Current rating for appliance disconnect

[jjirishnh]

WE are replacing an existing commercial dishwasher. The booster heater for the current machine is fed from a circuit breaker rated 70A 480V, this feeds a local disconnect in the dishwashing room. The booster heater for the new machine only requires 50A. We are replacing the old local disconnect with a fused disconnect using 50A fuses. The existing conductors and CB for the 70A circuit remains the same. My question is, when sizing the current rating for the new fused disconnect can I go with a 60A rated disconnect (because I'm fusing at 50A), or do I need to use 100A because the CB feeding the disconnect is 70A?
I think I know the answer here, but would appreciate some insight and maybe a code article reference on how to size these in the future.

 

[kwired]

Feeder tap rules apply to whatever portion you reduce ahead of the overcurrent device.

Keep the reduced size length to less then 25 feet and you are fine.