Socket Outlets

Socket Outlets Points : Socket Outlets, Details of System, Correct sizes wire, Planning the Layout, Socket Outlets Few years ago, there were far too many plugs and sockets of different sizes and shapes, and often three or four types were installed in one house. In view of these difficulties, and in order to keep the cost of wiring as low as possible consistent with safety, it was decided to standardize on a 13 amp socket outlet with a plug which was fused to the appropriate rating of the appliance to which it was connected. Thus one 13 amp socket outlet could supply a 3 kW fire, with a plug fused at 13 amp, and another 13 amp socket outlet could supply a table lamp, with a plug fused at 2 amp. Since these socket outlets could be used’ for any load up to 13 amp, they were generally arranged at intervals round a room, with the two current carrying conductors looped from one socket to the next, and both ends of the circuit being connected to a single fuse or circuit breaker. This type of circuit is known as a ring circuit.

The advantages of this system are that a confusing array of sizes and shapes is brought down to one. Any appliance with a loading sizes and shapes is brought down to one, any appliance with a loading not greater than 3 kW (at 230 V) can be connected with perfect safety to any socket, and that under certain conditions, an unlimited number of socket outlets may be wired on one circuit. Also if a fault occurs on a lamp, flexible cord or other appliance which results in a short on a lamp, flexible cord or other appliance which results in a short circuit or overload, the local fuse in the plug will blow and the other socket outlets will not be affected. It is then an easy matter to locate and replace this fuse.

Since any type of appliance, whether lighting or power, can be connected to any socket outlet, then unless the electricity company can charge a single tariff, the system would not be very economical. However, with intelligent use, this system can be much cheaper and very convenient to the user. It is recommended for use in commercial and industrial premises, hospitals, schools, shops and ‘public buildings. Details of System The three pins of the plug and the corresponding holes in the socket are rectangular in shape. In each plug there is a recess for the cartridge type fuse. These are rated at 2, 5, 10 and 13 amp. The flexible cord connected to a fused plug must be of the correct size so that the fuse protects the cord. Correct sizes are 2 amp fuse — not smaller than 14/.0076
5 amp fuse — not smaller than 231.0076
10 am fuse — not smaller than 401.0076
13 am fuse — not smaller than 701.0076
Generally the socket outlet is either of the shuttered un switched type, the shuttered switched type, or plain switched type.

Planning the Layout The object should be to provide socket outlets in all positions where table and standard lamps, fans, irons and other appliances are likely to be required, so as to avoid the use of plug adaptors and long dangling flexible cords. The general principle is to estimate the number of outlets required and then add a further 20% as these are bound to be needed later.

Once the number has been obtained, the anticipated maximum load had to be estimated. If this exceeds 30 amps, the socket outlets should be wired on more than one 30 amp circuit, but if it is not likely to exceed 30 amps, then one circuit comprising ten socket outlets is usually sufficient. Depending on requirements quite a large diversity factor can be applied with these socket outlets, especially in houses or flats, and the table in Fig. gives a guide.

Although a ring circuit is generally run right around room, or small building, there are some remote positions where to run the ring would merely waste cable. For this reason, the process of “spurring off” can be used, where lead are taken from the nearest socket outlet and run off to the desired position. Each spur however of socket outlets fed by spurs from any one ring circuits must not of socket outlets fed by spurs from any one ring circuit must not exceed 50% of the total number of socket outlets connected to the circuit. When fixed appliances such as water heaters, boilers and inset electric fires are installed, .they may be connected to ring or other 13 amp socket outlet circuits, if they are protected by local fuses. However, the total loading of these appliances on any one circuit must not exceed 15 amps, and the number of fixed appliances must be allowed for when deciding upon the maximum number of socket outlets which may be connected to the circuit.