Originally Posted by KTM640Dakar
You have it backwards.
Yes an extension cord will raise the resistance in the curcuit and require MORE amperage to keep the correct voltage thus the breaker sees a higher AMPERAGE/CURRENT and fails. So using Ohm's law if V=IR the larger the R(resistance) the larger the I(current or amperage) to maintain V at 115volts.
DON'T use an extention cord between the wall outlet and the welders plug. Plug the welders cord into the wall outlet directly.
You are right that you may also have caused the breaker to weaken and tend to trip more. So replace it.
You've got it wrong again I'm afraid. First, when you add a resistor in series(the cord) it causes a voltage drop farther along the line. So, the voltage is not "maintained", it is reduced at the 1rst posters welder. Reduced voltage at the welder will cause less current not more, just use Ohm's law. It really is kind of illogical to think a welder has the capability to "ask" for more voltage from a wall plug. Secondly, we know adding resistance(the cord) to the line helped the guy's problem so there are a couple of guesses that would be a lot more helpful than removing what helped.
A. Have the first poster check what his line voltage actually is. I see 128vac at my house all the time and that would be a far more likely reason for high inrush currents, per Ohm's law. I've had to redesign the power supplies in all my old tube audio gear that was designed for the 115vac you are presuming to keep them from overheating.
B. The guy might want to call the welders manufacturer after measuring wall voltage to see if there isn't a possible modification to his welder and this is assuming that such a current limiting circuit even excists in his unit.
C. replace the breaker first. It's cheap and can do no harm unless the first guy electrcutes himself.