New Shop Wiring
Well, I'm finally getting around to adding some additional circuits to the detached garage in my new home. The previous owners built the garage in 2003 and had it wired at the time with a large sub panel (100A) and ran some lighting circuits, 120V outlets, and one 120/240 welding outlet. Previous work was done by an lic'd electrician. I'm adding a few more circuits and have some questions about what they did and what I'm about to do.
1) Their welding circuit consists of 12-3 wire running to the sub panel. At the subpanel each hot (red and black) received an individual 20AMP single pole breaker. This would allow one hot leg or the other (or both) to be off or on. Also if one leg trips, the other wouldn't. I can't figure out why you would want to do this. No recepticle is installed at the outlet box, all wire ends are capped with wire nuts and taped. (They built this garage and then never used it for anything)
2) I'm adding two 4000W electric element heaters. They each draw 17A and each requires their own dedicated circuit with a 20AMP breaker and a NEMA 6-20 outlet. This is a hot-hot-ground configuration. I've run 10-3 wire incase I ever desire to upgrade to a 5000W (22A) heaters, the additional wire capacity will let me swap to a 30A outlet along with a 30A breaker without having to redo the work behind the wall. Is there anything wrong with using the larger capacity wire than necessary on these two circuits?
3A) The use of hot-hot-grnd on 240V circuits baffles me a little. Since I'm using 8-3 on a 40A breaker for my compressor (5HP motor, plate amperage is 22A) why exactly don't I use the neutral wire at all? Compressor plug is hot-hot-grnd, can't remember what NEMA type it is.
3B) Basically same question for the two electric heating units. The NEMA 6-20 plugs are hot-hot-grnd. All of the advice I've seen here and other places says to cap the neutral in the outlet box and disconnect & cap the neutral at the sub panel in a scenario like this.
I always thought the neutral wire is what carried my "spent" electricity back to the source - so it was somewhat integral in getting a circuit to function (a closed loop if you will). On these 240V setups is the bare ground wire actually carrying the spent electricity?