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
• Floor area: there's no fixed maximum — one ring per floor is a common practical approach, but large open-plan spaces may need two.
• RCD protection: All socket circuits must be protected by a 30mA RCD or RCBO. Any cable run in a wall must also be on an RCD-protected circuit.
• Spurs: non-fused spurs are permitted, but the total number of spurs must not exceed the number of socket outlets on the ring itself. Each non-fused spur may feed only one single or one twin socket outlet (or one FCU). Spurs may be taken from ring socket terminals or from junction boxes on the ring.

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.