Wiring a plug socket ring main involves connecting a series of sockets in a loop, starting and ending back at the consumer unit.
Understanding the Ring Main
A ring main, or ring circuit, is a wiring configuration commonly used in the UK and some other countries for supplying power to socket outlets. Unlike a radial circuit where cables run out from the consumer unit to sockets in a line (or branches), a ring main forms a complete loop. This design allows current to flow in either direction around the ring, potentially reducing the cable size needed for a given load compared to a radial circuit.
Wiring Steps for a Ring Main
The process primarily involves correctly routing the cable to form the continuous loop. According to the reference:
For flat twin & earth cable, run one leg from the consumer unit to the first socket, then loop between all the required socket outlets. Finally, from the last socket, run the same cable leg back to the consumer to complete the ring circuit.
Here's a breakdown of the steps based on this method:
- Start from the Consumer Unit: Begin by connecting one end of the flat twin & earth cable to the appropriate circuit breaker (typically 32A for a ring main) in the consumer unit. This cable contains three conductors: live (usually brown or red), neutral (usually blue or black), and earth (green and yellow).
- Run to the First Socket: Route this cable from the consumer unit to the location of the first socket outlet on the circuit.
- Loop Between Sockets: At the first socket, the cable conductors are connected to the socket terminals. Then, another piece of flat twin & earth cable is connected to the same terminals in the first socket and run to the next socket outlet. This process is repeated: a cable comes in from the previous socket (or consumer unit for the first one), and another cable goes out to the next socket, with both sets of live, neutral, and earth conductors connected to the respective terminals in each socket. This creates the "looping between all the required socket outlets."
- Complete the Ring Back to the Consumer Unit: From the last socket in the chain, the flat twin & earth cable is run back to the consumer unit. The conductors from this cable are connected to the same terminals in the consumer unit as the cable that started the ring.
This forms the complete ring: Consumer Unit -> Socket 1 -> Socket 2 -> ... -> Last Socket -> Consumer Unit.
Why a Ring Main?
The key advantage of a ring main is that the current drawn by appliances connected to the sockets is shared between the two legs of the ring. This means each leg only carries a portion of the total current, allowing the use of smaller diameter cable (typically 2.5mm² for a 32A ring) than would be required for a radial circuit carrying the same total load (which would typically need 4mm² cable for 32A).
Important Considerations
- All connections must be made securely in the correct terminals (live to live, neutral to neutral, earth to earth) at both the sockets and the consumer unit.
- Safety is paramount. Electrical work should only be undertaken by competent individuals who understand electrical regulations and safety practices. In many regions, significant electrical work like wiring a ring main requires notification to the local authority building control or must be carried out by a registered electrician.
By following the cable routing method described – starting from the consumer unit, looping between sockets, and returning to the consumer unit – you establish the fundamental structure of a plug socket ring main.
