The phase sequence relay for three-phase networks monitors the sequence of phases L1, L2 and L3 as well as the failure of one or more phases. If the phase sequence and voltage (> 183 V) are correct, the output relay(s) is/are closed. If the phase sequence is incorrect or if there is a phase failure (detected as soon as one of the voltages is less than 100 V), the relay opens immediately. If an error is detected when the device is switched on, the relay remains open. Approvals: UL and CSA.