Loop circuits connect each phase or line through multiple outlets back to the same fuse or circuit breaker. It originated in the UK after WWII to save copper and labor. It allows for unlimited outlets but has low overcurrent tolerance and difficulty finding faults.
A loop circuit is a power distribution wiring method that sees each phase or line connected from one point to another through a number of outlets and ultimately back on the same fuse, circuit breaker or bus connector from which it originated . The loop circuit is most commonly used for wiring single-phase installation, but can also be found in three-phase power supplies. Also known as ring master or loop power, the loop circuit originated in the UK in response to the severe copper shortage experienced after the Second World War. This method of wiring allowed smaller quantities of lighter gauge wire to be used and also saved on labor. In the ring circuits it is possible to insert an unlimited number of points of sale with the only limitation of the total area served.
Conventional domestic radial circuit wiring consists of live, neutral and earth lines which are fed from the consumer unit (CU) or distribution board (DB) to a number of outlets. Once these lines reach the outlets, they are simply bridged from one to the other until all outlets have an active neutral and earth connection. The total number of outlets on any given circuit depends on the capacity of the circuit breaker or fuse they come from and their cumulative amperages. Loop circuit wiring, on the other hand, has live, neutral, and ground lines that are fed to a number of outlets and then fed back to the originating circuit breaker or fuse, thus forming an uninterrupted loop.
This style of wiring originated in Britain in response to calls to save copper usage due to severe shortages of the metal after World War II. Wiring home circuits in this way offered the benefit of lighter wiring requirements and significant labor savings. Having house circuits wired in a loop also meant that if one “leg” of the loop failed, the other would still be able to carry a good deal of the load. At the same time, the older, rounder plugs were replaced with flat, fuse-top pin types that required less copper to manufacture.
In most domestic installations it was, and still is, the common practice to wire each floor of the building on its own loop circuit and with the kitchen on a separate circuit. While radial circuits have a finite number of outlets they can support, ring circuits can power any number of outlets with the only constraint being the total area fed by the circuit which is generally 100 m2 (1076 sq ft) . If additional outlets are needed on an existing ring circuit, the new additions are typically added by installing a “spur,” which is simply a parallel extension from the closest existing outlet. One of the disadvantages of loop circuits is their low overcurrent tolerance and the difficulty of finding faults and balancing loads correctly. The multiple number of outlets involved also means that ring powered switches are usually large and average 30-32 amps.
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