Size of disconnects

[steve66]

Do fusible disconnects have to be sized for the feeder that supply them, or just sized for the load they serve?

I have a 65A washer and a 85A booster heater about 200' from the switchboard. I am showing a 200A breaker in the switchboard feeding a single set of 3/0 feeders. The feeders run to a 200A fusible disconnect. This disconnect runs the washer. A 3/0 tap runs from that disconnect to another 200A fusible disconnect that runs the booster heater.

Both disconnects were sized for the 200A breaker that feeds them. Could the disconnects have been sized at 100A?

STeve

 

[tom baker]

Re: Size of disconnects

A general rule of article 240 is the conductor has to be protected at its rated ampacity per table 310.16. See section 240.3
There are tap rules in 240.21(B)(1) through (5), take a look at those, to see if your situation applies

 

[earlydean]

Re: Size of disconnects

In the UL white book under switches, dead front (WHXS) and ,enclosed (WIAX) there is a requirement that there not be more than 80% of the fuse size current through the switch. Which means you could have installed 100 amp fused switches for your loads, provided you satisified the tap rules. 240.40 requires there be a disconnect on the supply side of all fuses (where accessible to other than qualified persons) to disconnect each individual circuit from the source of power.