Frequency relays switch as a function of the frequency at the input. The relay will energize when a specified starting frequency is exceeded, and it will de-energize when the frequency drops below a specified cut-off or breaking frequency. Thus, these relays can be used to enhance operational safety and reliability. For example, to prevent additional units from starting when the motor does not as yet run at its minimum speed, or to block re-start while the motor is running. Technical features include very low current drain in idle condition and a relay switching capacity of up to 30 A. Coupling to another input signals is available upon request with a view to using the frequency relay for even more complex uses.