Fused or unfused disconnects

[mshields]

Given that unfused disconnects are typically rated for about 14,000 AIC, we always call for fused disconnects at 480V equipment. But much of this equipment, if not all, comes with it's own internal disconnect switch. As such, we are forever fighting the battle as to whether or not an additional fused disconnect switch should be provided.

And not only that, we wonder if we should except equipment with a component not rated for the short circuit.

I'm struggling with what the best approach is to this. Safety is of course #1, but practicality comes into play as well.

All input is appreciated!

 

[tom baker]

The disconnect must have the correct AIC for the application.
Your disconnect appears to be required for a safety application. Even if the equipment has an internal disconnect, it may not meet the requirements of 430.102
I prefer having a separate disconnect next to the equipment, that way all the power is disconnected to the equipment, and a good lock off point for all trades. Then the equipment can be disconnected entirely and replaced.

 

[ron]

The unit mounted disconnect must have the proper withstand for the calculated fault current. The addition of a properly rated fused disconnect upstream of the unit mounted disconnect doesn't help the problem of the unit mounted disconnect being under rated. You must reject the unit mounted disco if it is underrated for the calculated fault current at its place in the distribution system.