Single vs three phase current

[Chris Barnett]

Powermatic manual says to use wiring that is matched to current shown on motor nameplate, which is 6.2 amps. That current is at 3 phase 220, so what is current rating required for single phase?

[Steve Schlumpf]

Chris - I'm not an electrician but I do have the Jet 1642, 220 volt, 2 hp and wired my own shop to run it. I have the same current listed on my motor and that is the current per leg of the single phase connection. The motor is 3 phase but the controller actually generates the phase difference to run the motor. I know Powermatic does offer a 3 phase lathe but am pretty sure you would have had to special order that. The actual wire that you use would depend on how far you have to make the run. I ran almost 40 feet and used 10 gauge which is a bit of an overkill but I wanted to err on the safe side. Hope that helps.

[Matt Hutchinson]

The phase and voltage of the supply has to be the same as the motor (although it's easy to take 110 supply up 220v). If you only have single phase supply, you need to have a phase converter of some type. If this can't be done than you're gonna need a single phase motor.

Hutch

P.S. My mistake. I thought you were referring to a machine that didn't already have a VFD/converter on it. Never mind.

[Mike Henderson]

I can't give you an exact answer, but I can give you an estimate.

To calculate the VA into your motor, you multiply 220V times 6.2 amps, times square root of three (about 1.732), or about 2400VA (rounded).

Your input to the VFD is assumed to be 220V single phase, and let's assume a conversion efficiency of 70% (the VFD uses 30% of the power to do the conversion). Divide 2400VA by (220V *.7) and you'll come out with about 15.5 amps. So my estimate is that you should plan for a 220V supply at 20 amps to feed your VFD.

Mike

[scott schmidt grasshopper]

hi all . I just had my new to me PM 3520A installed by the electrician and,,,,
takes a 20 amp 220 single phase line
my owners manual says it can be run off 3 phase but other than farms and industrial areas 3 ph is hard to find ( its a special wire set up off the main power company grid)
electrician said. the wiring had to comply with the plug besides the motor. so you probably have a 20 amp plug ( ps its really only 16 amps or so max cause code says you are allowed 80% of capacity of the wire/ breaker. hope this clears it up.

[Chris Barnett]

Thanks much for the help.
The motor is 3 phase and the nameplate lists the motor current but only for 3 phase, so when their manual says to use the nameplate current data to size an extension cord, they are erring because the input to the lathe,i.e. the phase converter box, is single phase, and current is much higher than for single phase. I did not remember how to convert for 3 phase, probably went over it back in school but that was a long time ago. Also thought a 15 amp breaker would be adequate but seems I need a 20 minimum....way higher than I would have anticipated. That's why I am mechanical-nuke.
A friend who was an electrical engineer (an engineer's engineer, some of you guys will know what I mean, a seat of the pants engineer with papers, who gets his hands dirty) was always there to answer the electrical questions. He passed on recently, so will be posing my electrical issues here. RIP Tony.