| Can anyone tell me what sizes of ROMEX wire I should run for the | following circuits?
I'll assume the listed amperages are the circuit specifications, and the actual load of the equipment is 80% of that. If this is wrong, please post an update. All wiring is copper only.
| A. 240V, 20A (table saw OR compressor but never both) with a run of | maybe 18' from the subpanel
AWG 12. Use a single NEMA 6-20R receptacle.
| B. 240V, 20A (18" bandsaw or 12" planer/molder) with a run of maybe 20' | from the subpanel.
AWG 12. Use a single NEMA 6-20R receptacle.
| C. 240V, 50A (arc welder) with a run of maybe 1 foot from the subpanel.
Some will say you can use AWG 8 and you probably can, if it has a high enough temperature rating (75C or more). Personally I'd run AWG 6 to this. For just one foot, you're not saving all that much to go with AWG 8.
An arc welder will not need a neutral. However, some may come with a NEMA 14-50P plug instead of a NEMA 6-50P plug. Check what yours has and choose the matching receptacle. If you do install a 14-50R outlet you must run the neutral wire to it and connect it correctly. However, if you can use a 6-50R outlet, you can omit the neutral as described.
As close to the panel that the arc welder will be, the choice does not really matter. On one hand you save a few pennies without a neutral. But if you later need a combination 120/240 for some reason at that location, you can just run another circuit.
All 240 volt circuits that do not need a neutral can be wired without one, as long as a NEMA 6-XXR outlet is involved. Or you can choose to go ahead and wire the circuit with a neutral in case you might ever decide it may need 120 volts in the future.
To wire the circuit for 240 with a neutral for 120 volts, you would use a 4 wire cable that has a ground wire, a white wire (neutral), a black wire (one hot), and a red wire (other hot). Your electrician should connect the neutral at the panel and leave it long and capped off at the outlet.
To wire the circuit for 240 without a neutral, you would use a 3 wire cable that has a ground wire, a white wire (normally used as neutral but we'll change that), and a black wire. Buy some red electrical tape (black can be used, but red is better) appropriate for marking (most is). The white wire will be wrapped several times around for 2 to 4 inches of its length at each end with the red tape to re-designate it as a hot wire. If there are any junctions, mark the wire at those junctions, too.
If you insert a switch in a 240 volt circuit, use a TWO POLE switch so it breaks the circuit on BOTH hot wires. If you use a neutral, do not switch the neutral.
If this is a wet environment, you may need to use UF cable instead of NM cable. Be sure the wiring is placed where it will avoid any possible damage from mechanical accidents. If the wiring is in conduit, you can use singles wires, THHN, or if a wet environment, THWN.