Did I just fry the motor on my lathe? (Plugged into 3 phase by mistake)

So I was visiting my folks place over the weekend and decided to clean up the section of the workshop that has my grandfather's south bend lathe. My parents bought the place from my grandparents about 10 years ago. My grandfather developed alzheimers and didn't get a chance to really get his affairs in order (including the shop).

Anyway, I got the lathe pretty clean and checked all the oil points (still good). So I figured I would fire it up for a few seconds and make sure it would run before doing any more work/ purchasing accessories for it. The shop has 3 phase power, the lathe is a 3 phase (at least from the factory) south bend 14 1/2" lathe, and the plug has a 4 lug type of connector that is identical to the 3 phase 30 ton press (seen to the left of the lathe in one of the pictures).

Well, when the power supply was flipped on, there was a bad sounding hum, and then when the motor ran, the breaker tripped on the power supply. Obviously a bad sign, so we checked the panel and the fuses were fine, the power supply (which was labeled 3 phase) seemed fine. We eventually opened the door to the motor housing and that's when we read the tag on the motor and learned it was single phase!

So my question is, was the motor fried? When we tried to plug it into the 240v single phase receptacle, nothing happens. Maybe we fried something in the power supply? What's the procedure we should follow at this point? Thanks for any help.

Motor Tag (Clearly Single Phase)


Picture of the Work Area


Picture of two plugs (one is for a 3 phase press, the other is the single phase 240v lathe):


Picture of the receptacles:

Ok I pulled the capacitor out of the motor and it looks like it might be damaged. Hopefully it's just the capacitor that blew and not the windings in the motor that fried. I'll do some tests on the capacitor and the motor and see what's up.

Its possible the motor is wired for 220v and the 220v arc welder receptacle is wired 120-N-120-G and the 3 phase receptacle is wired 220-220-220-G

so if you plugged the lathe into the welder outlet you might get 120v or 220v to the motor depending on how the plug is wired and how the outlet is wired, but if you plug it into the three phase outlet you'll get 220v to the motor.


so you need to take the plate off the back of the motor and verify what voltage it is wired for. if its wired for 220 just plug it into the 3 phase outlet. if the motor is wired for 120 then something is wrong. either it blew the breaker because something is wrong, or it blew the breaker because the motor was plugged into twice the voltage it was wired for.


anyhow you may want to go buy a 15 or 20 amp 240v single phase plug and receptacle which will cost you all of 15$ on amazon.


the capacitor looks like it got hot in that one area of the phenolic, but i don't believe you caused it to fail recently, it is probably fine.

I expect the capacitor was just bad, When they fail from overvoltage, you usually know it, loud noise, confetti from inside the capacitor all over, etc.

A bad start cap will cause a humming non-starting motor, That cap does not look good, but does not look as if it were actively damaged. I'd replace it, That dry stuff along the edge may indicate it has dried out, which would mean it was bad.

YOU CAN use any plug type for whatever as long as it can take the voltage and current, but RULE # 1 is NEVER to have the same type plug for two different voltages or systems. change the plug and outlet so those two are different.

So we hooked it up to 3 phase (old school delta ungrounded no neutral) and got these voltages on the starter box:


When we hooked up to the single phase receptacle we got these voltages in the starter box:


I think you might be right. Perhaps it's supposed to be plugged into the 3 phase outlet after all! We're focusing on the starter and the wiring into the motor.

Ok we just figured it out! The starter box was the problem. There's a switch on the starter box that we thought needed to be switched on before using the lathe switch, but it turns out by doing that it caused the humming. Once we reset the switch and left it alone, the lathe turned on just fine! Thanks for the help guys.

i think you have a center tapped delta. that's why you're reading 120 on one leg and 208 on the other. between the two wires (notice the jumper?) you should read 240 volts.

the 80 volts you get from the single phase outlet is not right. anyhow, i don't trust those plugs. is the lathe grounded separately or through that plug?

The lathe is grounded through the plug, we're going to probably change the plugs & receptacles as suggested. That is another good observation about the grounding. We'll make sure it's grounded well when we change it.