than BS 1363 sockets are connected to a ring circuit or it is desired to place more than one socket for low power equipment on a spur, a BS 1363 fused connection unit (FCU) is used. In the case of fixed appliances this will be a switched fused connection unit (SFCU) to provide a point of isolation for the appliance, but in other cases such as feeding multiple lighting points (putting lighting on a ring though is generally considered bad practice in new installation but is often done when adding lights to an existing property) or multiple sockets, an unswitched one is often preferable. Fixed appliances with a power rating of 3 kW or more (for example, water heaters and some electric cookers) or with a non-trivial power demand for long periods (for example, immersion heaters) may be connected to a ring circuit, but it is strongly recommended that instead they are connected to their own dedicated circuit. However, there are plenty of older installations with such loads on a ring circuit. Advantages Proponents of the ring circuit point out that, when correctly installed, there are also a number of advantages to be considered. Area served For rooms that are square or circular, a ring circuit can deliver more power per unit of floor area for a given cable size than a simple radial circuit, and the source impedance and therefore voltage drop to the furthest point is lower. Alternatively, to deliver the same power to the same building with radial circuits would require more final circuits or a heavier cable. High integrity earthing As all fittings on the ring are earthed from both sides, two independent faults are needed to create an 'off earth' fault. Continuous continuity verification from any point The continuity of each conductor right round all the points on the ring can be verified from any point, and if this needs to be done as part of live installation monitoring, it can be verified by current clamp injection with the system energised. Criticism The ring final circuit concept has been criticized in a number of ways compared to radials, and some of these concerns could explain the lack of widespread adoption outside the United Kingdom. Fault conditions are not apparent when in use Ring circuits may continue to operate without the user being aware of any problem if there are certain types of fault condition or