The Siemens 3VA9988-0AA21 is a SENTRON leading auxiliary switch designed as an accessory for the 3VA family of molded-case circuit breakers. It signals the breaker's open/closed position to a control system or indicator circuit — a standard requirement for remote monitoring and interlocking in distribution panels. Rated thermal current (Ith) is 10 A, which defines the continuous current-carrying capacity through the switch contacts. For AC control circuits, the AC-15 rating (6 A at 24 V, 6 A at 125 V, 2 A at 400 V) covers solenoid and contactor coil loads — the typical application for an auxiliary switch in a motor control center. For DC circuits, the DC-13 rating (3 A at 24 V, 0.2 A at 110 V) covers switching inductive loads like DC contactors and relays. Pollution degree 3 and overvoltage category III mean the switch is rated for the industrial environment inside a panel — conductive pollution is expected, and it can handle transient overvoltages from the mains distribution side. That is the standard rating for a breaker accessory mounted in a main distribution board or motor control center.
Panel fit and wiring
Physical footprint is 14 mm wide, 56 mm high, 30 mm deep — a single-module width that clips directly onto the 3VA breaker's side. Stripped length of 15 mm (0.6 in) matches standard ferrule or bootlace-ferrule preparation for the screw-clamp terminals. No DIN-rail space consumed; the switch mounts on the breaker itself.