The Siemens 3RT1026-1AP00-0BA0 is a SIRIUS power contactor in the S0 frame size, with three normally-open main contacts rated for AC-4 switching at 15.5 A at 400 V — the duty cycle for plugging and inching motor loads, not just steady-state running. The 45 mm width and 85 mm height (91 mm depth) fit the standard 35 mm DIN rail per EN 50022, with screw-and-snap-on mounting that locks into place without tools. Main circuit terminals accept solid or stranded conductors: 2x (0.5–1.5 mm²), 2x (0.75–2.5 mm²), up to 2x (0.75–4 mm²) for the control circuit, and 2x (1–2.5 mm²), 2x (2.5–6 mm²), up to 2x 10 mm² for the main circuit — covering most panel wiring from signal-level to motor feed. Auxiliary and control circuits also use screw-type terminals, consistent with the main circuit termination. The contactor carries IP20 on the front face (finger-safe when panel-mounted) and IP00 at the terminals — standard for open-panel installation where the enclosure provides the overall ingress protection.
That difference matters when you're specifying a motor starter package — the 35 A limit gives you a smaller fuse and better selectivity downstream, but the 100 A rating tells you the contactor can survive a fault without welding if the coordination class allows it.