The Siemens 3VA9978-0AA12 is a SENTRON auxiliary switch with changeover contacts (type HQ, 7 mm contact gap) designed as an accessory for 3VA4, 3VA5, and 3VA6 molded-case circuit breakers. It provides remote status indication — open, closed, or tripped — from the breaker's internal mechanism. The thermal current rating of 6 A sets the continuous-carry capacity through the contacts; the actual switching capability depends on the load type and voltage, defined by the utilization categories.
For AC control circuits, the switch handles 6 A at 12–240 V under AC-12 duty (resistive loads like pilot lights and relays), and 3 A under AC-15 duty (solenoid valves and contactor coils — the inductive inrush matters). For DC control circuits, DC-12 (resistive) is rated 6 A at 12 V, 4 A at 24 V, 2 A at 48 V; DC-13 (solenoid with significant inductance) drops to 1 A at 12 V, 0.8 A at 24 V, and 0.4 A at 48 V. The DC-13 ratings are the limiting factor for any DC coil or valve: at 24 VDC, the switch can interrupt 0.8 A, so verify the load's inrush and holding current against that ceiling.
This auxiliary switch clips into the accessory slot on 3VA4/5/6 breakers — no DIN-rail space consumed, no separate wiring channel. The changeover contact (one NO + one NC) is wired via screw terminals; strip the conductor 15 mm (0.6 in) for proper insertion.
It remains a cataloged accessory for the current 3VA platform.