Time-lag undervoltage release. This consists in an undervoltage release and an electronic power supply time-lag device outside the circuit-breaker. It enables one to delay opening of the circuit-breaker in the event of a drop in or failure of the power supply to the release itself, with fixed time delays of 0.5, 1, 2, 3 [s] which can be set as desired, thus preventing slow operation due to temporary malfunctions. It can be installed on circuit-breakers S3 - S7, always as an alternative to the opening or undervoltage releases and can only be powered using the dedicated plug-socket connectors. Suitable for installation in 110 V and 220 V circuits with a frequency of 50-60 Hz; the undervoltage release is powered directly by the time-lag device with a rated voltage of 310 V d.c.