Do UL Listed Transformers have to use Fuses if they say Max Fuse...

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fifty60

fifty60

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I have a UL inspector telling me that since the wording on a transformer says "Max Fuse" then I have to use a fuse and not a circuit breaker. I have heard of this on refrigeration equipment, etc, but never for transformers. Is this correct?

The only advantage the fuses would have would be the SCCR ratings...but if I am declaring a 5KA SCCR, then I do not really get any advantage from using fuses right? Is there any other safety considerations with fuses when compared to circuit breakers?

Other than SCCR, CB's are safer in my opinion. They are double pole so both poles or broken, plus they do not tempt the operator to easily use a larger fuse if they are overloading the transformer...
 
I will try to get a picture...it is a table that lists all the max fuse sizes from 380V all the way up to 480V....but the fact that it says "fuses" is what he is pointing out here..
 
fifty60 said:
I will try to get a picture...it is a table that lists all the max fuse sizes from 380V all the way up to 480V....but the fact that it says "fuses" is what he is pointing out here..
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there are such tables for many kinds of transformers but they apply to the fuse blocks you can get with the transformers and are not meant to imply you have to use their fuse block to provide the OCPD.

I have never seen one that says you to use a fuse.
 
The affixed fusing information for the transformer, per the transformer manufacturer, is from the NEC and not from their UL listing. Per NEC 450.3(B), the sizing displayed on the transformer assumes no secondary overcurrentprotection. Since I provide secondary overcurrent protection, I can size the overcurrent protection larger than what is shown on the table, as long as it is compliant with NEC 450.3(B).

450.3(B) only calls out "Overcurrent Protection", and does not only say "fusing". In the subscript notes for 450.3(B) it says "non-adjustable circuit breakers".

The installation is compliant, the UL inspector is apparently satisfied,

A lot of dust but not very many horses, as they say.
 
petersonra said:
there are such tables for many kinds of transformers but they apply to the fuse blocks you can get with the transformers and are not meant to imply you have to use their fuse block to provide the OCPD.

I have never seen one that says you to use a fuse.
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I agree, but I suppose it is possible. It could be that when the transformer mfr went to get a UL listing on their transformer, they used fuses to attain the listing. If they did, and did not ALSO test it behind a circuit breaker, then their UL listing will from that point on REQUIRE the use of fuses of the EXACT kind it was tested with. It's kind of a rookie mistake often made by off-shore suppliers trying to get into the North American market. They usually only make that mistake once, because they find out from customers (or lack thereof) that it makes it difficult to use their product.
 
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