of a wiring installation. Permit to workFormal confirmation that electrical wiring is isolated and fully made safe, prior to working on it, required prior to any high voltage works and other high risk activities. Skilled Person (electrically) (formally "Competent Person") defined by BS 7671 as "Person who possesses, as appropriate to the nature of the electrical work to be undertaken, adequate education, training and practical skills, and who is able to perceive risks and avoid hazards which electricity can create". The Electricity at Work Regulations requires persons to be competent to prevent danger and injury. Distribution within premises Consumer unit, consumer control unit, or consumer distribution unit (CU, CDU, CCU; historically and commonly, fuse board/box) Distribution board designed for ordinary low voltage single phase premises, primarily domestic and light commercial wiring. 3-phase power distribution boards are usually known as distribution boards. Distribution board (DB) Panel that splits power from one main source into separate circuits, each with independent protection. Breakers and safety devices Breaker (circuit breaker, CB) Any fixed device that breaks a circuit (that is, while it is drawing current) upon fault condition detection. Miniature circuit breaker (MCB) An overcurrent-protection circuit breaker with standardised current ratings and tripping characteristics, which can be installed in close proximity in consumer units and distribution boards. Residual current device (RCD), also residual current circuit breaker (RCCB) A circuit breaker triggered by unequal currents in live and neutral wires (i.e., electrical power is passing to earth). Mandatory for most circuits as of 17th Edition regulations. Residual current circuit breaker with overcurrent protection (RCBO) Combination of RCD and MCB; breaks circuit on being triggered either as an RCD or by overcurrent. Earth leakage circuit breaker (ELCB) An obsolete circuit breaker type triggered by electrical power in a fault wire connected only to specifically protected parts in the circuit and appliances (i.e., other paths to earth exist). Wires and cables Line (L; formerly, live, or phase) Power-carrying core/wire in a typical low-voltage or domestic installation; colour-coded brown (pre-2004: red). Neutral (N) Power-carrying core/wire in a typical low-voltage or domestic installation, usually bonded to earth (ground) voltage by the supplier; colour-coded blue (pre-2004: black). Earth (E), formally, circuit protective conductor (CPC)Core/wire that provides a connection to earth, for safety and protection purposes, for both end-user devices and metal objects and components in the installation; colour-coded green/yellow striped (may be bare within sheathed cable)(pre-2004: also green/yellow striped, but