Circuit breaker (1) – A type of protective device for circuits, it will protect a circuit from overload and fault currents.

Fuse (2) – A fuse is a protective device. They are designed so that when more current is drawn through them than they are designed to take, a part of it melts, causing the circuit to become open and the electricity supply to become disconnected.

RCD – Residual Current Device, this is a type of device used to disconnect the electrical supply to a circuit, or bank of circuits in the event of a fault from line to earth. It does this by essentially monitoring the line and neutral currents. If there was a fault between line and earth, the RCD would trip as there would be no current on the neutral conductor. There are three commonly encountered types:

• RCCB (3) – Residual Current Circuit Breaker, what most people commonly refer to as an ‘RCD’, will often be found in a consumer unit protecting a bank of circuits.
• RCBO (4) – Residual Current Circuit Breaker with Overload protection, this combines the function of an RCD and a circuit breaker in one device and can be found protecting one circuit.
• SRCD – Socket Residual Current Device, as the name suggests this type of RCD is integral to a socket outlet.

SPD – Surge Protection Device, these are devices designed to limit a sudden surge of electrical energy known as a transient over-voltage.

Main switch (5) – Although not a protective device, in a typical household, the mains switch is located in the consumer unit. Its purpose is to disconnect the supply of electricity to the installation.