Final answer:
A voltage-sensing relay is an electrical device that monitors a circuit's voltage and is typically powered by the same circuit it is monitoring. It serves to protect equipment from voltage fluctuations by triggering an on or off switch based on pre-set voltage thresholds.
Step-by-step explanation:
A voltage-sensing relay is an electrical device used to control a circuit based on the voltage of the supply. It is designed to detect over-voltage or under-voltage conditions and is often used to protect motors and other sensitive equipment from voltage fluctuations.
The power source for a voltage-sensing relay is typically the same circuit it is monitoring. For example, if it's installed in a 230V AC electrical circuit, it will typically be powered by that same 230V AC source. This allows the relay to continuously monitor the voltage without the need for an external power source.
These relays are also generally adjustable, allowing the user to set the voltage thresholds at which the relay will switch on or off, thus protecting equipment from potentially damaging electrical conditions.