220V House Wiring

220-Volt vs. 110-Volt Electricity

• The two hot wires that come into a residential panel from the transformer on the power line are at 220 volts -- or, more correctly, 240 volts -- relative to each other. Each connects to a bus bar, and most household circuits draw power from one or the other of these bars. Each of these circuits includes a return wire that taps into the transformer, making the voltage between the hot and return wires 110 volts. When you tap 220-volt electricity for a large appliance like a clothes dryer, however, you draw power from both bars.

220-Volt Circuit Breakers

• Circuit breakers are safety devices that snap onto the bus bars and disconnect power when they detect a current that exceeds their rating. A 220-volt circuit requires two breakers, one in contact with each bus bar, and the breakers must connect together so that if one trips, the other does also. This is necessary because a short circuit could occur in one leg of the circuit but not in the other. If only one breaker tripped, the circuit would remain energized and anyone working on it could be electrocuted.

Circuit Rating and Plug Configuration

• The 220-volt circuits power only appliances that consume a large amount of electricity, so their breakers are typically rated for a higher current than those for 110-volt circuits, and the wires have a larger diameter. Although 20-amp 220-volt breakers are available, most 220-volt breakers are rated for 30 amps or more. The minimum cable size is 10-gauge, and 8-gauge cable is required for 50-amp breakers. Plugs are configured according to the amperage rating of the circuit so you can't mistakenly plug a 50-amp appliance into a 30-amp circuit. The National Electrical Manufacturers Association (NEMA) regulates plug configurations.

Making Connections

• All 220-volt cables have two hot wires, one red and one black, and a ground wire. They may also have a white return wire because 220-volt appliances frequently have auxiliary circuits that run on 110-volt power. The 220-volt plugs and appliances have two brass terminals for the hot wires (it doesn't matter to which terminal you connect either wire), a ground terminal and a silver neutral terminal for the white wire. Each hot wire connects to one of the breakers in a paired set; the ground connects to the ground bus bar and the white wire to the neutral bus bar.