What this switch does in a 3VA panel
The Siemens SENTRON 3VA9988-0AA22 is a leading auxiliary switch — a changeover contact block that mounts ahead of the main contacts on 3VA1 and 3VA20 through 3VA25 molded-case circuit breakers. It signals the breaker position (ON/OFF/TRIPPED) back to the control system before the main contacts close, which matters for interlocking sequences and status feedback in a motor control center. Rated thermal current (Ith) is 6 A, and the switching capacity varies by duty: AC-12 resistive loads handle the full 6 A at 12–240 V; AC-15 inductive (solenoid/contactor coils) is rated 3 A across the same voltage range. On DC circuits the ratings drop predictably — DC-13 at 24 V is 0.8 A, at 48 V it's 0.4 A. That DC-13 curve is what you check when this switch feeds a PLC input or a DC relay coil in a 24 VDC control loop. Pollution degree 3 and overvoltage category III mean it's rated for the industrial panel environment — conductive dust, humidity cycling, and transient surges up to 4 kV. That's standard for a breaker accessory that lives inside a switchgear enclosure, not a clean-room or office-grade component.
Mounting and wiring fit
The block is 7 mm wide — one modular width on a DIN rail — and 30 mm deep by 56 mm tall. It snaps onto the breaker's left side (leading position) and uses a screw-clamp terminal that accepts 0.2–2.5 mm² conductors with a 15 mm strip length. The 20 ms operating time (make/break) is fast enough for most control sequences but not a high-speed safety relay replacement.