Ring & Radial Final Circuits and Spurs (Lecture Extract)

Vocabulary flashcards covering key terms from the lecture on domestic electrical ring and radial circuits, regulation requirements, and spur arrangements.

Consumer Unit

The main distribution board in a dwelling that houses protective devices and distributes electrical power to final circuits.

Ring Final Circuit

A circuit where the conductors form a closed loop originating and terminating at the consumer unit, supplying socket-outlets along the ring.

Radial Final Circuit

A circuit that starts at the consumer unit and terminates at the last outlet without looping back, supplying outlets in a single line.

Regulation 411.3.3

BS 7671 requirement that socket-outlets accessible to ordinary persons must be protected by additional RCD protection (≤30 mA).

Spur

An extension cable taken from a ring final circuit to supply an additional outlet or accessory.

Non-Fused Spur

A spur connected directly to the ring using the same size cable (typically 2.5 mm²) and allowed to supply one double socket or one fixed load.

Fused Spur / Fused Connection Unit (FCU)

A spur that passes through a fused connection unit containing a 13 A (or lower) fuse, permitting smaller-load circuits such as lighting to be supplied.

2.5 mm² Cable

Standard conductor size used for ring final circuits and non-fused spurs in domestic installations.

13 A Fuse

Standard cartridge fuse value in a fused connection unit that limits the current drawn by the spur to protect downstream cables and equipment.

Circuit Identification

The practice of clearly marking each circuit at the consumer unit so users and electricians know its purpose and limits.

Accessible to Ordinary Persons

Locations in a dwelling where non-qualified occupants can reach electrical equipment; such areas require RCD-protected socket-outlets.

Socket-Outlet

A fixed accessory that provides a point for connecting electrical equipment to the supply, commonly rated at 13 A in UK domestic wiring.

Lighting Circuit Spur

A fused spur taken from a ring circuit, fitted with a 13 A (or suitably reduced) fuse, used to feed lighting points or low-load circuits.

Ring Circuit Cable Looping

Technique where live, neutral, and CPC conductors are looped through each accessory, maintaining continuity around the ring.

Overhead of Ring vs Radial

Although ring circuits can save copper compared with large radial circuits, each circuit must still be separately protected and identified.