Fig. 155.
Fig. 156.
138. Conductors and Insulators. To carry the powerful current from the generating station to distant places where it is to give heat, power, or light, or even to carry the small current of a single cell from one room to another, conductors must be used. To keep the current from passing into the earth before it reaches its destination insulators must be used. The form of conductors and insulators used will depend upon the current and many other conditions. It should be remembered that the current has to be carried to the lamp or motor, through which it passes, and then back again to the dynamo, to form a complete circuit. A break anywhere in the circuit stops the current. Insulators are as important as conductors.
Fig. 157.
Fig. 158.
139. Mains, Service Wires, etc. From the switchboard the current flows out through the streets in large conductors, or mains, the supply being kept up by the dynamos, just as water-pressure is kept up by the constant working of pumps. Branches, called service wires, are led off from the mains to supply houses or factories, one wire leading the current into the house from one main, and a similar one leading it out of the house again to the other main.