240.40 interpetation. Disconnect prior to fuses.

[gsrandy]

The AHU in my area is interpreting NEC 240.40 defferently than I where we have a fuses at 277 volt 20 amp taping off a 60 amp riser circuit. The fuse holder is designed in a box with tamper proof screws attaching the cover plate. This I feel makes this accessible by only qualified personnel. The fuse will be able to be disconnected and locked off for service if required by the breaker serving the riser.This is an FCU riser on a large commercial project. They are currently requesting a local disconnect for each fuse. What is the opinion of the forum?

 

[infinity]

Re: 240.40 interpetation. Disconnect prior to fuses.

I would agree with the inspector. 240.40 states that a disconnect is required for all fuses over 150 volts to ground. The qualified persons exemption would be for any cartridge fuse less than 150 volts to ground and accessible to only qualified persons.

I would add that I for one wouldn't want to be changing a 277 volt fuse in a live fuse holder. The disconnect requirement is to prevent this from happening where as the disconnect would de-energize both sides of the fuse holder. The cost factor of a fuseholder in an enclosure vs. a fused disconnect is nominal considering the added safety factor of the disconnect installation.