The Siemens 3VA9877-0GX31 is a SENTRON auxiliary switch module — one auxiliary switch, OFF to ON — designed as a field-installable accessory for the 3VA57/3VA58/3VA59 and 3VA67/3VA68/3VA69 families of molded-case circuit breakers. It mounts inside the breaker's rotary operator mechanism, not on a separate DIN rail, so the panel layout stays unchanged when you add it.
The thermal current rating of 5 A (Ith) sets the continuous carry limit through the auxiliary contacts — adequate for signaling a PLC input or a contactor coil, not for powering a load directly. Switching capability is defined per utilization category across the voltage range. In AC-12 (resistive loads like pilot lamps and relays) it switches 5 A from 12 V up to 240 V. In AC-15 (solenoid and contactor coils) it switches 2 A across the same voltage range. For DC-13 (solenoid valves, DC contactors) it switches 0.2 A at 12 V through 250 V — the same 0.2 A limit holds at 110 V and 250 V DC, so verify your DC load current stays under that ceiling. Surge voltage resistance of 4 kV matches the impulse withstand expected in a 400 V distribution panel.