All 220-volt outlets, regardless of current rating, contain two brass hot terminals and a green ground terminal. Most feature a chrome neutral terminal as well. The black and red hot wires are interchangeable and attach on the brass terminals. The green ground wire attaches to the metal chassis of your house or building. This outlet is used only for safety purposes in case one of the other terminals gets damaged or disconnected.
In addition to the standard 2-wire 120-volt outlets, some houses have 4-wire outlets that can accept both 2-wire and 4-wire appliances. These are usually indicated by a third hot terminal that is not connected to any appliance. The presence of a third hot terminal indicates that it is safe to connect multiple appliances to this outlet. If you attempt to plug in a four-plug appliance into a three-plug outlet, it will get power but also get itself twisted into a knot. You must first convert this outlet from 3 pins to 2 pins to accommodate these extra plugs.
Outlets can be found in almost every room of the house on either side of the wall plate containing the number "3" or "9". They are used primarily to provide a safe ground for sensitive electronics such as computers and hair dryers. However, they are also required by law in all new homes and certain repairs/replacements were made to existing homes to ensure safety.
A 110V outlet (and plug) only has one hot terminal, which is always black. Another significant distinction between 110 and 220 circuits is the wire size. Because 220 volt circuits carry more current, 10 gauge or bigger wire is required, but the average maximum wire size in a 110 volt circuit is 12 gauge.
Because of these differences in voltage and current, any device connected to a 110/220 outlet can be wired in two ways: directly or indirectly. If you connect directly, the device will receive the full voltage of both lines. This could be dangerous if there's a mechanical problem with your appliance; if it's an electrical device, it could be damaged by a high voltage situation. To avoid this problem, devices should not be connected directly to each other or to a panel bus bar. Instead, they must be connected to a switch that connects one line to the other when activated.
Indirect connection through a power controller. Power controllers transform voltage from either line down to the other line's voltage. Thus, they can be used to provide indirect control over appliances that cannot handle direct connection. For example, a power controller can be used to turn off lights when leaving a room or house if they are equipped with motion sensors. The light switches need to be kept in a safe position, so they do not get activated by people walking across the floor. A power controller would keep the lights off until someone turned them back on from another button or switch.
The 220 outlet is bigger and generally spherical, black or dark brown, rather than white. It can contain three or four slots. There is a ground wire on four-slot outlets. One or more of the slots is horizontal or angled. An adapter plug may be required to use a foreign appliance such as a hair dryer or vacuum cleaner in this type of outlet.
The cord itself looks like any other home power cord except it's larger. A typical house current passes through a conductor called "hot" and another called "neutral", both inside the cable sheath. The hot conductor is red in color while the neutral conductor is white or grey. The term "grounding conductor" is also used for the third member of the set, which provides an alternative path for current if there is a problem with the hot or neutral conductors. This third conductor is usually green in color.
The term "two-wire system" refers to the fact that only two conductors are used to carry current; there's no separate conductor for each appliance - just one conductor for all the appliances plugged into the wall socket. A special transformer at the wall box separates out the voltage needed by each appliance. If you have three-wire systems, there's still just one hot conductor, but it carries three currents: one for each appliance plugged in. The third conductor remains neutral though, and is tied together at both ends of the cable.