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Rotary phase converter questions

joebass

Aluminum
Joined
Apr 3, 2005
Location
NY
I've always had 3 phase in my shopd and never used a phase converter. A buddy of mine just bought a press brake and shear, both have 5hp 3 phase motors. He bought a 10hp phase converter locally. I assumed it was a commercial unit, but it's made by a guy tinkering in his garage. I have a few questions since I'll be helping him wire his stuff.
1) 50 amp 2 pole breaker from his panel to the phase converter wired with 6 thhn. Do we need a disconnect in between?
2) should there be a motor starter and a fused disconnect to the 10 hp motor?
3) what's the best way to feed both machines? Hes a one man shop so they wont be running at the same time. We have square d fused disconnects for each machine.
 

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Disconnect for RPC, yes.

RPC ought to have a motor controller/starter yes. That is assuming the RPC wiring does not also run the load motors.

The best method is to have the RPC only supply the generated leg, in a 3 phase panel which also has the incoming other two (pass thru) wires to it. Breaker for the RPC, breakers for the other machines.

Disconnect before the 3p panel. Best to set it up so the output is not live with the pass-thru power unless the RPC is running. That may involve a contactor on the pass-thru wires that does not close unless the RPC is running. Hit the button for the RPC, and the whole 3p panel becomes live.

Frankly, a lot of folks just run the pass thru to the RPC and onward to the loads, but that does not make it right. The RPC really should have its own controller/starter to give it the proper motor protection. If the RPC controller cuts out, the 3p output should be cut, and not "go single phase".
 
Disconnect for RPC, yes.

RPC ought to have a motor controller/starter yes. That is assuming the RPC wiring does not also run the load motors.

....

The schematic for this particular equipment shows a two pole contactor. Does that contactor constitute a proper motor starter, and if
not then it really does not meet code? Putting a motor starter in there might interfere with the potential relay used to get the start
capacitors on line?

Obviously the breaker supplying the branch circuit for this does the correct job of overcurrent protection for the wiring - but should not
be relied on to take the place of the contactor to energize the idler motor.

I guess over the years I've never seen a diagram for a fancy idler with a motor starter - is this a blind spot in all the designs?
 
.........
I guess over the years I've never seen a diagram for a fancy idler with a motor starter - is this a blind spot in all the designs?

Most likely the assumption is that code required items of that nature will be external to the actual RPC. Those posting the diagrams do not provide "system diagrams". Phase-A-Matic USED TO provide wiring diagrams on-line, including more "system" type diagrams, but do not seem to have them any more.

Various things are required, others are just sensible. Disconnects are required, overcurrent protection for the idler (satisfied by a motor starter) is required.

There is even a code requirement that any single phase loads NOT be connected to the manufactured leg. Most control circuits are single phase, and therefore would be required to be connected to the "pass-thru" legs.

See Article 455 for the entire requirements.
 
I don't know about others in here, but if that is a wood backing I would think that is a poor choice of material as it can retain moisture.
 
I don't know about others in here, but if that is a wood backing I would think that is a poor choice of material as it can retain moisture.


Good eye. I thought it was the tan version of GPO, but it does look like wood. Not the best plan, although the moisture aspect is not that bad, the parts attached should all be insulated sufficiently to begin with, they could be mounted on metal.

Main issue is that wood is "UL- nothing at all"..... it is flammable, not suited for use in the box.
 
Good info so far! So to modify this existing rpc panel correctly what would I need? Links to used stuff on ebay appreciated.
 








 
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