How long is the life of a relay if it is continuously energized and used?

Continuous energization may cause the coil, which uses polyurethane copper wire, to generate heat. Since a single wire generally has a heat-resistant life of 40,000 hours, the life will be approximately 5 years when a rated voltage is applied and used in a standard environment.

For more information, see Safty Precautions for All Relays: 1-2 Selecting Relays/Drive Circuits.

For example, when a relay is used in a circuit that is continuously energized for a long period of time without switching operation (emergency light or alarm equipment or error check circuit that releases only when an error occurs and issues an alarm at the b-side contact), a de-energized design is desired.

We have prepared a technical support page dedicated to high-capacity relays that explains in detail "I don't know" when using high-current, high-voltage PCB power relays, such as back EMF voltage (Zener diode and varistor) of the coil, holding voltage application circuit, recommended conditions for high-current substrate flow solder, the influence of magnetic fields, and precautions when connecting in series and parallel. Please also use this as well.
Click here for the high-capacity power relay technical support page.