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I am installing a 30 HP three-phase rotary converter on a 200 amp service in my home shop. I intend to run a CNC milling machine with a 15 HP motor. I am using 2 AWG wiring in 1" shielded conduit from the panel to the converter, and from the converter to the machine. I'm using a 150 amp breaker at the panel. I am really just asking if there is anything I should know or look out for with this type of project, and if the materials I've selected are appropriate. I would love to hear from anyone with experience installing 3 phase rotary converters.

Thanks for your time!

Han Yolo
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  • Does the CNC use a VFD's or a start-delta starter with gearbox? – Jeroen3 Oct 09 '20 at 19:29
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    Honestly this is the sort of thing where you probably want to consult with your fellow machinists, it's a bit obscure to address from first principles. A rotary converter makes sense if you have a direct line-connected motor and don't want to upgrade it to a VFD. If the target machine already has a VFD, then what you should probably do is consult the derating tables for operating a VFD on single-phase input. Since a VFD rectifies the mains to produce a DC rail anyway, they can operate on single phase, but this places more stress on the rectifiers and capacitors so they have to be de-rated. – Chris Stratton Oct 09 '20 at 19:36
  • Since you have not stated the voltage or the type of wire but stated the wire size in AWG, I will assume 240 volts and 75 degree C wire. That would be good for 95 amps and provide 22.8 kVA.safely. 15 Hp is about 11.2 kW. Dividing that by 22.8 gives you an allowable minimum efficiency x power factor of 0.49 and rated motor load for your drive system. My guess is that your system will achieve that. I think current rating of the circuit breaker may be too high. I assume you can get away with wiring for the motor rating rather than the converter rating. –  Oct 09 '20 at 21:41

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