Wiring a new home workshop

[1_old_man]

No, polarity is not an issue

You may notice that when power comes into your home both hot lines are black. When your breaker box split the 240 power in into two 120 volt lines of breaker positions each side got one of the lines plus the common neutral line, with no regard as to polarity, when each circuit gets down to the receptacle there will just be three wires available. The ground can only go to the ground screw but as to the other two, either wire to either side, makes no difference.

This is about the comment on using a 12 ga, wire in a 50 amp service, or using a 12 ga extension cord for a 30 amp drawing piece of equipment. Here's my comment - what a very bad thing that is to do. It's not silly, it's just plain dumb, and I really don't give a rat's patoot what the Owner's Manual says,it's just plain wrong. And I'm not talking about power losses in the line or its length. Nope, what I mean is that a 12 ga extension cord should not be used to take power to any device that has a power draw of 20 amps or anything even close to that much.

[Broccoli1]

While reading this discussion it occurred to me that when replacing the power cord plug on my MillerMatic 130 after a car parked on it a few months ago, I just simply replaced the plug without paying any attention to polarity of the wires.
I do not use this welder often and it seems to have been acting difficult the last few times I welded with it.
Question is: does it matter which wire goes to which plug blade and if so , how do I determine which wire goes where.
I hope this is not too far off topic but as this is somewhat related I do not want to start a new thread.
Any advice would be appreciated.

YES! IT DOES MATTER on 120v machines like your MM130. It is a safety issue.

The machine really doesn't care though and it shouldn't be causing a problem.

On 120v the white wire terminates on the Silver screw and the Black wire terminates on the Brass screw in the connector.

You can google the "whys" Polarized plug will get you there.