Installing 220 / 240 volt Electrical Circuits

Basic 220 Volt Circuits

220 volt circuits (AKA 230 volt, or 240 volt) are used to supply power to appliances which draw high currents such as clothes dryers, ranges, ovens, cook-tops, heaters, air conditioners, rotary phase converters, and water heaters.

Parts of a 220 Circuit

No matter what appliance you are wiring for, any 220 circuit has three elements:

1) The breaker panel connections.

2) The supply wire.

3) The terminal connection, which can be either a special receptacle or a direct connection to an appliance.

Disconnects

For any appliances rated over 300 Volt-Amps (which includes almost everything 220) there must be either a means of disconnect at the appliance or a breaker lock permanently installed in the panel so that a service man can insure his own safety. (NEC article 422.31) "Means of disconnect" can include a pigtail which can be unplugged from a receptacle, a disconnect device (often used for HVAC equipment) or a unit mounted switch which has a clearly labeled off position. Appliances which are in a direct line of site of and in the same room as the breaker panel are exempt from this requirement.
Any time that you are working with aluminum wire, you must coat all connections with conductive grease such as Ideal brand Noalox. Failure to do so will result in a connection failure due to corrosion, and a hazardous condition which could result in fire or electrical shock.

Breaker Panel Connections

Important safety note: Main panels cannot usually be de-energized by turning off breakers. Only qualified personnel should work on main electrical panels. A simple mistake can result in death or injury.
All 220 circuits connect to the breaker panel through a double pole breaker (or equivalent fuse). Double pole breakers often look like a pair of single pole breakers that are stuck together - because that is exactly what they are. 220 equipment will actually function if it is connected by way of two single pole breakers, but it wouldn't be safe or up to code, because in the event of a fault one breaker might trip causing the appliance to stop working, but it would still be energized by the other breaker. So double pole breakers are designed to trip both sides simultaneously. The amp ratings of breakers should never exceed the amp rating of either the wire, appliance, receptacle, or disconnect used in the circuit.

Power Connections

The 2 line voltage wires which are feeding the 220 circuit connect to the double pole breaker in the panel. Both of these wires should be either black or red for their entire exposed length inside of the breaker panel. These wires can be colored with paint, tape, or perm marker to comply with this code.

Ground and Neutral Connections

All modern 220 circuits will also have a ground wire which is identified by either green insulation or by being bare metal with no insulation. The ground wire connects to the ground bar. Some 220 circuits will also have a white insulated neutral wire which connects to the neutral bar, or to the combined neutral / ground bar.

Wire for 220 Circuits

The wire requirements for 220 volt circuits are pretty much the same as for any other circuit - it must be of the proper type for the place that it is being used, it must have sufficient volt - amp capacity, and it must have the correct number of conductors. Proper color coding would also be nice, but isn't a big deal because the exposed lengths of the conductors (in the main panel and in the terminal device) can be colored with paint, tape, or permanent marker. If you are wiring for a dryer, range, or any other 220-110 combo appliance you must use a four conductor wire with an insulated neutral and a separate ground such as X-3-WG. If you are wiring for straight 220 equipment such as a water heater then you can use a three conductor wire such as X-2-WG. The amp rating of the wire should never be less than that of the circuit breaker that is used. You can find a handy wire application / amp rating chart on this page.
Note: You can no longer install 3 wire range or dryer circuits - you must install 4 wire systems for ranges and dryers. If you already have a 3 wire range or dryer then don't worry, your old appliance can be made compatible with a 4 wire system by installing a 4 wire pigtail on it. Then when you buy a new appliance it will plug right in to your new 4 wire system.

Terminal Connections

Connecting the terminal connections on a 220 system aren't all that different than installing any other appliance, fixture or receptacle except that the wire and connection hardware is usually bigger (and a little bit harder to work with) and there is an extra "hot" wire. Because of the bigger stiffer wire it is also more important to cut the conductors to the correct length as you won't be able to stuff extra wire into a box like you can with most fixtures.