What the ratings mean for fit
The 3RK1903-0AL10: Because this is a terminal module and not a contactor or power block, its key spec is the 130 mm width — that's the space it occupies on the DIN rail inside the ET200S assembly. If your panel layout was designed around a standard 55 mm contactor footprint (like the SIRIUS S2 frame), this module is over twice the width, so it won't drop into the same slot without re-railing. The 'without supply line connection' variant means it takes its feed from an adjacent module — verify the busbar or jumper scheme in your existing ET200S string before committing the BOM line.
Deployment context
This module snaps onto a 35 mm DIN rail per DIN EN 50022 — standard for Siemens ET200S distributed I/O and motor starter systems. It's rated IP20 on the front, so it belongs inside a control cabinet, not in a washdown or outdoor zone. If you're retrofitting into an existing ET200S station, check the slot assignment: the High Feature Reversing starter requires this specific terminal module to handle the reversing contactor wiring; a standard ET200S terminal module won't carry the same internal bus routing.