Disconnect Sizing

[WastefulMiser]

Is it OK to size a disconnect at rated current v. what the OCPD is?

Ex:

75kva xfmr, 480P, 208Y/120S, the OCPD is located elsewhere for the primary and is sized for 250% rated primary current.

Is it OK to size the local disconnect 75000*1.15/480/1.7321?

 

[ceb58]

A disco will need to be rated for the voltage and at or above the amp load.

 

[cpal]

Is it OK to size a disconnect at rated current v. what the OCPD is?

Ex:

75kva xfmr, 480P, 208Y/120S, the OCPD is located elsewhere for the primary and is sized for 250% rated primary current.

Is it OK to size the local disconnect 75000*1.15/480/1.7321?

Which Code cycle are you installing under, is the disconnect on the pri or sec?? and why are you installing it??

 

[nakulak]

are you talking about fusing down the disconnect ? (yes)

or the rating of the disconnect ? (no)

 

[WastefulMiser]

Which Code cycle are you installing under, is the disconnect on the pri or sec?? and why are you installing it??

Primary.

NEC 2008.

LOTO. Local disconnect next to the transformer. What the end user wants.

 

[WastefulMiser]

are you talking about fusing down the disconnect ? (yes)

or the rating of the disconnect ? (no)

This will be a non-fused disconnect.

And yes, the rating of the disconnect. Is it OK to use a 100A, 600V disconnect?

 

[curt swartz]

What size primary overcurrent protection and wire are you planning to use. You mentioned sizing it a 250% so it will be impossible to terminate this large of wire in a 100 amp disconnect.

 

[WastefulMiser]

What size primary overcurrent protection and wire are you planning to use. You mentioned sizing it a 250% so it will be impossible to terminate this large of wire in a 100 amp disconnect.

Thanks for the reply.

Ideally I guess 225A, so I believe that is a 4/0 without looking at the chart.

But you have a good point about the termination. I guess I should verify if 100A disconnect lugs can handle that size of a cable.