12FLA). In this case. can we choose a larger size of CB, like 200A. or alternatively, we can choose a different type of CB with adjustable digit trip unit.

Any inputs would be appreciated.       

RE: Feeder Breaker Sizng for Dry type transformer

Historically, breakers sized per NEC have been proven adequate for standard dry type transformers.

Rafiq Bulsara
http://www.srengineersct.com

RE: Feeder Breaker Sizng for Dry type transformer

FLA = 108 Amp
12FLA = 1300 Amp
150 Amp breaker @ 10X instantaneous setting = 1500 Amp.
Another option may be to down size the secondary breaker to 1.25FLA(sec)  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Feeder Breaker Sizng for Dry type transformer

(OP)
12FLA = 1300 Amp
FDB 150 Amp breaker has a fixed characteristic. The instantaneous settings range between 800A and 1600A.
 

RE: Feeder Breaker Sizng for Dry type transformer

Yes.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Feeder Breaker Sizng for Dry type transformer

150 is probably OK if you set the instantaneous up.

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: Feeder Breaker Sizng for Dry type transformer

the code refers largely to wire ampacity when describing when and of what size of protection is required. You do not mention wire capacity, so sizing of protection is mute.

RE: Feeder Breaker Sizng for Dry type transformer

NEC (and CEC I presume) has specific requirements (limitations) on transformer protection as well.

Rafiq Bulsara
http://www.srengineersct.com

RE: Feeder Breaker Sizng for Dry type transformer

Yes Rafiq, CEC also. Wire ampacity protection tables are for use where not otherwise specified.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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