In jointing up seven-strand electric cables, the insulating covering is removed for several inches from each of the two ends to be joined, and the copper surfaces are scraped absolutely clean. They should be touched as little as possible by the hands to prevent any moisture reaching them. Tinned wire is preferable. Care must be taken that nicks are not made in the strands while the insulator is being removed, since such nicks decrease the sectional area of the wire to a considerable extent. The wires are then taken and opened out, the two sets being placed together and interlinked, the central strand of a seven-strand cable being cut off short to allow this to be done. The ends are then well wrapped round each other, and trimmed over fairly smooth with pliers. Using resin as a flux, and taking care throughout the whole operation that everything is clean, the whole is then well soldered. The insulation on the cable will determine whether strips of pure rubber or of gutta-percha should be then wound round the joint. The latter should be warmed by a spirit-lamp and well kneaded by thumb and lingers.

After several layers of this strip have been applied, the whole is wound round with specially prepared tape.