Can someone validate this rotary phase converter design?

[rust buster]

I purchased a 7.5 HP North American Rotary Phase converter to run my Doall 16-3 bandsaw (220V 13.5A 3ph) and Scotchman cold saw (230V 12A 3ph). These would nver be operated at the same time. Both pieces of machinery are 35’ away from my 100A panel and within sight.

My plan is to run #8 wire from the single phase panel to the RPC control on a 40A breaker. Then, out of the RPC control to a 125A 12 space QO 3ph load center via #10 wire. Certainly don’t need 125A, but I had to find one with at least 6 spaces. There will be two 20A 3-pole breakers (one for the band saw and one for the cold saw). #12 wire from the panel to each machine. Both machines have disconnects on them and will plugged into receptacles off the new panel.

Does this pass muster? I’m following the wire sizing guide in the RPC manual, but it’s a strange formula. Am I on the right path?
Thank you in advance.

 

[Bert_]

Breakers all seem a touch on the small side to me, but I haven't done any math.

 

[rust buster]

The RPC manual says breakers in the 3 phase panel should be 1.25x the amp draw of the machines, and calls for 40A max for the breaker in the single phase load center (feeding RPC). Both 3ph machines draw less than 20A

 

[Bert_]

The RPC manual says breakers in the 3 phase panel should be 1.25x the amp draw of the machines, and calls for 40A max for the breaker in the single phase load center (feeding RPC). Both 3ph machines draw less than 20A

That's kind of strange that they call out 1.25x. Most of the time that isn't big enough for a motor to start reliably. NEC allows 2.5x for a normal circuit breaker.

Motors usually start harder on a rpc vs real 3 ph.

 

[wyliesdiesels]

I also suspect the breaker may be a little small.

What does the RPC use to start the idler motor?

 

[walta]

The RPC manual says breakers in the 3 phase panel should be 1.25x the amp draw of the machines, and calls for 40A max for the breaker in the single phase load center (feeding RPC). Both 3ph machines draw less than 20A

I agree since only one machine will be operating at any given moment it seems the current max load is 13.5 Amps so 40 should be fine.

Consider adding a set of panel Volt/Amp meters to your set up. Making it easy to monitor the converters performance.

Amazon.com

Walta

 

[rust buster]

I agree since only one machine will be operating at any given moment it seems the current max load is 13.5 Amps so 40 should be fine.

Consider adding a set of panel Volt/Amp meters to your set up. Making it easy to monitor the converters performance.

Amazon.com

Walta

Great idea. I did order the voltmeter with the RPC, but an Amp meter was not an option. Definitely will grab one. Thank you