Breaker size for 10 hp RPC?
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  1. #1
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    Default Breaker size for 10 hp RPC?

    I recently picked up a 10 hp motor to make an RPC. It runs smoothly on 1 ph if I spin it up, and works on a 40A 240V breaker. I plan to buy a control panel for it so it will start and run reasonably well balanced. The question is- What sized breaker for light use? My mill and surface grinder are only 1 hp. I do have a 3 hp 3ph motor I might put in a belt sander. Will these run (one at a time) on the 40A breaker? I know the 10 hp RPC is overkill for my application, but I would like to get a bigger lathe someday.

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    Why not contact the manf. of your RPC. They should be able to tell you right quick.

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    Quote Originally Posted by MushCreek View Post
    I recently picked up a 10 hp motor to make an RPC. It runs smoothly on 1 ph if I spin it up, and works on a 40A 240V breaker. I plan to buy a control panel for it so it will start and run reasonably well balanced. The question is- What sized breaker for light use? My mill and surface grinder are only 1 hp. I do have a 3 hp 3ph motor I might put in a belt sander. Will these run (one at a time) on the 40A breaker? I know the 10 hp RPC is overkill for my application, but I would like to get a bigger lathe someday.
    "Spin it up" takes less amps than the proposed panel's cap start. You could try the forty and see how it does. My 15 cap start uses a pair of 50 amp slow blow fuses in a disconnect with never any issues. This is with 6 AWG about 6 feet long

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    IIRC, my panel called for minimum 30 amp and max 50 breaker, for 10hp setup.

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    I have a 10 Hp RPC dedicated to running a VMC with a 7.5 Hp spindle motor and I have a double 30 amp breaker on it. Never had any problem with it.

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    40A breaker will work fine with your future 5hp lathe even if you run it along with all your present machines.

    Just for a perspective...I use my 15HP on a 60A breaker, and my 7.5HP lathe and 1.5HP Bridgeport with spindles rotating, when work simultaneously, draw only 32A off the 1ph RPC input. The RPC idling alone draws 10A (with 90A starting spike).

    My old Ronk 10 RPC suggested up to 50A breaker.

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    Have used a 20A breaker with a 5Hp rpc for years.

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    My American Rotary panel arrived yesterday, and I'm impressed with the build quality. I'm going to install it right next to my 1ph panel, with a 50A breaker and #6 wire connecting it. For now, I'm going to put a 30A 3 ph rail mount breaker inside the RPC panel, and run a single 3 ph outlet to run my mill. Eventually, I'll wire up a separate 3 ph panel, but I don't need it for now.


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