Just in case anyone else was confused by this at one time.
General: Installing 220 / 240 volt Electrical Circuits: http://www.nojolt.com/basic-220-circuits.shtml
Frequently asked Question:
Why do some 220 circuits have a neutral wire and others don't?
Also:Because some appliances contain 110 volt internal circuits (such as timers and electronic displays) which require a neutral connection to comply with current codes. When these 4 wire appliances are connected to old 3 wire systems via a 3 wire pigtail they use the ground conductor for the neutral. Other "straight" 220 appliances such as water heaters have no need for a neutral because the current both feeds and returns by way of the two hot wires as the current polarity alternates. Ideally, in any circuit the ground wire serves only as a safety feature and never carries any current under normal circumstances.
Ground and Neutral Connections
Also: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.
Understanding 220 or 240 volt Electrical Circuits
Now for the quick explanation of 240 / 220 volt house current; Appliances which use straight 240 current (such as electric water heaters, or rotary phase converters) also have three wires:
That's it, no neutral. Now, if you are paying attention, then you are probably wondering "If there isn't a neutral wire then how is the circuit completed?" The answer is that when one hot wire is negative, then the other is positive, so the two hot wires complete the circuit together because they are "out of phase". This is why 240 volt circuits connect to double pole breakers that are essentially two single pole breakers tied together. In the main panel, every other breaker is out of phase with the adjoining breakers. So, in essence 240 volt wiring is powered by 2 - 120 volt hot wires that are 180 degrees out of phase.
- A black wire which is often known as the "hot" wire, which carries the current in to the fixture.
- Another "hot" wire which may be blue, red or white (if it is white the code actually requires it to painted or otherwise marked one of the other colors, but often it is not) which also carries current in to the fixture.
- A bare copper wire called the ground, the sole function of which is to enhance user safety.