What It Is and Where It Fits
The Siemens SENTRON 3VA9988-0AA23 is a leading auxiliary switch — a changeover switch with changeover contacts type HQ (7 mm) designed as an electronic accessory for 3VA1 and 3VA20 up to 3VA25 circuit breakers. It snaps onto the breaker's left side (leading position) to signal the main contact position to a PLC or indicator lamp. Rated thermal current is 0.3 A, with switching capacities defined per duty class: 0.3 A at AC-12 and AC-15 (12 V or 24 V), 0.1 A at DC-12 (12 V or 24 V), and 0.07 A at DC-13 (12 V or 24 V). The DC-13 rating is the one that matters for solenoid or contactor coil feedback — it's derated because of the inductive load's arc energy. Overvoltage category III and a surge voltage resistance of 4 kV mean this switch is rated for fixed-installation panels downstream of the main distribution board — not just for final circuits. Pollution degree 3 (conductive pollution or dry non-conductive that becomes conductive) is typical for industrial control cabinets where the switch lives near the breaker's arc chamber.
Integration Notes
The 7 mm width matches the modular width of a single 1-pole SENTRON 3VA breaker pole. It clips directly onto the breaker's left side; no additional DIN-rail space is consumed beyond the breaker's own footprint. Depth is 30 mm, height 56 mm — it stays within the breaker envelope, so panel layout and gland-plate clearance are unaffected. Strip length for the connecting wire is 15 mm (0.6 in). The 20 ms lead time (relating to main contacts) means the auxiliary contact follows the main contact within 20 ms — fast enough for most PLC scan cycles but not for safety-rated mirror contacts (those require < 5 ms). Minimum operating voltage is 24 V DC — below that the switch may not reliably change state. The thermal current of 0.3 A is the continuous carry limit; switching inductive loads (DC-13) should be kept to 0.07 A at 24 V to avoid contact erosion.