5.—Grease and dirt must be scrupulously avoided.
Great care is absolutely necessary in making junctions, as they are the principal sources of defect in the insulation of electrical submarine cables.
Junction Boxes.—When it is necessary to employ a multiple cable, a junction box is used to facilitate the connection of the several separate wires diverging from the extremities of such a cable. In one angle of such a box the multiple cable is introduced, while the separate cables make their exit on the opposite sides and pass to the different mines. Different views of a junction box are shown at [Fig. 41], where A is a plan of the top or lid, B a plan of the bottom, with the lid off, C an elevation, and D a section of the box.
The manner of using the junction box is as follows:—
The multiple cable is put in at a, and secured there by means of a nipping hook, shown at [Fig. 42], which hook passes through the bottom of the junction and is made secure by means of a nut. The single core cables radiating from the junction box pass through the openings b, b, b on the sides, and angle opposite to where the multiple cable a enters. Each multiple cable is composed of seven cores, and each of these is connected by means of joints with the mine cables within the junction box, and each of these seven cables is secured by means of a nipper similar to, but smaller than, the one shown at [Fig. 42], which are also secured by means of nuts, as in the case of the multiple cable nipping hook. When all the connections are made, the lid A is placed so as to rest on the studs c, c, c, and firmly secured by a bolt d, which is made water-tight by means of a washer and nut.
By means of the nipping hooks, which take any strain that may be brought on the cables, the connections within the box are ensured against injury by such a cause.
To enable the whole to be lifted together for the purposes of examination of the cables, &c., a buoyed rope is connected to the eye-bolt e. For this service a dummy circuit closer is the best form of buoy, it having great buoyancy and resembling in appearance an active circuit closer.
A junction box should be placed in such a position as to be easily attained, even in the presence of an enemy, and its buoy should, if possible, not be seen. It is also very essential that it should be in a safe and guarded position, for any injury to the junction box or multiple cable would be fatal to the group of mines in connection.
In the following cases, special junction boxes are used:—
1.—A seven cored armoured cable to be connected direct to another length of the same.