Construction of Telegraph Cables

1. Conductor Conductors varied from single core (one length of wire) to multi core (many lengths wound together) and were usually made from copper, since it had a low resistance. 2. Insulation The insulating layer was invariably made from commercial gutta, a mixture of the gum gutta-percha (which was shipped in from the Far East) resin and water. Good quality gutta was tough, water resistant and durable. 3. Jute Yarn The yarn acted as a cushion between the cable core and the heavy iron wires that were used to protect it. 4. Inner Sheathing Whereas the gutta-percha provided electrical insulation, the inner sheathing of iron cables provided mechanical insulation, protecting the core from being damaged. For deep water, the breaking strain of the iron cables had to be around 100 tons per square inch. 5. Jute and Compound The inner sheathing was covered in 2 layers of conversely wrapped jute yarn, in order to keep the iron cables together. 6. Outer Sheath The part of the cable that was out of the water at the Shore End was more prone to damage, so it was sheathed in a second layer of iron for added protection from the elements. 7. Outer Jute Yarn and Compound To keep the outer sheathing together, the iron cables were wrapped in Jute Yarn.

Coating the cables with Gutta Percha. This is a machine that automated the process of covering copper wire with gutta percha.