The Siemens 3VA9978-0BD12 is a SENTRON universal auxiliary release designed for the 3VA4, 3VA5, and 3VA6 series of molded-case circuit breakers. It operates on a 24V DC control supply, drawing up to 20 W at maximum DC load. This is the part that trips the breaker remotely — think emergency-stop circuits, undervoltage protection schemes, or PLC-driven shunt-trip commands from a safety relay. Physically, it occupies three slots in the breaker's accessory bay, with a footprint of 25.7 mm wide by 65.1 mm tall by 28.8 mm deep. The auxiliary circuit connection accepts AWG18 wire with a 10 mm (0.4 in) strip length — standard for panel wiring.
The surge voltage resistance of 4 kV and the overvoltage category III rating align with IEC 60947-2 requirements for breaker accessories in industrial installations. If your panel is specified around 3VA4/5/6 breakers, this release drops in without modification — no adapter plate, no wiring harness change.
A 24 VDC supply feeding this release needs to deliver at least 0.83 A continuously to hold the coil energized; inrush at pickup will be higher. Factor that into your DC load budget — especially if the same supply also feeds PLC outputs or safety relays. Overvoltage category III confirms it's suitable for fixed-installation distribution panels, not just downstream equipment. Together, these two ratings tell the panel builder this release is built for the same environment as the breaker it mounts in.