When use undervoltage release?

Under voltage protection (release?) is used in industry. If there was a power failure and a piece of equipment was running when the failure occurred for safety reasons the machinery should not start up on its own when the power returns back on. With under voltage protection the operator restarts the machinery after checking that there is no danger to anyone and the machine is clear to start. To obtain this safety feature an electrical contactor is used in conjunction with remote stop - start buttons located at the machine the operator is working.