What does the simple auto-transformer starter consist of?

The motor is started by connecting its primary to tappings on the starting transformer; then after a time delay, re-connecting direct to the supply. The winding on each limb of the auto-transformer usually has three taps, 60, 75 and 85 per cent of line voltage, but taps to give other percentages may be arranged as required. The auto-transformer may be used in conjunction with a contactor panel, or alternatively a hand-operated switch.

The accompanying illustration shows the wiring diagram of an auto-transformer starter consisting of a line contactor interlocked with a hand-operated change-over switch, three thermal or magnetic overload relays and an auto-transformer.