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Transformer Overcurrent Protection #14619
09/25/02 03:03 PM
09/25/02 03:03 PM
Electra  Offline OP
Joined: Jul 2002
Posts: 38
Portland, Oregon, USA
My question is concerning transformers over 600V. The sizes of fuse or circuit breaker protection is based off of Table 450-3(a) (1999 Code).

Why is the size of a circuit breaker permitted to be larger than a fuse?

I thought that fuses would offer better performance and therefore be allowed to be rated higher.

I thank you for any guidance you can give me on this.

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Re: Transformer Overcurrent Protection #14620
09/25/02 07:55 PM
09/25/02 07:55 PM
Ron  Offline
Joined: Mar 2002
Posts: 582
White Plains, NY
You will find a similar situation for motor short cirucit protection from Table 430.52. Fuses get set tighter to the load than breakers to avoid false trips.

Re: Transformer Overcurrent Protection #14621
09/27/02 10:39 AM
09/27/02 10:39 AM
Electra  Offline OP
Joined: Jul 2002
Posts: 38
Portland, Oregon, USA
Thank you very much. That makes perfect sense.


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