View Full Version : Electrical question

11-08-2007, 12:12 PM
Hi everyone,

I just moved to a new place and my new shop has two 220 outlets, so I figured I'd rewire my lathe for 220 and have one for my arc welder as well. I have a couple of quick questions though. The plugs each say 250V, with one labeled as 20A and one labeled as 50A. Is that the maximum they will deliver or is that what they put out constantly? Am I going to burn up my lathe motor plugging it into a 250V plug? I figured I'd use the 50A plug for the welder and the 20A for the lathe.


11-08-2007, 12:29 PM
Hi Stuart,

The 20A and 50A are the ratings of the circuit breaker, and hopefully the wire gage used for the run to the receptacle. So 20A and 50A are the peak.

You won't burn up a 20A device plugging it into a 50A socket. BUT, 20A, 30A, and 50A circuits all have different plugs and sockets, and you're technically not supposedly to wire a 20A device with a 50A socket.

This may be an issue for your with your arc welder. Most consumer 220V welders are 20 or 30A, but have a 50A socket, for reasons I've never been able to figure.



11-08-2007, 01:11 PM
I would recommend checking the wire size these circuits are connected with, as well as the voltage. The 20A plug should have 12 ga wire and the 50A should have 6 ga, according to my chart. The breakers they are connected to should be equal to, or smaller than the wire and plug ratings.


11-08-2007, 01:30 PM
I believe he was more concerned about the voltage rating on the outlet, 250V is the rating of the equipment(the receptacle itself), the voltage that will be available will be the same there as it will be most anywhere in the area, could be 222 could be 236, anything that is rated 220 will be able to run on voltage that is around +-15% of rated and probably more if it is +. If the voltage is lower it will tend to bog the motor and burn it out, if higher it will run cooler until you get too high and the wire insulation arcs over.

Basically its fine, by the way what is the HP of your motor and the amperage of the welder?

And the multitude of different sockets for 240V is stupid in my eyes, it provides no protection except against blowing breakers if a person doesnt know what they are doing and possibly fire protection for the very stupid that bypass the overcurrent protection of the circuit. I used to run my welder on a 40A outlet and it needed 50 but I just never ran it above 50%.

11-08-2007, 01:35 PM
And the multitude of different sockets for 240V is stupid in my eyes, it provides no protection except against blowing breakers if a person doesnt know what they are doing

Agree. I think the reason that most 220V consumer welders have 50A plugs is to prevent people from plugging the welder into a dryer socket.

11-08-2007, 01:56 PM
Agree. I think the reason that most 220V consumer welders have 50A plugs is to prevent people from plugging the welder into a dryer socket.

Unfortunately, there is no protection for ignorance.

There is no way I care to wire a 30 amp dryer plug with #6 copper, or my 10 amps of baseboard heating with #6.

Electricity is pretty dang simple, if you dont know what you are doing, and dont have the motivation to pick up a book or pick someones brain, call a friggin electrician. I desperately wish the people that owned this house before me would have done that. They didn't know how to split a receptacle, so they wired the top plug under the sink hot for the dishwasher, and wired the ground on the disposal hot switched, then rewired the plug on the disposal.

What I strongly recommend is that you check both lines in the garage to make sure that not only are they sized for the proper sized breaker, but also that the wires are properly installed. :)

11-08-2007, 02:19 PM
Yes I wouldnt expect to have all 220V circuits wired as 50A circuits, just the plugs the same and if you put a 40A load onto a receptacle that says 30A max on it you just blow the breaker. But I guess liabillity says someone somewhere will put a penny in that fuse when it keeps blowing or will change the breaker to a higher rating one without thinking about the wire in the walls.

And after hearing about the nightmare under snowmans sink I'd suggest you check the gauge of the wire running to the 30A and 50A outlets you have Stuart. You probably will be fine but there are all sorts of idiots out there.

11-08-2007, 02:24 PM
Hey, thanks guys. I'll go ahead and call an electrician to check the wiring out first. BTW, the lathe has a 1.5 hp motor and the welder is an OLD Lincoln, model AC-225-S. The label on that says Single Phase 60hz 230V 50A.


11-08-2007, 02:36 PM
Yes I wouldnt expect to have all 220V circuits wired as 50A circuits

I do all my own wiring, and I've pulled most of the 220V runs in my shop as 30A circuits: it's a pain in the ass pulling 6 gage wire through the walls/ceiling.

