Lateral auxiliary switch for 3RT2 contactors
The 3RH2911-1DA20 is a lateral-mounted auxiliary switch block from the Siemens SIRIUS family, designed to snap onto the left or right side of a 3RT2 contactor. It adds two normally-open (NO) auxiliary contacts — terminals 43/44 and 53/54 on the left side, or 23/24 and 33/34 on the right — giving the contactor feedback or interlocking capability without extra wiring space.
Current ratings across duty and voltage
The contact rating is 10 A maximum, but the usable current depends on the switching voltage and duty. At 24 V it handles 6 A in one duty class and 10 A in another — the difference reflects AC vs DC or resistive vs inductive load capability. For AC-15 pilot duty at 690 V it is rated 1 A, which covers most PLC input and relay coil switching in 480 V panels. At higher DC voltages the current drops sharply: 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V. This matters when the auxiliary switch is used to break DC control circuits — the arc extinguishes differently than AC, so the derating is real and must be factored into the BOM.
Mechanical life and contact reliability
Rated for 10 million mechanical switching cycles typical, with a contact reliability of one faulty switching per 100 million operations at 17 V, 1 mA. That means the contacts are reliable down to low-level signals — useful for direct PLC input sensing without a separate interface relay.
Insulation coordination and environmental limits
Rated insulation voltage is 690 V AC at pollution degree 3, with a surge voltage resistance of 6 kV. This puts it in the same insulation class as the contactor it mounts to — no derating needed for standard 480 V motor control panels. Operating temperature range is -25 to +60 °C, storage from -55 to +80 °C.
Mounting and connection details
Snap-on mounting to the contactor — no DIN rail required for the auxiliary block itself. Dimensions are 10 mm wide, 57.4 mm high, 66 mm deep. Screw-type terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) with core end processing, or 2x (20 to 16 AWG) and 2x (18 to 14 AWG) for stranded wire. IP20 protection on the front face.