Mains Electricity - Building Wiring

Building Wiring

In most countries, household power is single-phase electric power, with two or three wired contacts at each outlet.

• The live wire (also known as phase, hot or active contact), carries alternating current between the power grid and the household.
• The neutral wire (or 0 (zero)) completes the electrical circuit by also carrying alternating current between the power grid and the household. The neutral is staked into the ground as often as possible, and therefore has the same electrical potential as the earth. This prevents the power circuits from rising beyond earth, such as when they are struck by lightning or become otherwise charged.
• The earth wire or ground connects cases of equipment to earth ground as a protection against faults (Electric Shock).

For more details on this topic, see Ground and neutral.

• Mixed 230V/400V Three-phase electric power (common in northern and central Europe) or 230V single-phase based household wiring

Various earthing systems are used to ensure that the ground and neutral wires have the correct voltages, to prevent shocks when touching grounded objects.

In some installations, there may be two live conductors which carry alternating currents in a three wire single-phase circuit.

Small portable electrical equipment is connected to the power supply through flexible cables terminated in a plug, which is then inserted into a fixed receptacle (socket). Larger household electrical equipment and industrial equipment may be permanently wired to the fixed wiring of the building. For example, in North American homes a window-mounted self-contained air conditioner unit would be connected to a wall plug, whereas the central air conditioning for a whole home would be permanently wired. Larger plug and socket combinations are used for industrial equipment carrying larger currents, higher voltages, or three phase electric power.

Circuit breakers and fuses are used to detect short circuits between the live and neutral wires, or the drawing of more current than the wires are rated to handle to prevent overheating and fire. These protective devices are usually mounted in a central panel in a building, but some wiring systems also provide an over current protection device at the socket or within the plug.

Residual-current devices, also known as ground-fault circuit interrupters and appliance leakage current interrupters, are used to detect ground faults - leakage of current to somewhere other than the neutral and live wires (like the ground wire or a person). When a ground fault is detected, the device quickly cuts off the circuit.