Ring Final Circuits

A ring final circuit is the standard way to wire socket outlets in UK homes. Unlike a simple radial (single-ended) run, the cable forms a complete ring — starting at the consumer unit, looping around all the sockets, and returning to the same MCB.

The Ring

Why a Ring?

The ring gives each socket two paths back to the MCB — current can flow either way around the ring. This halves the effective resistance and allows a 32A MCB to protect 2.5mm² cable that could otherwise only carry ~20A on a radial.

Rules for Ring Final Circuits (BS 7671)

• Cable: 2.5mm² T&E (post-2006 colours: brown/blue/earth)
• MCB: 32A
• Max floor area: unlimited in theory, but practically one ring per floor
• Spurs: permitted, one spur per socket on the ring, one socket per spur

Checking a Ring

An electrician will verify a ring using the end-to-end resistance test (R1+R2): each conductor is looped at the far end and resistance measured at the CU. A balanced ring gives equal readings at every socket.