What it is
Siemens 6ES7138-4AA00-0AA0 is a pack of five blank reserve modules for the ET 200S distributed I/O system. You mount these in unused slot positions to maintain mechanical integrity, dust protection, and prevent unused connectors from being left exposed.
Panel fit and sourcing
Three dimensions govern fit: 15 mm width matches every ET 200S electronics module slot. Depth 52 mm and height 81 mm are the standard reserve module profile. No wiring, no configuration, no diagnostics — it is a mechanical placeholder only. For the maintenance storeroom, keep a pack on the shelf when building ET 200S cabinets — they disappear into open slots and only get ordered once per line. The 5-piece packaging unit is the only way this code ships.