THE SET UP
I have a 200 amp load center in my cellar. Supply from Con Ed is underground. Inside the load center there are three wires (1/0) coming from Con Ed, one going to one side of the hot bus bar, one to the other, and the third (re-labeled white) going to the neutral bus bar. The neutral bus bar has an insulated wire (looks like a #6) going via EMT to the one inch brass water main about six feet away. The brass water main goes through at least 30 feet of clay soil and drops at least 10 feet (making 20 foot below grade) before connecting to the city's cast iron main. No sneaky plumber has crept in at night and replaced any of the relevant parts with plastic. However, I must get around to jumping the water meter (installed after the load center) one of these days.
There is NO ground bus bar in the load center. None, neant, doesn't exist. This is a total AC system and grounding is via the outside of the cable (or EMT) and the outside of metal boxes including the load center. I can't see without disassembling it but I think the neutral bus bar is connected to the load center electrically. In any event the load center is mounted on a sheet of plywood (so it's somewhat insulated from the wall) and there's a 120V between anywhere on the load center's metal surfaces and either of the live busses. Also between either of the live busses and the neutral bus bar.
All of the above was installed by an expensive licensed master electrician about 25 years ago at the time when the service was upgraded to 200 amp. Con Ed connected their wiring so presumably this is all hunky dorey, in code, and perfectly safe. In any event it's not going to change in my lifetime. Don't even think about suggesting it.
THE ARC WELDER
The main reason for the upgrade to 220V which at the time Con Ed wasn't too happy with (apparently it costs them money and they want to see that they'll recover it quickly) was to install a 30 - 200 amp 220V Sears arc welder. The plug on the end of the arc welder cable is a 90 degree type with a round pin at the top (looks like a piece of tubing cut lengthwise in half so it's not quite round) and two parallel straight pins below. One of the straight pins is longer than the other making one think that it's polarized but I can't see the reason for this.
(I can actually if the US had a REAL 240V system such as I grew up with. In a real 240V system each plug has a hot, neutral, and ground. Between the hot and neutral is 240V; between the hot and ground is 240V; and between the neutral and ground is 0V. There's no such thing as 110 or 120V in the system.)
To plug in the arc welder I installed a black plastic outlet about 6 inches away from the load center, joined to it by a piece of rigid conduit. From the plastic outlet three wires go into the load center, a black to one side of a pair of 40 amp tandem breakers, a red to the other of the pair, and a white to the neutral bus bar. Understand that It was I who decided the round pin should be connected to the neutral bus bar. Even in those days (25 years ago) a round pin looked like a ground but since there's no ground bus bar where was I supposed to put it? Anyway it works fine, doesn't overheat, and as you have doubtless guessed, hasn't electrocuted me or anyone else... yet <g>.
THE TABLE SAW
About ten feet away I have a 10" table saw which used to be a Sears but has been so heavily "breathed on" ( as they used to say in the hot rod business) that they really can't claim ownership any more. The relevant item is that I replaced the motor with a 3hp capacitor-start capacitor-run 220V (actually the name plate says 208V - 250V) Baldor motor. This motor has two and only two terminals--one for the red and one for the black. No green screw or any other color screw that could be a ground. However ground can be achieved via the AC cable which is clamped to the motor. The motor does have some sort of overcurrent protection though, at least I presume that's the function of the red button on the outside. The red button has never operated but it's pretty hard to stall a 3hp motor running a 10" blade even cutting old growth oak or maple.
A 12/2 AC cable with the white relabeled red runs from the motor to a 4 inch metal box mounted underneath the saw. In the 4 inch box is a double pole 20 amp switch and the 12/2 is attached to one end. The other end of the switch has the white (relabeled red) and black from a 12/3 big mother of an extension cord. (Although the extension cord says 12/3 on the outside of the jacket it only has three wires inside: a black, a white, and a green.) The green wire of the extension cord is screwed to the metal box.
The other end of the extension cord has the same plug as the arc welder. The black goes to one of the parallel pins, the white to the other parallel pin, and the green to the round pin. All this works fine, never had a problem, no over-heating, no electrocutions...
But, if I read the other posts around here, what I've done is create a secondary ground for the neutral bus bar. The current could flow back from the neutral bus bar in the load center to the round pin on the outlet then via the green wire of the extension cord to the ground screw of the metal box and then via the outside of the AC to the motor and then to the table saw table itself. Is this analysis about right?
I'm not going to fiddle with the arc welder or its plug, nor am I going to add a ground bus bar in the load center. I suspect the arc welder anticipates that the round pin is a ground and I'm erroneously treating it as a neutral. The real problem here is using a plastic surface mounted outlet. If I put in a metal box and mounted an outlet of the proper configuration (two parallel pins and one round) into the box I could simply connect the round pin to ground and eliminate the white wire to the neutral bus bar. I presume such non-surface-mount outlets exist?
The reason this whole topic arose is that as part of the improvements to the table saw one of the extension wings has been converted into a router table with a router mounted underneath. The router has its own cord and three pin plug which up to now goes into a separate outlet totally independent of the table saw. I was thinking about installing a plug off the table saw switch and eliminating one more cord trailing around my workshop but obviously I can't do this now because I'm either missing a neutral or missing a ground.
Or can I? Just as one can plug a double insulated tool into a three wire grounded outlet (110V) are there outlet configurations for 220V with four pins (hot-hot-neutral-ground) which would allow a no-neutral plug (as I have now) to be inserted? If there were I could leave the arc welder as is and change the extension cord for the table saw to four wire (at enormous expense of course) and have my cake and eat it too. The only other way would be to install two 220V outlets next to the load center, one the 4 pin configuration and the other the present 3 pin. Hmmm, could I install these in the same metal box...? Of course this is a waste as under no conceivable circumstances would the table saw, arc welder, and router ever be used concurrently.
What do you think?