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220v question on lathes

Brent Wells

Brent Wells

Joined
Sep 24, 2014
Messages
24
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2
Location
Akron, ohio
I am getting a 3520b lathe and I did the wiring today for it. I got a 2 pole 20a breaker and ran 10-2 with ground to wire it with maybe 25 feet of wire run from breaker to plug. I know that each line is 110 to 120 volts which gives you 220 to 240 at the plug depending on wire size length of wire and voltage drop and all that. My problem and question is that I got a cheap tester at big box store to test when I was done. I am getting 277 v reading which is considered high voltage. Could this be a glitch with a cheap tester. I am worried about motor and vs inverter. I do not want to plug in and fry something. I will be taking tester to another house to test the 220 there. Should I be worried is this a problem? I am upgrading from a 1221vs so other lathe was 120 v.

Thanks. Brent
 
That's not the first time Ive seen what looks like 140 volts per leg on a split phase system.
There could be a loose neutral maybe in the main panel maybe on the pole.

If that's what you have the condition can be dangerous and a serious fire hazard.
Have an electrician over and consider it something of a crisis condition that should be addressed immediately.

I had a neutral go from rubbing on a tree from the pole. It caused a fire, and blew electrical equipment, and got wires in random places glowing hot.
 
Thanks for response. I have a friend who is certified 30 year electrician coming over. I am still not convinced it is the tester since it is only a light up tester and not an actual digital read out to give you actual voltage. We shall see thanks
 
It could be your cheap tester if it is just some lights (most likely), but it could also be that your wiring is screwed up (not very likely, but possible). 277 volts is significant because that is what you would see in a three-phase Y 480/277 volt system where 480 divided by the square root of three gives 277 volts which is the voltage from any of the three high legs to the current carrying neutral. I can't imagine this highly unlikely scenario happening unless somebody got the wiring wrong back at the transformer. I would opt for spending a few more dollars on a better tester.

If you feel like you are flying by the seat of your pants when adding wiring your home, then you ought not be doing it for safety reasons. Also, you didn't need to use 10 gauge wire. It is basically wasted money for no tangible benefit (unless the wiring run was several hundred feet). The NEC doesn't say that you can't use a larger gauge wire, but it might be prudent to also use a receptacle rated for the wiring size just in case the breaker is changed out for a larger 30 Amp breaker sometime later on. Voltage drop is insignificant with 12 gauge wire in a 20 Amp circuit for typical wiring runs in a home although you will read all sorts of nonsense from Internet experts.

Even in the unlikely event that your line voltage were low for whatever reason, it is not an issue as long as the voltage to the VFD is within the range specified by Delta VFD operating manual (not the voltage specified in the Powermatic manual). The AC power to the VFD gets converted to a DC voltage that is then goes through a circuit called an H-bridge that switches this DC voltage at a high frequency to send pulses to the three power leads of the motor. My point in describing this is to say that in a variable frequency drive, the equivalent voltage to the motor is rarely equivalent to the full 240 volt line voltage except when the motor is running at full speed. At slower speeds as the frequency is reduced the voltage is also reduced to prevent magnetic saturation of the motor.
 
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Thanks Raul and bill as I expected it was the tester. Once electrician came out with real tester I was fine. I have done many many jobs with him and am always extremely safe with electrical. I just went with 10 g for lathe to help with heat and all that since it will be on for extended periods of time, always easier to pay extra and go over board then to do something a second time as my father always taught me. Once I got my fluke tester back I was able to see I was at the proper volts. Thanks again
 
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