Do I need to derate fused disconnect?

[dpmsrm03]

I am installing a fused disconnect downstream of a distribution panel breaker. The fused disconnect will be used to provide local disconnecting means for a "power buggy" type device of which will essentially be a portable load center. The "power buggy" will be connected to the disconnect during times of operation when additional temporary power is needed.

The OCPD in the panel is a 250 ampere breaker. My question is, do I need to derate the fuse's in the disconnect down to 200 amperes (125% of OCPD) or can I use 250 ampere fuses. The "power buggy" will have breakers for each available load position just like a distribution panel would. I have looked through the NEC, but cannot locate an article giving me good information regarding this type situation.

My other choice would be to use a non-fused disconnect.

Thanks in advance for the help.

 

[ron]

If the upstream breaker is providing the required protection, you can size the fuses as high as the disconnect is rated.
The buggy is rated for a 250A feeder?

 

[infinity]

You don't even need to use a fused disconnect since the feeder is protected by the 250 amp OCPD upstream of the feeder. You can install the same size fuses at the fused disco if you choose. As Ron mentioned you conductors need to be sized at not less than 250 amps.

 

[dpmsrm03]

Thank you for the replies. I have looked through the NEC to find reference to this type setup and I had no luck. Any chance of driecting me to the section of the code I could read up on for this application. Conductors are sized accordingly. If I use same sized fuses, I guess I do run the risk of tripping the upstream OCPD as well as the fuses.