What This Contactor Delivers on the Line
The Siemens 3RT1045-3BB44-3MA0 is a SIRIUS size S3 power contactor rated for 37 kW at 400 V in AC-2 duty — the standard for slip-ring motor starting and reversing. That AC-2 rating is the one that governs real-world motor switching; the 66 A AC-4 rating (at 400 V) covers inching and plugging cycles where the contactor makes and breaks stalled-rotor current. If your line uses jogging or reversing on conveyors or hoists, the AC-4 figure is the one that decides contact life. Coil is 24 V DC, pulling 0.8 A on pickup. That's a standard PLC-level control voltage — no separate power supply needed if your cabinet already runs 24 VDC. The contactor mounts via screw or snap-on onto 35 mm or 75 mm standard DIN rail, so it fits the same profile as the rest of the SIRIUS family.
Panel Fit and Clearance
Footprint is 70 mm wide by 146 mm tall by 201 mm deep. That depth is the one that catches panel builders — it's deeper than a typical S2 contactor, so verify gland-plate clearance and door swing before laying out the backplane. Side-by-side mounting is allowed, which helps when you're stacking multiple contactors on a motor control center bus. Terminals are screw-type on the main circuit, accepting 2x (10–50 mm²) stranded or 2x (0.25–2.5 mm²) solid. The auxiliary circuit handles 2x (2.5–16 mm²) solid/stranded. Pollution degree 3 means it's rated for conductive dust and humidity typical of industrial floors — no derating needed for dirty environments. IP20 on the front with the cover on; the terminal area is IP00, so it needs enclosure protection against accidental contact. Operating temperature range is -25 to +60 °C, storage down to -55 °C. If your panel sits near a furnace line or in an unheated warehouse, the -25 °C floor is fine for most plants; the +60 °C ceiling handles interior cabinet heat rise without forced ventilation.
Switching Cycles and Contact Life
Mechanical life is a typical 10 million operations — that's the contactor frame, not the contacts. Electrical life depends on duty: at AC-3 (standard squirrel-cage motor start/run) you get up to 1,000 cycles per hour; at AC-4 (inching/jogging) it drops to 300 cycles per hour. The arcing time is 10–15 ms (14–20 ms on DC), which is deterministic enough for most sequencing logic, though a safety PLC may want to verify the auxiliary contact state before releasing the next motion command.
Sourcing and Lifecycle
This is a quoted-to-order item through distribution. The SIRIUS series is widely stocked, but the -3MA0 variant may not sit on every distributor's shelf. Send an RFQ with your quantity and target delivery window.