A household circuit is an electrical system that controls the flow of electricity in a house. It consists of wires that come in from power lines outside and are connected to a fuse and meter. The meters record how much electricity is used and charged for that use of energy. Household circuits are generally wired in parallel, which allows each light or power point to operate independently of the others. The standard U.S. household wiring design has two 120-volt "hot" wires and a neutral wire, which is at ground potential. The two 120-volt wires are obtained by grounding the center tap of the transformer supplying the house so that when one hot wire is swinging positive with respect to ground, the other is swinging negative. This versatile design allows the use of either hot wire to supply the standard 120-volt household circuits. For higher power applications like clothes dryers, electric ranges, air conditioners, etc., both hot wires can be used to produce a 240-volt circuit.

Household circuits contain safety devices called fuses or circuit breakers, which are designed to prevent an excess of electric current entering a house by only allowing a certain maximum current to flow in. When the electrical current is too large, an electromagnet attracts a spring-loaded switch, which breaks the circuit and cuts the power supply. The switch must be reset before any current can flow again. Other safety devices used in household circuits include surge diverters, which protect personal appliances from voltage surges such as those resulting from a lightning strike.

A household circuit consists of three wires: a live wire (red), a neutral wire (black), and an earth wire (green) . The earth wire is used for safety purposes and is connected to metal plates placed in the earth near the house to prevent shock when leakage of charges happens in the metallic body.