Three phase power

Ron has a pretty nice generator, even tho it is 3 phase 208. Still very usefull as each phase is 120 volts to neutral. If a machine needs single phase 120V, just connect it between neutral and one phase of the 208 system, and you have 120V. Connecting between any 2 phase legs of the 208V system will give you single phase 208V, which is often OK for machines specified for single phase 220V. If you have one of the rare devices that really requires 220V, a buck-boost transformer can provide it from the 208V line.

Bill I cant remember if your chunker motor is 240 or 220.

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I also learned that if you want to aggravate a plumber, call your water heater a hot water heater.


Hahaha Joe. Never aggravated, all in fun.
I did look at my motor and says 230 volts. All honesty, I don’t know the difference. I figure there just must be a range of voltages that’s acceptable?

ahh 230. So with Rons generator you could give the motor 220, which would cause the motor to run a little hotter and have about 4hp instead of 5 (just throwing those numbers out there, could be more or less HP loss, but it will be a loss) So it could be done, but it wont be as efficient. The 240 volt service at your house would work to its full potential.

That makes sense to me. How does 208 volts come in to play?

basically, a 208 volt system will show 208 volts on the meter if you measure from phase to phase. That means put one meter lead on one “hot” and the other lead on another “hot”. If you measure from phase to ground (or neutral) 1 lead on a hot, 1 on ground, you will show 120 volts. Pretty sure 208 volts wired in “delta” does not require a neutral wire. So if you were to take say a 230 volt or even a 240 volt system and hook it to a 208 volt system (rons geny) using 2 phases of the 208v ( 2 120v legs) it will be derated by 25% or so. The difference between 208v three phase, and 240v single phase, is how the voltage is taken.

Like this:
240v single phase is created by taking a single leg of three-phase power.
208v three phase is created by taking two legs of three-phase power.


Thanks for the explanation Joe.
I’ll stick to plumbing. :smile: I can’t hurt myself.


Hi Joe, I have to mention to keep things safe, on a 3 phase delta one hot leg well be higher than the other you can’t use it for 120v. Al

yep, the “wild leg” i think its called.

A few good videos here.



This explaines why Rons geny had continuity between phase and ground. it was wired in wye. Tom Wobig corrected me here.


That delta wye was a lesson learned the hard way so it stuck. Wish somebody would have told me.
New machine arrived got installed Master electrician wired it up . powered up breaker trips.
Showing short from phase to ground. Time spent trying to get to transformer. Finally get schematic sent to us. Turns out electrician marked two ends of wire for ground but not on the same wire


Like the elect. in a hurry and uses 4 black wires . . opps! I guess that wasn’t ground afterall. :boom:

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Grid voltage varies a fair bit, if the motor is single phase, 230 or 240 I would hook it into the 208 and not worry about it. Extremes will bother a motor but unless the 208 is unusually low it should be ok.

Rule of thumb if you can keep the variation under 10% most things are fine on 208.
Low voltage increases the demand current increases and the motors tend to run a bit hotter.
The power equation must be balanced ( lower volts means more amps required to give you the same power output ).
Most motor are rated to run at 10% more amps than the nameplate just in case of low voltage.

Heaters and lights are not adversely effected by low voltage, you just get less heat and dimmer lights ( except Florescent lights that do not like low voltage at all and can be damaged )

Some 3 phase generators can be rewired to produce single phase.

This is why I always suggest Solar panels and an overspec’d inverter… then you hook your generator to the inverter to have that take care of everything even if you have to use rectifiers go to dc first, it skips a lot of hassle. :slight_smile: (understandably, it isn’t always the right choice… )