Multi motor discconnect size.

[ptonsparky]

I have an existing 200 amp 480v disconnect fed with 2/0 cu.
We are increasing the total connected HP load on this service to 125.
2 - 50 hp
2 - 5 hp
5 - 3 hp

Increase wire to 3/0 and disconnect is rated @ 125 hp. Only the 3 hp motors start at one time. Very close.

Problem is the 5 - 3 hp motors are controlled via a 25 hp VFD. Do I use the actual connected HP to determine the minimum HP rating of the disconnect or include the full 25hp of the drive?

 

[ptonsparky]

This is a Service Disconnect. Feeders to each motor starter & disconnect are sized appopriately.

 

[benaround]

Tom, 430.122 says not less than 125% of the rated input of the drive for the conductors,

and 430.128 says disconnect shall be 115% of the rated input of the drive.

 

[ptonsparky]

Agreed. The drive disconnect would also have to be rated at least for the 25 hp if the 115% did not happen to correspond.

Probably end up with a 400 amp switch & 250 amp fuses, but just trying to see if I figured the 200 correctly.