Which statement best describes an A1 circuit?

• A. Radial circuit, 50 m², 2.5 mm CPC only
• B. Ring circuit, 100 m², 2.5 mm and 1.5 mm CPC, unlimited sockets
• C. Ring circuit, 25 m², 1.0 mm CPC
• D. Radial circuit, 100 m², 4 mm CPC

Answer: (B)

An A1 circuit is a ring final circuit used to supply multiple socket outlets in a domestic installation. The ring format creates a closed loop, allowing current to flow in two directions around the circuit, which gives more outlets and a degree of redundancy. This setup is typically described with a larger area coverage (around 100 m² in typical practice questions) and uses 2.5 mm2 conductors for the live and neutral, with a protective conductor (CPC) of 1.5 mm2. The idea of having “unlimited sockets” reflects the ring’s ability to feed many outlets along the circuit, unlike a radial circuit that has a single path from the origin to its loads and a more limited number of outlets.

So the option describing a ring circuit, about 100 m², with 2.5 mm2 live/neutral and a 1.5 mm2 CPC, and effectively unlimited sockets, best matches what an A1 circuit is. The other choices describe radial layouts or use inappropriate sizes or area limits for an A1 ring final circuit.