Ring circuit

This article is about a mains power configuration. For circuits where the components are connected in a ring, see ring modulation and phase-locked loop.

"Ring main" redirects here. For the London water infrastructure, see Thames Water Ring Main.

In electricity supply, a ring circuit is an electrical wiring topology in which power is distributed through a continuous cable ring. Each conductor of the ring is connected to the source of the supply at both of its ends. The topology contrasts with the typical radial circuit configuration, in which nodes and the distribution point at the protective device are connected in a line or a line with branches or legs off the main line.

Ring circuits are used in distribution for power and lighting. Rings at the final consumer current draw off point either for power or lighting are known as a ring final circuit. Ring final circuits are often termed by the historical name ring main in the United Kingdom.

Ring circuits are subject to typical cable protection relating for all types of circuit topologies, in which the cable is at a higher amperage loading than the protective device's (breaker) value.

In the United Kingdom there is an anomalous ring final circuit with the cable at a lower amperage loading than the protective device. It is under a waiver, 433.1.204 in British Standards 7671.

Ring final circuits in the United Kingdom splits ring circuits into two types:

1. The 433.1.204 ring final having the cable at a lower maximum amperage rating than the protective device;
2. Ring circuits having the cable at a higher maximum amperage rating than the protective device.