SIMATIC S5 IM 300 Interface Module, Centralised Expansion Unit to Central Controller, Without Power Supply

What this part is:
The Siemens 6ES5300-5CA11 is the SIMATIC S5 IM 300 interface module, used in centralised configurations to connect an expansion unit (EU) to a central controller (CC), or to an expansion unit in compact version. It is the EU-side interface without its own power supply, so the expansion rack draws from the configuration rather than a local supply. It is documented for the S5-135U and S5-155U subsystems. German-manufactured new old stock.

What these specs mean in practice:
In practice this is the module that lets an S5 rack grow beyond the slots available in the central controller while keeping the I/O local and centrally configured, as opposed to a distributed setup running over a serial link.

Published ratings and mounting data:

Board size: roughly 200 x 250 x 30 mm (8 x 10 x 1 in)
Weight: about 0.361 kg

Installation and setup notes:
Because S5 interface modules pair specifically between IM300-series senders and receivers, confirm the exact companion module and rack revision before fitting.

Interchange guidance:
SIMATIC S5 is long discontinued, so new old stock and tested-exchange boards are the normal route for keeping S5 plant running.