Because somebody thought it was a good idea. How about a bit more detail about the application? Would that be undercurrent or overcurrent supervision? What's the undervoltage doing?
Depending on the application, Under Voltage Protection may be an electrical code requirement or a safety code requirement, or both.
Canadian Electrical Code.
Undervoltage protection
28-400 Undervoltage protection required for motors (see Appendix B)
Motors shall be disconnected from the source of supply in case of undervoltage by one of the following means,
unless it is evident that no hazard will be incurred through lack of such disconnection:
(a) when automatic restarting is liable to create a hazard, the motor control device shall provide low-voltage
protection; or
(b) when it is necessary or desirable that a motor stop on failure or reduction of voltage and automatically
restart on return of voltage, the motor control device shall provide low-voltage release.
Current supervision.
This is often used to prove that a motor is running. This feature is often found in refrigeration control circuits.
Current above threshold is good. Current below threshold alarms.
Bill
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"Why not the best?"
Jimmy Carter
undervoltage is suppervised by current to prevent a false trip due to a blown pt fuse. If there is a loss of potential but have no change in current the loss of voltage can not be real. So if current remains stable it protects from blown fuse.
