This chapter shows how the effects of resistance, inductance and capacitance may be applied in an a.c. circuits. The magnetic effect of an inductor has many uses. It is, however, in equipment such as motors and discharge lighting that its effect on the power factor (PF) is substantial enough to cause concern, and makes it necessary to improve the PF. In order to encourage PF improvement, the supply authorities make a higher charge to consumers who do not correct or improve their PF to a suitable level. Capacitors are the most popular method of improving the PF although synchronous motors are used occasionally. PF improvement capacitors may be fitted to individual plant or in banks connected to the supply intake terminals. The first method is more popular as the banked type needs automatic variation as plant is switched on and off.