Robert Marino, an electrician from Trumbull, Connecticut, replies:
The short answer is that it depends. Some specifics were left out of your question, but I’ll try to address them in discussing the changeover.
First, I’ll assume that the 220v circuit is a dedicated circuit, which means that it feeds only the 220v receptacle in question and that the cable starts at the electrical panel or subpanel and ends at the 220v receptacle. The changeover will also be slightly different based on whether the 220v receptacle is being fed by a two-wire cable (black and white wires) or a three-wire cable (black, red and white wires).
The existing cable should be 12-ga. or 10-ga. copper cable. If so, then purchase a 20-amp receptacle and a 20-amp single-pole breaker. Before you start, turn off the main breaker for the panel (if the panel has one). Make sure that the 220v breaker at the electrical panel or subpanel is in the off position and that the wires have been disconnected from the breaker. (Note:Working around an electrical panel can be particularly dangerous. If you don’t feel comfortable working around live wires, call in a licensed electrician.) Next, test the 220v receptacle to make sure it’s dead.
Start the changeover at the receptacle end. If the 220v receptacle had been fed by a two-wire cable (a black wire, a white wire and most likely a green or bare ground wire), just connect the white wire (the neutral or grounded conductor) to the silver screw and the black wire (hot or ungrounded conductor) to the brass screw. The ground wire is attached to the box if it’s metal and then to the green screw on the receptacle. I always wrap all my receptacles with electrical tape before reinstalling them.When you’ve finished wiring the new receptacle, mount it back in the box.
If the 220v receptacle was fed by a threewire cable, just cap off the extra red wire with a yellow wire nut and electrical tape. Tuck the wire neatly into the box, and follow the instructions above.
Next, move on to the panel or subpanel. The wires should already have been removed from the old 220v breaker. First, you should connect the white wire to the neutral bar if it isn’t already connected. Remove the old 220v two-pole breaker, and then install the new single-pole breaker with the breaker placed in the off position.
If you are dealing with two wires, simply attach the black (hot) wire to the new breaker. If you’re dealing with three wires, attach the hot wire to the breaker, and again cap off the red wire with a yellow wire nut and electrical tape. Reinstall the panel cover or trim plate, and insert a special filler plate to cover the remaining open space left from the old 220v breaker.
Turn on the main breaker, then the new breaker, and insert an outlet tester into the new outlet. If everything was hooked up properly, the tester should bring you some good news.