Making a 240v ac cord from two 120's

[T-Sport]

I saw a guy make a 240v ac cord by combining two 120's on seperate circuits. :confused: I know that could be kind of risky but rather than putting in a 240v outlet, I do have two 30 amp circuits in my garage that are very close to one another and would like to construct a cord correctly without toasting my toaster. Anybody out there know where some good diagrams are for this? BTW: I'm using a Miller 150 STH.

[Sandy]

I saw a guy make a 240v ac cord by combining two 120's on seperate circuits. :confused: I know that could be kind of risky but rather than putting in a 240v outlet, I do have two 30 amp circuits in my garage that are very close to one another and would like to construct a cord correctly without toasting my toaster. Anybody out there know where some good diagrams are for this? BTW: I'm using a Miller 150 STH.

This is one of those things you're not going to get a lot of advice on. Not because it can't be done but because there are just too many variables to be handing out blanket answers to. A person would have to be right there and see the layout. There was some discussion on this a couple of times before, and I think it was in this section. You may want to do a quick search.

Here's a few things to think about:

Your Sub panel/breaker box have seperate ground/nuetral busses or combined?

Do you have any GFCI circuits off this panel?

What else is on each of these two 30 amp circuits?

Two hots and a ground--which ground would you use? Or combine both?

[Pentawelder]

Sandy is absolutely right, it's easy to do IF ...
One other thought, if you have a fire from any cause
the fire folks and particularly the insurance company
will lock onto this unconventional and possibly illegal
connection and blame it for the fire.

[halbritt]

If it's your garage and you intend to do this more than once, it'd probably be more prudent just to install a 240VAC outlet.

If the two 30A circuits are on either leg of the panel, you should be able to measure 240VAC across the two hots. You could build a box using parts from home-depot with a couple of cords and a 240VAC outlet. Tie the hot from either circuit to either hot on the 240VAC outlet and then tie the grounds from either cord into the ground on the 240VAC outlet. Plug the cords into either 120VAC receptacle. If you smell smoke, then be concerned. If you see fire, then you should run. Otherwise, you should be able to measure 240VAC across the two hots on your receptacle. If you only get 120VAC, then there's a mistake somewhere. If you get 0VAC then you forgot to plug it in. Good luck and uh... God bless.

[rbucc]

halbritt's right it is very easy to install a new outlet. Alot of contractors I know use
the adapter you discuss on job sites for temporary 240 hookups. I actually was using
my 30A 240v clothes dryer outlet until my garage addition was fully wired. Go and look at your main panel, 30A 120v circuits are usually rare in a residential home, look for the 30A breakers and see if they are on the opposite sides of the panel, and offset
up or down an odd number of spaces (even spaces would be the same leg). If so, try the cheap and easy cord method. But consider a dedicated outlet, it will give you better performance with the welder.