Reply to "Extension Cord Size."

Ron,

If your welder draws 40 amps on the primary (high voltage side) and the voltage at the receptacle is 230 volts, then the voltage drop is:

200', #6 wire = 2.9% or 6.7 volts
250', #6 wire = 3.6% or 8.4 volts
250', #4 wire = 2.3% or 5.3 volts

The length above is from the receptacle to the welder (total of the extension cords + the welder cord), and does not include the voltage drop between the receptacle and the main panel (or to the transformer). Wire is copper.

The #6 wire at 250' is marginal but should work, but if your welder has any electronic controls, then use the #4 cable (as Julian suggested). It's a lot cheaper to buy the next size larger cable than to buy a new welder.

The cable is referred to as "6/3 (or 4/3) SO cord". The 6/3 means #6 wire, 3 conductors. SOO and SOOW cord are equivalent. Figure on $$$ per foot.

Your jobsite probably has 240 volts, which will reduce the voltage drop slightly.

One other consideration is if the building has three phase power. If it does, the available voltage may only be 208 volts. If it is 208 volts, then use the #4 cable.

John