32-channel DC input module for S7-300 racks
The Siemens 6ES7321-1BL00-4AA1 is a SM 321 digital input module with 32 channels, each accepting 24 VDC and drawing 7 mA at signal '1'. It snaps onto the S7-300 DIN rail and connects to the backplane bus via the standard 40-pin front connector. The module footprint is 40 mm wide by 125 mm high by 120 mm deep — it occupies one slot in the rack and leaves room for adjacent modules in a dense panel layout.
Lifecycle status and sourcing reality
Typical lead time is quoted at 1–10 working days from the point of order confirmation, though this depends on lot size and current channel stock.
Electrical and thermal profile
Each input sinks 7 mA at the '1' signal level — this is the load the field sensor or switch must drive. The total backplane current draw for all 32 channels at 24 VDC is well within the S7-300 rack power budget. Typical power loss is 6.5 W. This heat dissipates into the enclosure; for cabinets with multiple modules, the cumulative thermal load should be factored into the ventilation or cooling design.