Monitoring relays detect changes in operational or environmental conditions and protect downstream equipment from damage. Current-monitoring relays detect whether current flowing through circuits is over or under its set threshold. Voltage-monitoring relays detect whether voltage flowing through circuits is outside its set threshold. Phase-monitoring relays monitor single-phase and three-phase systems to detect abnormalities with phase. Liquid-level monitoring relays measure conductive fluids inside tanks and vessels for mixing and filling applications. Seal-leakage monitoring relays detect leaks and overheating of submersible pumps. Temperature-monitoring relays measure the temperature of gases, liquids, and surfaces. Frequency-monitoring relays detect whether the frequency of an AC power source is outside its set threshold. Speed-monitoring relays detect whether the movement or speed of a motor, machine, or system is outside its set threshold.