How to Wire a 240V AC Outlet

About: just getting back into Instructables. Hopefully some better projects to come!

We were given a welder that has a big 240 volt plug, but our home doesn't have any 240V outlets already wired. What to do? Wire your  own!

Turns out the plug we had is NEMA 6-50. You can probably figure out what yours is from a chart. If it's close, measure the lengths of the prongs and compare to what is listed. Once you know your plug type, find a mating receptacle on Amazon or somewhere else - probably about $10.

Now go check your breaker box. In most US residential neighborhoods, you'll have two thick wires coming in from the street. These are the mains 240V alternating current (oscillates between 120V positive and 120V negative). Each of the 120V AC outlets in your house uses one of the lines from the 240V pair and one "neutral" line (which has a 0V potential), so the total potential at the outlet is 120V. But we want 240V so we'll have to draw from both lines (poles) at once. For that, we'll need a double throw (2 pole) 50 or 60 Amp (lots of current for a welder!) circuit breaker. Also available on Amazon for about 10 bucks. 

Before fiddling around in the box, turn off the main breaker where the mains lines come in! 

Now fit in your new breaker - it's big enough to span two of the tabs protruding from the rails in the back of the box (one from each pole). 

Get three lengths (one of each red, black, and green) of AWG 8 insulated copper stranded wire (again, very thick for the big currents we're handling) from your Home Depot or wherever. Strip the ends a centimeter or so. 

I only needed to run my wires a few feet into my garage, but you may have to route a longer distance. Poke out another one of those tabs in the side of your breaker box to make room for the new wires. 

Screw in your green wire into the ground rail. Screw your red and black into your newly installed breaker. Screw the other ends of the wires into your receptacle. If you're not installing the receptacle in a wall, be sure to cover the back with some insulating tape to ensure that you don't accidentally short the two liver terminals. 


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10 Discussions


3 years ago

Dude, you don't have a ground in that box, only a neutral. You can't wire a NEMA 6-50 to that box. You did get lucky on one part. 8 ga is ONLY good for 45 amps, but with a welder, you can de-rate the wire. YOU have to put clamps on the wire where it goes through holes to prevent the wire from pulling out and rubbing to wear away the insulation. You also mount your recepticle in a box. I ALWAYS use 6 ga wire and 50 amp breakers for wiring a NEMA 6-50 or 14-50.


3 years ago

Which is the proper wire to the smaller lug on the 50a 3wire plug? Black or white?

1 reply

Reply 3 years ago

Since the two blades of the recepticle are both hot, it does not matter.


3 years ago

i totally agree with almost all of you! this guys trying to get someone voltated! the breaker connection is the last hook-up, not the first! and no grommets? c,mon!


3 years ago

Please remove this instruction set: it is potentially lethal advice in several directions. Even though you throw the main breaker, there is still 240 volt power in the box, just waiting for you to touch it. He says nothing about bringing the wires in through a strain-relief fitting, so in short order the sharp sides of his newly punched hole in the side of the box can skin the insulation from the wire and kill the next guy on the box. He doesn't run his wire through conduit or even tack it down apparently, so God knows all the different ways that can go south. I could go on, but there's no need. The unpracticed person, i.e. those who come to Instructables to learn how to do something, will not know the many ways in which the advice is lethal...let's not find out please.


3 years ago


3wire 240V outlet don't use green neutral line, it uses two hot lines and GROUND line. It must grounded!!!

Before 1996, 3 wire 240v outlet without ground were allowed and only used for some appliance needs both 120v and 240v.

1 reply

4 years ago on Introduction

ohh and by "box" i mean a properly rated gang box that is for the outlet in question!


4 years ago on Introduction

I agree with Groybe, this should be done with extreme caution.

Please be aware that working in a breaker box can and will kill
someone who is not paying attention or does not know what they are

. Insulation tape on the back side is not good enough, it needs to be put into a box, PERIOD!
This is a good start, with a bad finish. In the state that I live in, in my country, we are allowed to wire our own homes, not others peoples houses or business without a licensed (unconstitutional by the way)... the horror stories I could tell you about DIY electrical wiring.
PLEASE if you do not know how to wire, hire someone, it could literally save your life and home!


5 years ago on Introduction

ROFL DIY electrical wiring. All electrical work needs to be done by a licensed electrician for insurance purposes in my country.

Besides that if your gonna have a power point outside the wall mount it in a box and conduit the wires. "cover the back with some insulating tape" just doesn't cut it.

There should be massive warnings about doing any of this instructable. You sort of should mention how you can die if your not careful and even if you throw main breaker it mightn't disconnect neutral and even if it did neutral can still have voltage on it.