6.3.2 - The ring final circuit

The arrangement of a typical ring circuit is shown in {Fig 6.5} and must comply with the following requirements.

Fig 6.5 Ring circuit feeding socket outlets to BS 1363

1. - The floor area served by each ring must not exceed 100 m² for domestic situations, Where ring circuits are used elsewhere (such as in commerce or industry) the diversity must be assessed to ensure that maximum demand will not exceed the rating of the protective device.

2. - Consideration should be given to the provision of a separate ring (or radial) circuit in a kitchen.

3. - Where there is more than one ring circuit in the same building, the installed sockets should be shared approximately evenly between them.

4. - Cable sizes for standard circuits are as follows:

a) p.v.c. insulated cable are 2.5 mm² for live (phase and neutral) conductors and
--- 1.5mm² for the CPC.

b) mineral insulated: 1.5mm²for all conductors.

These sizes assume that sheathed cables are clipped direct, are embedded in plaster, or have one side in contact with thermally insulating material. Single core cables are assumed to be enclosed in conduit or trunking. No allowance has been made for circuits which are bunched, and the ambient temperature is assumed not to exceed 30°C.

5. - The number of unfused spurs fed from the ring circuit must not exceed the number of sockets or fixed appliances connected directly in the ring.

6. - Each non-fused spur may feed no more than one single or one twin socket, or no more than one fixed appliance.

7. - Fixed loads fed by the ring must be locally protected by a fuse of rating no greater than 13 A or by a circuit breaker of maximum rating 16 A.

8. - Fixed equipment such as space heaters, water heaters of capacity greater than 15 litres, and immersion heaters, should not be fed by a ring, but provided with their own circuits.