Harmony Control. This voltage monitoring relay monitors three-phase supplies for phase failure, as well as the mains voltage for exceeding or falling below an adjustable limit. The neutral conductor is also monitored. The voltage range between phase and neutral conductor is 120-277 VAC. Two relay changeover switches are available for reporting, which can handle up to 5 A. One relay is available for each over- and under-limit reporting. In the event of a phase failure, both relays switch. The two limit values and a switch-off delay are adjustable. The settings are made using controls on the front, which can be protected against changes under a transparent cover. Two LEDs show the status. The device is powered by the measuring voltage. The width is 17.5 mm and it is mounted on a top-hat rail.