The 3RT2045-3KB40 is a SIRIUS coupling contactor in the S3 frame size, designed for switching auxiliary circuits or smaller loads where a standard power contactor would be oversized.
Panel fit and wiring — the numbers that matter
The spring-type coil terminals accept the same range without needing a screwdriver — a time-saver on repetitive panel builds.
Switching rates vary by duty class: 900 ops/h in AC-1 (resistive), 400 in AC-2 (slip-ring motors), 1,000 in AC-3 (squirrel-cage motors — the most common), and 300 in AC-4 (plugging/inching). The AC-3e rating also lists 1,000 ops/h — matching the standard AC-3 figure for energy-efficient motor starters. Arcing time is 10 to 20 ms; mechanical response at AC is 16.3 g / 5 ms and 10 g / 10 ms, while DC dropout takes 38 to 57 ms. These timing numbers matter for interlock circuits where the contactor must open before a downstream device re-energises.
Sourcing and lifecycle — active production, no obsolescence worry
Lifecycle stage is listed as current — Siemens continues to manufacture this order code. The 3RT2045-3KB40 is a standard SIRIUS catalog item, stocked broadly across distribution.