||04-17-2013 09:59 AM
Your post confuses me now. I have never seen a 220 VAC run with #12 wire. What is the gauge of wire feeding into the disconnect? He told you the line is only 20A ?? Are you setting up what is commonly called an "appliance plug" (not with #12!)? You had better check the installation instructions before finalizing this.
If you are doing an appliace plug, then the picture below would apply. A neutral would be used. But not with #12 wire.
However, the lack of neutral IS how it is done in AC applications where 220 VAC is required. ONLY IF your setup (per instructions) does NOT require a neutral would the following apply.
The bare copper wire is the ground wire which needs to be connected to the green wire in the disconnect. This may be a lug or screw connection depending on the manufacturer. In either case the ground wire is connected in your service panel to the ground buss.
The other two wires supply the 220 VAC. If you use either 10/2 or 8/2 cable you will have a white, black and copper wire in the cable sheath. The white wire should be taped with black tape to designate it as a HOT wire. (This tape flag is done at the main service panel and the disconnect to ensure proper identification) It is NOT a neutral. It will be connected to one of the power lugs in the disconnect. The remaining BLACK wire will be connected to the other power lug.