The 3UG4513-1BR20 from Siemens is a phase monitoring relay. The phase control relay monitors phase sequence, phase failure of one of the three phases and undershoot of at least one line to line voltage of the set nominal line voltage by 20% in a three phase system. The devices are self powered (measuring voltage = rated control supply voltage) and work on the closed-circuit principle. The 3UG4513-1BR20 line monitoring relays monitor all phases of three phase AC networks from 160 to 690V through terminals L1 / L2 / L3 and also draw power from all three phases simultaneously.
