# Figuring Out RPC Size



## TORQUIN (Apr 2, 2017)

I scored an RPC yesterday. Saw it work and power  an Enterprise 1550 lathe before it was unhooked. The label is unreadable, except for the brand, "Gen-A-Phase", and the seller didn't remember the size. Didn't think to look at the lathe motor's HP for a clue.
How can I figure out the HP of the RPC?







Thanks,
Chris


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## Ulma Doctor (Apr 2, 2017)

if you have an amp meter, you could run the unit and measure the amps drawn.
you could then deduce the HP by amps used

this chart can help guide you...
http://www.engineeringtoolbox.com/elctrical-motor-full-load-current-d_1499.html

just to be clear, you will test the draw of the 2 hot legs of the single phase supply, but you will apply that amp draw to the 3 phase chart.
your amp draw will be slightly higher than the corresponding HP of the motor

for example only,
your RPC pulls  about 11 amps to operate (lightly loaded), you'd then look at the chart and see that a 3 phase 3HP motor running on 230v will pull about 9.6 amps.
knowing that you loose a bit to the electrical gods when you cheat them, you'd then deduce that your RPC would be somewhere near a 3hp output


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## TORQUIN (Apr 2, 2017)

So does that mean I need to wire it up on both ends, then measure amps on one leg of the supply side? How much do I need load it on the 3 phase side? I ask because it will be at "idle" load if there is nothing on the 3 phase side, and even if I connect one of the lathes to it, it will only be at just above "idle", unless I set up to run a heavy cut once it's all wired. I ask this because the web page you linked to states those figures are for full load, unless I'm missing something.
What happens when you overload an RPC? Does it just pop the breaker?

Thanks,
Chris


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## Ulma Doctor (Apr 2, 2017)

you could wire up the input side and guesstemate the HP too, it just won't be as accurate of a test
your values should lower than the full load chart- it is merely a guide

if a RPC is overloaded it should pop a fuse or overload contactor (if equipped), or (then) a breaker if other devices were not used in the system


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## TORQUIN (Apr 2, 2017)

OK, I wired it up, with a 3 phase carbide grinder attached. See pics below.
One leg pulled 12.5A and the other pulled 13.5 at first. After I ran the grinder on it, which only pulled about 1.5A more, and turned it off, one leg was pulling 15.1A until I turned off the RPC and turned it back on.






I have about 240V at the RPC.

Thanks,
Chris


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## Ulma Doctor (Apr 2, 2017)

by deduction, i'd say you have a 5hp unit


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## TORQUIN (Apr 3, 2017)

Thanks for the info.

Chris


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