The mains from the Kensington Court Station are laid underground in
a culvert 18 in. by 12 in., which is built with brickwork and cement
under the pavement. A double conductor of flat copper, 0·25 square
inches section, is stretched from shackle insulators attached to iron
bars, which are firmly built into the culvert; the continuity of the
circuit is provided by means of stranded wire, which connects each
section; the flat copper rests on the top of porcelain insulators,
fixed on vertical iron pieces, which are built into the floor.
Connections with the sewers are left for drainage, and six surface
boxes are provided for every hundred yards. Where house connections
have to be made, the branch wires are united by soldering to the bare
copper mains. For crossing under the streets a heavily insulated cable
is employed, and is led through cast-iron pipes.
[Illustration: FIG. 26.]
Until a larger amount of mileage is actually at work, it is difficult
to express an opinion as to which is the cheapest and most efficient
method of laying conductors in the streets. The relative cost of two
plans tried at Kensington Court—the insulated and the bare cable in a
culvert—was given by Mr. Crompton in the following Tables, No. 1 and
No. 2, which are taken from a paper read before the Society of
Telegraph Engineers and Electricians on April 12th, 1888.
Table No. 1 refers more particularly to what is known as the
Callender-Webber system of using bitumen concrete, which is compressed
into blocks or cases usually about 6 ft. long, 8 in. by 5½ in. section,
having two-inch holes through which the insulated copper cable is led.
The estimates given in Table No. 2 were criticised by Mr. Kapp, who
thought that “a more reliable conductor could be obtained by using a
high-class lead-covered cable, which might be laid in the ground with
the simple protection of a rough tarred plank to cover it.” The cost of
digging the trench and running in the cable from the drum was quoted at
3_s._ a yard, and the total cost, inclusive of £10 for surface boxes,
at £155 per 100 yards, instead of £187, as shown by the Table.