Originally posted by Nick:
Yes, that's exactly what it is. A closed transition wye-delta starter. Could you expand on the under voltage realy?
There are two general types of low-voltage devices, one of these provides low-voltage release, ie a power failure or a substantial voltage dip interrupts the power flow but does not prevent the reestabliahment of the main circuit when the voltage is restored.
The other is a true undervoltage relay an offers protecction and has to be reset after a power failure.
Timing circuits are often used in this type circuit to help prevent automatic restarting when it is not desired.