to outlets being placed near the mid- dle of bedroom walls, where they were likely to be obstructed by furni ture. In placing socket outlets in bedrooms, it may also be possible to give consideration to using them as points for spur connections to other parts of the house.
For the convenience and safety of the user, it is as important to place the socket outlets where they are needed as to provide a sufficient number. As it happens. the num ber of outlet positions suggested to give adequate coverage to the rooms is about the same as the minimum number of outlets recommended in Table 3 on the basis of the number of connections the occupants might wish to make. Figure 2 shows the plan of one of the house types in cluded in the survey, with position of outlets actually provided and the positions recommended minimum; it should perhaps he noted, however. that this particular plan shows one, but not necessarily the only, satisfactory minimum ar- rangement.
as
a
The minimum provision can be increased at relatively little extra cost by installing twin socket out- lets at selected positions; alterna- tipely, suitably fused adaptors can be used to increase the number of connections. although this is not so satisfactory. Such increased provi- sion will be considered further be- low.
The height at which outlets were placed did not seem to be a matter of much concern to the occupants of the houses studied; most of them were satisfied with the heights they happened to have. These about 3 ft. 6 in. in all kitchens and in some living rooms, and at skirt- ing height (9-12 in.) in other living rooms and in the bedrooms.
RING-CIRCUIT WIRING
were
The ring-circuit system, by now airly widely used, makes for great- er convenience to the user, and greater economy, than the tradition- l wiring arrangement, in which ach socket outlet requires an in- dividual sub-circuit with its able-run from a separate fuse-way. n a ring-circuit, a number of out- ets is served by a loop of cable run
own
current
which forms one sub-circuit; each of the pair of conductors forming the loop starts from and returns to a single terminal on the fuse distri bution board. Since each outlet on the ring receives current from two directions. the effective carrying capacity of the cable is greater than in the traditional sys. tem; in addition, of course, the ring. circuit needs a shorter total length of cable. The ring system offers a further simplification in that single standard size of socket outlet and plug has been developed for use with it; fused plugs are used, so that any portable appliance, pro- tected by its appropriate fuse. can be plugged into any socket.
a
In houses or flats, any number of 13-A outlets may be served by a single ring circuit. within a floor area of 1000 ft2: in larger houses, where there is more than one ring circuit. the outlets must be reason- ably distributed between the cir cuits.* "Spur connections may be taken from the ring circuit to serve outlying socket-outlets; only two socket-outlets or one fixed appliance may be fed from each spur. and not more than half of all the points in- stalled may be fed by spurs. The maximum rating of the fuse pro- tecting a ring circuit is 30-A; there is no restriction on the number of outlets installed in such a circuit in houses or flats because of the load diversity in the installation that is to say. since not all appliances are switched on at once. the total demand for power at any one time is very unlikely to exceed the 30-A rating. Cookers and immersion hearts should be wired on separate circuits.
With this kind of circuit it is of course relatively easy to install additional outlets where they are needed; the circuit can be designed to meet the user's expected needs, and the possibility of adding spurs, within the limits mentioned. also makes for greater flexibility.
With this kind of circuit it is of course relatively easy to install ad- ditional outlets where they are needed; the circuit can be designed to meet the user's expected needs.
**
INSTITUTION ENGINEERS:
OF ELECTRICAL
Regulations for the electrical equip- ment of buildings (13th edition).
THE HONG KONG & FAR EAST BUILDER-VOLUME 17, NUMBER 1
and the pissibility of adding spurs. within the limits mentioned, also makes for greater flexibility.
Some of these points are illustrat- ed in Fig. 3, which shows the ring circuit for the socket-outlet installa. tion suggested in Fig. 2. For in- stance. less than half the total num- ber of points are fed by spurs. A spur from bedroom 1 serves two outlets installed back-to-back in the living room and dining-room; if further outlets were required here. it would be necessary either to ex tend the ring to this part of the house or to install another spur. This example also shows that some extra cost may have to be accepted to ensure a convenient installation; placing a socket outlet near the sink in the kitchen has entailed rather a long spur from bedroom 2.
Clearly, it is not possible, if the installation is to be satisfactory to the user. to reduce the length of wiring unduly. However, some economies are possible in the in- stallation of the outlets themselves. It must be realised, though, that the client will only benefit from such economies if a realistic system of charging is adopted. based on ac tual costs, in place of the common system of making a fixed charge per socket outlet.
For example. twin' socket-outlet boxes are available, which can be bought at little more cost than sin- gle boxes, and where such a twin outlet replaces a single outlet, the bet additional cost is about 12s. If two outlets are installed back-to back on either side of a wall, again using a single box, the cost of the addition is about 17s. 6d., whilst for three outlets (twin outlets back to-back with a single outlet) the cost for the two additions is about £1 10s. (These additional costs are, of course, independent of the basic cost of wiring to and installing the first outlet. which will depend on the position of the outlet as well as on labour and other costs. The net cost of a twin socket outlet is not only less than that of two single outlets but less than that of one outlet and a fused multiple adaptor; where several appliances are likely to be used in any part of the house, therefore, the installation of twin outlets should considered.
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