I've been wondering, how should I select the contactor size for my RFC? I'm building it with a 30hp motor so I know there will be a substantial in-rush current to get it started. Do I need to account for that in-rush current by getting a bigger contactor or are they made to handle short spikes in current without damage?
Your idler motor dataplate figures are all THREE PHASE ones. Single-phase service to it for use as an idler will involve higher current.
Allow for that and the contactor should be OK with the associated inrush too.
The RPC starter/controller "manages" that startup, but that is not the same as magic. It will need serious power to it.
How much?
Simplest to use what the maker of an RPC starter/controller for a 30 HP idler says to use in their specs.
Don't HAVE such a manual?
No fear.
Just use the specs from some
other commercial 30 HP RPC maker.
Or the many in PM's "stickies"!
And/or check
several of the major maker's specs and make your choice.
You might not expect it, because their nature at start-up is very different, but @ 10 HP, my Phase-Perfect actually wants almost identical single-phase service amperage as my factory-bought @ 10 HP idler RPC starter/controller specifies.
Manual being handy for the 30 HP Phase-Perfect, those figures are:
136 AMPS of single-phase to deliver 80 Amps sustained "steady state" to the 3-Phase load. That also supports a peak of 96 Amps for a shorter while, and a surge of 400 Amps.
So if I HAD a 30 HP P-P? I'd use a 150A 2-pole breaker, #2 copper wire, and a contactor comparably rated on the input side.
No harm to use an
oversized
contactor. But the wire and breaker have to meet code.
So much for one set of specs. You can find more to compare in the PM RPC stickies.
Hopefully other PM'ers will have other numbers to share "shortly".
Hopefully you have 400A service, too!