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#14619 - 09/25/02 04:03 PM Transformer Overcurrent Protection  
Electra  Offline
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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#14620 - 09/25/02 08:55 PM Re: Transformer Overcurrent Protection  
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.


#14621 - 09/27/02 11:39 AM Re: Transformer Overcurrent Protection  
Electra  Offline
Joined: Jul 2002
Posts: 38
Portland, Oregon, USA
Thank you very much. That makes perfect sense.

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