What is the Rated Coil Voltage of a Relay?

The Rated Coil Voltage of a relay is the voltage that the relay is supposed to receive in order to be energized.

This is the voltage that the relay ideally should receive when you energize it. So when designing a relay circuit, you should check its rated coil voltage on the datasheet of the specified relay, and make sure that you design the circuit so that it receives this voltage.

Although the relay may be able to be powered with less voltage, its set (also called operate) voltage, ideally, the relay should receive its rated coil voltage for standard operational use.

Do not use a voltage higher than the rated coil voltage. Too high of a voltage may damage or destroy the magnetic coil, whereas too little voltage may not give it not enough power to actuate. It's best to use a value near or between its rated coil voltage and its operate voltage.