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+-- Thread: 240V electrical question (/showthread.php?tid=7361352)
RE: 240V electrical question - lincmercguy - 03-04-2021
"One of the slew of issues is keeping the frequency in sync as the generator will vary a little in frequency plus having the sine wave in sync. At the very least the plainer may let the smoke out. Anything you rig up is libel to cost more than running a few wires from the panel. "
Yep, the 240V circuit is just two 120V circuits in opposite phase. The generator and shore power will not stay in sync, and there isn't a safe way to keep them in sync st this level of equipment.
In the proposed setup, the voltage would vary between 0V and 240V as the sine waves drifted on each side. This is typically not very good for an AC motor.
Having a 240V line run to the shop is not as scary and expensive as it sounds. If your panel is full, they do make breakers that take up two spots, but provide one 240V circuit and two 120v circuits. However, new codes are coming soon that require GFCI on 240V circuits in garages/shops. A good electrician can get that worked out.
RE: 240V electrical question - lincmercguy - 03-04-2021
FWIW, I have a Champion generator that has both 240V and 120V. I ran shop tools from them while waiting for electric service. My dust collector was 240V and everything else is 120V, so it worked for that. The generator is a pretty loud solution and a pain to deal with for an extended period of time.
RE: 240V electrical question - Roly - 03-04-2021
(03-04-2021, 01:35 PM)Peter Tremblay Wrote: Thanks Tom,
If I could get to two outlets on different breakers would that count for different poles?
Not necessarily, normally it is every other breaker is the opposite pole. And you should have a common trip between them so if one trips it will trip the other one. Roly
RE: 240V electrical question - TDKPE - 03-04-2021
Sent you a PM, Peter.
RE: 240V electrical question - cams2705 - 03-04-2021
Peter, is your shop anywhere near you laundry room? If you have an electric dryer, you could always branch off of there and just not do laundry and woodworking at the same time.
RE: 240V electrical question - Wild Turkey - 03-05-2021
I "jack-legged" a 220v outlet off of the HVAC unit in my garage back when I was young and foolish.
Worked fine as long as I didn't try to start saw when HVAC was in defrost mode
RE: 240V electrical question - Admiral - 03-05-2021
Fr. Peter: not trying to be snarky or irreverent, but don't you have a parishioner who is an electrician looking for some indulgence credits??
Sorry, I had to ask . . . .
RE: 240V electrical question - MT Woodworker - 03-05-2021
Why not hire an electrician and do it correctly, so no fires, electrocuting anyone?
Safer, and if you ever sell, it is done the right way.
RE: 240V electrical question - MarkSLSmith - 03-08-2021
(03-04-2021, 12:28 PM)TDKPE Wrote: That won't work for a slew of reasons, I'm afraid.
BUT, if you have two circuits in your work space or can get to a second with an extension cord, and if they are on opposite poles in the panel, and if they are both not on a GFCI, then you will have 240V between the two hots.
I once designed a combiner to do that safely, then found that one is already being sold commercially, so I never took it any further. It's not something you want to build, as it takes three relays to prove each 120V leg, then prove that they're 240V between them (it's that, or it's 0V between them), then join them if all is right.
You can also make your own, without relays, but that's a bit like making a suicide cord for a generator, and not something I would detail on an open forum.
I don't understand the need for the combiner thing. If you know that they are on opposite poles in the panel, especially if you can directly verify this via inspection, then aren't they automatically 240V?
I'm asking because I have two dedicated 240V circuits, but I don't have room for another in the subpanel. I do, however, have 2 separate circuits coming from the main panel that I have been considering for eventual addition of a 240V plug in case I need it.
Mark
RE: 240V electrical question - TDKPE - 03-08-2021
(03-08-2021, 08:41 AM)MarkSLSmith Wrote: I don't understand the need for the combiner thing. If you know that they are on opposite poles in the panel, especially if you can directly verify this via inspection, then aren't they automatically 240V?
I'm asking because I have two dedicated 240V circuits, but I don't have room for another in the subpanel. I do, however, have 2 separate circuits coming from the main panel that I have been considering for eventual addition of a 240V plug in case I need it.
Mark
Peter's original question was about using a 120V receptacle, plus a separate 120V generator, to create 240V for a thickness planer. It sort of moved on to getting 240V from two wall receptacle outlets, one each on L1 and L2, to create 240V using a combiner. He doesn't own the place, and it seems it's impractical to wire a 240V receptacle in the shop, though that's definitely the right way to go.
In your case, you can put more than one receptacle outlet on a 240V circuit (I have 6 on my only 240V shop circuit, with 3 machines that use it), just like you can with a 120V circuit that's not dedicated to a single utilization equipment like a water heater or HVAC equipment. Or you can wire those two circuits to supply both 120V and 240V to receptacles, but that's not always easy or practical.