so I was having this discussion with an old timer and he said in the course of our conversation that ac current has no polarity and another in the talk said well why is so much then made of a wire configuration and I added there is a wall plug tester for the order of the wires in a socket this all came about when adding new input ac 110 v cables to a small 100 amp hobby welder and by industrial standards this is no big unit but on old house wiring and the 50 ft. lead it seems to make a difference as to the grade of wire and how many plugs are on the cord so running two 16 ga. cords side by side one for blk. and one for wht. wired directly to the field coils inside the welder then to the boxes breaker panel works well enough the question it which leg should the switch be i've heard some off brand products can be and are often wired wrong also dose the blk. provide the bulk of the current or the wht. leg as the wht. is the bigger prong on the plug and plug in with a light bulb I can easily dismiss the need for a correct wire hook up as for a amp draw of 20+ amps there seems to be a need for a more closely followed format dosn't the switch spark in side if wired to the load side like in dc or is there really no diff

 

There is no difference between the neutral and live conductor.
What is the Va of the welder, it is important to use the correct size supply cable.
Max.

 

Generally the live hot wire of teh power circuit is what get switched.

And yes the overall gauge equivalent of all the wiring on both the primary and secondary side has a huge effect on the welding capacity and quality of the unit when they are that small.

Although not recommended, using your two 16 ga cords to make an equivalent larger single cord (16 ga x 3 conductor in parallel is just slightly larger than a 12 ga cord) does work and ideally at 50 feet and 20+ amps draw you should be using even larger like a 10 gauge equivalent. Plus if you really need to cheat to get as much amps through as efficiently as possible doing some power factor correction at the welder with a PF capacitor would free up a few more free amps on the supply side as well.

I used to work at a welding supply chain store as the service tech and I was always surprised at how well most small cheap welder could do with a bit of tune up and tweaking to squeeze every watt of power out of them they were capable of. Oversizing the wiring and such and adding PF correction to cut out as much resistive and power factor loses went a long way with the cheapest units.

 

I would use 10 ga. as a minimum & would put switch in black hot lead; white neutral is at ground in switch panel.

 

I have one of those in my basement. Made by Century it is clearly labeled for use on a 30 Amp branch circuit. That said I would carefully read the name plate data on the unit you have. Here in the US that would be a NEMA 5-30P for the plug and a NEMA 5-30R for the receptacle. Additionally the minimum acceptable wire gauge would be AWG 10 and if looking at a long run it would be AWG 8. You would switch the High side. Again this is for the unit I have laying here for 120 VAC service. You wire a switch to make or break the supply conductor-also called the hot lead. The NEC specifically bars switching the grounded (neutral) conductor or the grounding conductor [404.2(B)] (Figure 404-2). Granted in older knob and tube wiring there is no ground but the neutral line is tied to a earth ground at the structure power entry point. Running pairs of AWG 16 I do not see as a good idea and here is why. The cross sectional area of AWG 16 is 1.31 mm^2, the cross sectional area of AWG 10 is 5.26 mm^2. If I double AWG 16 I get 1.31 X 2 = 2.62 mm^2 so you come up pretty short on conductivity. It's aboput the cross sectional area of thew wire and with a 50 foot run I would use AWG 10 - 2. This is just my suggesting and thinking.

<EDIT> and during my slow typing I see everything was covered. </EDIT>

Ron