The Siemens 3VA9978-0BF22 is a SENTRON time-delay accessory designed specifically for use with 3VA undervoltage releases. It introduces a fixed OFF-delay of at least 100 ms when powered at 230 V AC, which means the undervoltage release holds in for that window after control power drops — enough to ride through a brief sag or transfer without dropping the main breaker.
This module mounts as an add-on to the 3VA undervoltage release, not as a standalone panel component. The physical envelope — 72.3 mm deep, 44.8 mm wide, 57.5 mm high — fits within the breaker's accessory footprint, so no additional DIN rail space is consumed. Wire termination accepts a stripped length of 10 mm (0.4 in).