No_1_June_1962 — Page 70

Socket Outlet Wiring for Houses

An electrical installation needs to be both technically satisfactory and safe and convenient for the user. This Digest (Building Research Station Digest 22) sets out recommendations for the number and placing of socket outlets in smail houses, on the basis of a survey of the occupants' use of electrical appliances. Some technical and economic aspects of the wiring installation are briefly discussed, particularly in relation to the ringcircuit system.

Although this survey was made in Britain, it has lessons for Hong Kong.

THE British Building Research

Station has carried out a survey to see whether the provision of socket outlets in local-authority houses was adequate for the needs of the occupiers. The number of electrical appliances used in a home has greatly increased over the last few years, and in general the number of socket outlets provided has not kept up with this increase. The Station's survey part of its programme on user needs in housing was made to find out how many electrircal ap- pliances were likely to be used in cach room of a house, and where the socket outlets supplying them should best be placed; the actual number of existing socket outlets and their posi- tions were noted, and the occupiers were asked for their opinion of the installation. As a result, it has been possible to make recommendations on the number and positioning of socket outlets in the type of three- bedroom houses most commonly built by local authorities. As against the 6 or 7 outlets usually provided, it is suggested that 15 is a minimum, and 20 a desirable, provision. These recommendations, based on observa- tions of the user's actual needs, agree very closely with recommendations made for post-war housing in 1944, in Post-War Building Studies No. 11.

Altogether, 120 houses were visited in the survey; these had between 6 and 9 socket outlets, wired to a ring circuit.

NUMBER OF OUTLETS

The number of electrical appliances owned by the tenants varied widely, two households having as few as four pieces of equipment and one having twenty-three. In three-quarters of the houses there were between six and fourteen appliances, the average being eleven. Table 1 shows the ap- pliances owned and the rooms which they were used; many of

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these were of course portable and could be used in more than one room,

Electric fires, table lamps, television sets, radios, radiograms or record players, electric irons, vacuum elean- ers and immersion heaters were each found in more than three-quarters of the houses--though not necessarily all in the same houses. Other ap- pliances mentioned were less widely distributed but, in all, 18 different types of equipment were used in one or other of the kitchens, 16 different types of appliance were used in living rooms, and 12 different items were recorded as being used in the bed- rooms. Some houses of course had more than one item of the same kind, e.g. two electric fires or two table lamps, in the same room. The maximum numbers of appliances used at some time in any one room. were 9 for the kitchens, & for living rooms and 6 for the bedrooms.

Not all of the equipment occasion- ally used in a room was likely to be in use at one and the same time. For example, radios and radiograms were unlikely to be used together. Again, for the short time that a vacuum cleaner was in use certain other appliances permanently in the room could, if necessary, be discon- nected without much inconvenience. Electric clocks, of course, should be permanently connected to

a power supply and, although such provision was fairly rare in these houses, the most satisfactory method of doing this is by a suitably fused connector box rather than by one of the general- service socket outlets. Electric cook- ers and immersion heaters were, and should generally be, connected on an independent circuit.

Table 2 has been prepared to show the percentage of people in this study who might be expected to use a cer- tain number of appliances in a room at the same time (excluding vacuum cleaners, clocks, cookers and immer.

sion heaters). It will be seen that, in bedrooms, very few people used more than two appliances at the same time and, even in the main bedroom, the majority used only one or two ap pliances, while 14% used none. În kitchens, on the other hand, there was a much wider use of several appliances at once; in over three- quarters of the kitchens two or more appliances (apart from the cooker) might be used, whilst three or more appliances might be used in about half the kitchens.

The number of connections requir. ed in a room depends on the maxi. mum number of appliances likely to be used simultaneously. If socket outlets to the next whole number above the averages given in Table 2 had been provided in each room, they would have met the require ments in about three-quarters of the living-rooms in this study and in over 90% of the bedrooms. On this basis, minimum recommendations for the number of socket outlets in this type of house can be given (Table 3). The original provision in the houses studied had been considerably less than this, and the installations had, been adapted or modified by two- thirds of the occupants in various ways by using multiple adaptors. by wiring appliances to lighting points, by installing additional socket outlets or by connecting two or more appliances to a single plug. None of the 120 houses had a socket-outlet either in the hall or on the landing, although many tenants said they would have liked to have one there; about a quarter of the tenants in the 80 houses that had an internal store wanted an outlet there, as a connec tion for drills or soldering irons.

The provision recommended in Table 3 would give 15 socket outlets for a 3-bedroom house. This must be considered a minimum. The amount of electrical equipment used is likely to go on increasing and, for instance, the recent report 'Homes for to-day and to-morrow,' publish ed by the British Ministry of Housing and Local Government, recommends 20 socket outlets as a 'desirable pro vision. Some of these could be twin outlet, but in choosing their positions the needs of the user must again he considered.

THE HONG KONG & FAR EAST BUILDER—VOLUME 17, NUMBER 1

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