I did put one 50A/6 gage circuit in for my welder -- that wire is like copper pipe! :)

11-08-2007, 04:14 PM
Check the wire gauge. IIRC they go as follows, but don't quote me:

15A - 14ga
20A - 12ga
30A - 10ga
50A - 6ga

My house had a 200A street drop, but only a 15A wall socket shared with the garage light, door opener, hallway lights, and hallway outlets when I moved in. The first time I used the air compressor, I was in the dark -- and I heard air moving, but that car tire kept getting lower and lower. That weekend, the garage grew 4 20A GFCI sockets each on their own drop. The 220V drops were a few months later -- that 6ga stuff costs an arm and a leg but requires 2 arms and a leg to bend it. I got lucky that the breaker panel lives in the garage and the wall behind it wasn't finished yet.

Yeah, it is more power than I will ever use all at once, but if I thought I could get a 3-phase drop, I'd ask for that too. ;)

11-08-2007, 04:17 PM
I have to add a WARNING about aluminum wire. In the 1970s houses were often built with Al wire for the heavier circuits and attached to plain brass screws and tabs on the outlets and breakers. Al wire attached to brass screws and tabs in plugs can corrode and increase resistance to the point of FIRE.

I know this because I used to be a newspaper photographer and covered many house fires caused by this. My own house came perilously close to burning too. The dryer outlet and dryer line cord plug melted away and I caught it because of the smell. If we'd left the dryer on and made a market run, we'd have had nothing left to come home to (out where we live, all the FD can do is hose down the slab after they get there).

There is a gook you can get at the hardware store to coat the ends of the wire with. Check all your wiring and coat all ends of every Al wire. Don't risk burning the house down.

John Stevenson
11-08-2007, 04:21 PM
Every socket in my shop is wired on a 30 amp ring except for the grinder ones on the front of the welders which are wired direct into the 32 amp feeds.

The bench in the electronics shop for the meters and soldering irons is also wired 30 amp ring. In fact thinking about it there is only the light ring at 10 amps that's not on 30 amp.

Machines are hard wired direct back to panel.


J Tiers
11-08-2007, 10:43 PM
1) Pay NO attention to the ratings of plugs and sockets, until it comes time to attach them to wires (then you need to use the right type).... What is molded into them is MAXIMUM ratings THEY can HANDLE. It may have nothing directly to do with the breaker size so long as the breaker and voltage is no more than the receptacle rating.

2) your receptacles (you wrote "plugs" but you meant receptacles) are presumably rated for no less than what the fuse or breaker iis rated at.
The thing to do is check the breaker to see what the CIRCUIT can supply.

3) The lathe should be OK with a 20A circuit, if that is what that circuit actually is. 20A circuits in general are OK for "general use", although I like to fuse or use a contactor which protects the motor.

4) With the other circuit, the 50A. That is supposed to be a "specific purpose" outlet, as for a dryer, etc. A welder may work in it, but you should covert it to have suitable wiring and receptacle to fit the welder, which probably isn't intended for use in a straight dryer outlet. Dryers used to be wired with a combined "neutral" and "ground wire". I don't think that has been generally accepted for several years now, and in any case your welder isn't made to operate with that type circuit.

Paul Alciatore
11-09-2007, 12:27 AM

You asked if it was safe to plug your lathe into a 250 Volt outlet. Voltage figures are nominal as it is common to refer to the common household Voltage as 110, 115, 117, 120, and even 125. These figures are used almost interchangably and most 115 Volt devices will work just fine with any Voltage in this range. In actual fact, the Voltage may vary considerably during the coarse of a day or week or year and may even go below 110 or above 125 for short periods.

The 220 to 250 Volt range is simply two times the 110 to 125 Volt range as two out of phase lines at the lower Voltage are used to obtain the higher Voltage level. Just as 115 Volt devices will work fine over the entire range and even more, so will 230 Volt devices (220 to 250 Volt devices) work well over the entire higher range.

The important thing is to reconfigure the wiring on your lathe motor for the higher Voltage range before connecting it.

11-09-2007, 08:59 AM
Next question?

Rewiring motors for 220 volts..?? some motors are not as simple as others.
How about the controls? does the lathe have a transformer inside for aux operations like push buttons and contactors? That'll Poof and blow a smoke ring if not wired for correct voltage.

My old leblond is running on a fwd-rev-drum switch. SIMPLE as can be.. just read the nameplate and move the wires to 220 terms. It just series the windings in the motor where 120 is parallel.

Nema 6 plugs is the norm here for welder outlets.. big, little, and round for ground. Stick welders, Them hit a surge of 50 amps when striking a arc, that's why they are on a 50 amp breaker, you size the wire for the breaker protection.

Electricity is nothing to play with, unless you are 300lbs, tattooed and have a death wish. I started at 3 when I wired my rocking horse. My mom knocked me across the room with a economy broom handle. I was so impressed I have not been able to leave it alone.