Residential Electrical

Electricity is generated at power plants and transmitted through a network of substations and distribution systems before reaching homes and businesses. Prior to entering a residence, the utility voltage is stepped down by a distribution transformer, typically providing a 120/240-volt single-phase alternating current (AC) service.

At the home, the utility service conductors terminate at the meter. In modern installations, the service first enters an exterior service disconnecting means located outside the building. This disconnect provides a readily accessible means to disconnect power to the entire structure and is required for most new residential installations under current code requirements.

The service consists of three current-carrying conductors: two ungrounded (hot) conductors and one grounded (neutral) conductor. Each hot conductor supplies approximately 120 volts to the neutral conductor, while the voltage between the two hot conductors is approximately 240 volts.

At the service disconnecting means, the grounded (neutral) conductor is bonded to the equipment grounding conductors and the grounding electrode system. This is the single point where the neutral and equipment grounding conductors are connected together. Grounding electrode conductors are connected to approved grounding electrodes such as ground rods, concrete-encased electrodes (Ufer grounds), metal water piping systems, or other electrodes permitted by the NEC.

From the service disconnect, feeders supply the interior distribution panel. In downstream panels, commonly referred to as subpanels, the neutral conductor must remain isolated from equipment grounding conductors. Neutral-to-ground bonding is only permitted at the service disconnecting means.

Inside the electrical panel, branch-circuit overcurrent protective devices distribute power throughout the residence. Modern residential installations commonly utilize:

Standard circuit breakers for overcurrent protection.
AFCI (Arc-Fault Circuit Interrupter) protection to reduce the risk of electrical fires.
GFCI (Ground-Fault Circuit Interrupter) protection to reduce the risk of electric shock.
Dual-function breakers that provide both AFCI and GFCI protection in a single device, simplifying compliance with code requirements in many locations throughout the home.

The NEC also requires a listed Surge Protective Device (SPD) to be installed on dwelling unit services. The SPD helps protect electrical equipment and electronics from transient voltage surges caused by lightning, utility switching operations, and other electrical disturbances.