UL 508A Non-Fused Switch and Main Contactor Sizing

[Spanetti]

I need to size the main contactor and a disconnect switch in a panel to be built by a 508A shop. I have multiple blowers and motors after the contactor but some of them are installed spares that will only run when others are offline. Can I size these parts based on normal operation or does UL have a requirement that I need to follow?

Thanks

 

[Jraef]

I need to size the main contactor and a disconnect switch in a panel to be built by a 508A shop. I have multiple blowers and motors after the contactor but some of them are installed spares that will only run when others are offline. Can I size these parts based on normal operation or does UL have a requirement that I need to follow?

Thanks

115% of the total load, minimum. Motor loads must be determined based on the tables in article 430 (not the FLA on the motors, unless the FLA is greater than the table). It's laid out for you in 430.110, UL follows the same rules.

Side note: you will likely end up with an SCCR on that panel of no more than 10kA, which will make it difficult if not impossible for the installing contractor to connect it. NF disconnects are not rated very high, unless you can dictate the up-stream fuse size and type ahead of it. To get a decent SCCR rating, you are better off just using a Fused Disconnect or circuit breaker, even if it is redundant.