Miller 220V spot welder - why does it have 4 wires in its cord?

[metalmagpie]

I picked up a very clean old Miller 220 volt spot welder. It comes connected to a timer box. Everything works very well, but I decided to put a receptacle on the timer box and a plug on the spot welder so I could separate the two, coil up their cords, and put them away more neatly than if they remained connected.

There is nothing at all 3 phase about this system. The timer box plugs into the wall with a 6-15P plug which for sure has 3 conductors. But when I went into the timer box today, new 6-15R in hand, lo and behold the wire that goes from the timer box to the spot welder has 4 leads! Black, white, red and green. And yes, they are all hooked up. Hence my question: why is there a 4th wire powering my spot welder?

There is a schematic, and yes, there are 4 wires, but it's been too long for me and I don't remember enough electronics to figure it out.
http://www.nwnative.us/Grant/p8.pdf

Thanks!

metalmagpie

 

[sfriedberg]

In the schematic, the red wire is pretty obviously the switch control wire ("Push the button, Max! Push the button!") Black and white are supply and neutral/return, and green is ground.

You push the button to start the timed welding cycle. Probably want to have that wire...

[Added in edit] It would be bad form to use a standard NEMA receptacle for mixed power and signal lines. Physically, no problem, but code/AHJ/inspectors would not be happy. And they would be unhappy because it's a safety issue. So I would be really, really careful to permanently label your connectors "Do not connect to standard outlet" or something similar to prevent an accidental frying years from now. The connecting cord, assuming you use appropriate 4-conductor wire, would be a perfectly legit extension. Unless you used male plugs on both ends, in which case it's a "suicide cord" and also bad form.

 

[metalmagpie]

Makes sense, thanks.

I wonder how that connection is made if you take an off-the-shelf standalone spot welder and put it in a pedestal with a standalone timer box. In that case the spot welder would only be fitted with a 3-conductor power cord.

 

[sfriedberg]

If I bought a standalone spot welder, I would expect the timer and the equivalent of the red wire to be totally inside the welder. In particular, while I might mount the standalone welder in a pedestal, I wouldn't expect to wire it to yet another timer.

 

[dana gear]

I picked up a very clean old Miller 220 volt spot welder. It comes connected to a timer box. Everything works very well, but I decided to put a receptacle on the timer box and a plug on the spot welder so I could separate the two, coil up their cords, and put them away more neatly than if they remained connected.

There is nothing at all 3 phase about this system. The timer box plugs into the wall with a 6-15P plug which for sure has 3 conductors. But when I went into the timer box today, new 6-15R in hand, lo and behold the wire that goes from the timer box to the spot welder has 4 leads! Black, white, red and green. And yes, they are all hooked up. Hence my question: why is there a 4th wire powering my spot welder?

There is a schematic, and yes, there are 4 wires, but it's been too long for me and I don't remember enough electronics to figure it out.
http://www.nwnative.us/Grant/p8.pdf

Thanks!

metalmagpie

Keep it simple, use a 4 pole twist lock male on the cord end off the spot and install a female flush twist lock on the timer, as that is the electrical hot end. Use a SO or equivalent cord of the same gauge wire as the spot welders current wiring. Make the dog leg on the twist lock your ground.

 

[metalmagpie]

If I bought a standalone spot welder, I would expect the timer and the equivalent of the red wire to be totally inside the welder. In particular, while I might mount the standalone welder in a pedestal, I wouldn't expect to wire it to yet another timer.

Some standalone spot welders do not have timers at all.

 

[sfriedberg]

Some standalone spot welders do not have timers at all.

Then you would have to add both a switch and the equivalent of the red wire to your pedestal mount to operate such a standalone welder with a standalone timer box (referring back to post #3). In other words, you cannot connect up just the power+ground to the welder and have the timer magically know when it needs to be turned on/off. That's the role of the extra wire in your 4-wire setup.