What this part does on the rail
The Siemens 3RA1902-1B is a plastic side module that clips onto a standard DIN rail adapter to widen it, accommodating larger contactors or circuit breakers in the same footprint. It's designed for the SIRIUS family and fits sizes S00, S0, S2, and S3 — meaning one adapter rail can carry a mixed-size lineup without redrilling the panel.
Dimensions that matter in the enclosure
At 9 mm deep, 10 mm wide, and 97 mm tall, this module adds negligible depth to the adapter rail. The plastic body carries no electrical load; it's purely a mechanical spacer. No derating applies, and no wiring passes through it.
Lifecycle and sourcing status
Because it's a passive mechanical part with a long lifecycle horizon, it's a safe line-item for BOMs that need to stay stable across multiple panel builds.