The Siemens 3VA9988-0BF23 is a fixed time-delay device in the SENTRON accessories line, purpose-built for the 3VA IEC undervoltage release. It introduces a 100 ms OFF-delay on 24 V DC control power, which means the undervoltage release holds in for that window after the supply drops — enough to ride through a brief sag or transfer without tripping the breaker.
This is a DIN-rail-mounted accessory that clips alongside the 3VA breaker. Its 72.3 mm depth, 44.8 mm width, and 57.5 mm height keep it within the standard SENTRON enclosure footprint — no extra gland-plate space needed for the retrofit.
