Triple or Larger Boxes

A ring circuit (more formally a ring final circuit; informally a ring main or just a ring) is an electrical wiring technique that provides two paths for the live, neutral and earth lines by wiring a ring of cable, or sometimes three separate cores in conduit. more...

Home
Car Alarms & Security
Car Amplifiers
Car Audio In-Dash Units
Car CD Changers
Car Electronics
Car Electronics Parts &...
Car GPS Devices
Car Installation Products
Car Portable Appliances
Car Radar, Laser Detectors
Car Signal Processors
Car Speakers & Speaker...
Car Subwoofers & Enclosures
Car Subwoofers
Enclosed Subwoofer Systems
Enclosures
Custom-Fit Boxes
Dual Boxes
Single Boxes
Triple or Larger Boxes
Car Video & Navigation
Other Car Electronics
Wholesale Car Audio Lots

In a single-phase system, the ring starts at the consumer unit (also known as "fuse box" or "breaker box"), visits each socket in turn, and then returns to the consumer unit. In a three-phase system, the ring (which is almost always single-phase) is fed from a single-pole breaker in the distribution board.

The main advantage of a ring circuit is that a cable can be used that has a smaller cross-sectional area than that required for a radial circuit ("straight circuit") of the same current rating. This is because current flows both ways around the ring, thus reducing the current in each wire. Energy losses due to Joule heating depend on the square of the current, so halving the current (for instance) reduces the wasted energy by a factor of four. Thinner copper cable can be used, which is cheaper and easier to work with.

Ring circuits are a British idea and they are commonly used in the United Kingdom and to a lesser extent in the Republic of Ireland. It is likely that they are also used in parts of the Commonwealth of Nations, where Britain had design influence in the past.

The ring main came about because Britain had to embark on a massive rebuilding programme following World War II. There was an acute shortage of copper, and it was necessary to come up with a scheme that used far less copper than would normally be the case. The scheme was specified to use 13 Amp fused socket outlets and several designs for the plugs and sockets appeared. Only the square pin (BS1363) system survives, but the round pin D&S system was still in use in many locations well into the 1980s. This latter plug had the distinctive feature that the fuse was also the live pin and unscrewed from the plug body.

British ring circuits

Ring circuits are commonly used in British wiring with fused 13 A plugs to BS 1363. They are generally wired with 2.5 mm² cable and protected by a 30 A fuse, an older 30 A circuit breaker, or a European harmonised 32 A circuit breaker. Sometimes 4 mm² cable is used if very long cable runs (causing volt drop issues) or derating factors such as thermal insulation are involved. 1.5 mm² Mineral Insulated Copper Clad cable ('pyro') may also be used (as mineral insulated cable can withstand heat more effectively than normal PVC) though obviously more care must be taken with regard to voltage drop on longer runs.

The ring circuit was devised during a time of copper shortage to allow two 3 kW heaters to be used in any two locations and to allow some power to small appliances, and to keep total copper use low. It has stayed the most common circuit configuration in the UK although the 20 A radial (essentially breaking each ring in half and putting the halves on a separate breaker) is becoming more common. Splitting a ring into two 20 A radials can be a useful technique where one leg of the ring is damaged and cannot easily be replaced.

Read more at Wikipedia.org