The control system for a star delta contactor is
The star contactor and delta contactor are interlocked
relative to each other with a ‘either - or’ condition.
Switching from ‘star’ to ‘delta’ is done automatically
by means of a time relay.
In the circuit above, the star contactor is energised
first, then the mains contactor. Circuits in which the
mains contactor is energised first, followed by the star
contactor, are also common.