65 A at 480 V AC-3 — S2 Frame Power Switching
The Siemens 3RT2037-3AL20 is a SIRIUS power contactor in the S2 frame size, rated 65 A at 480 V in AC-3 duty — that's the motor-switching rating that governs real-world use for pumps, fans, and compressors up to that current. The coil connection uses spring-type terminals, so no screw tightening on the coil side — just strip and push for solid or ferruled stranded wire up to 2x 2.5 mm².
Switching Performance and Lifecycle
Rated for 10 million mechanical operations typical, with maximum switching rates of 700 cycles/hour in AC-3 and 200 cycles/hour in AC-4 — the AC-4 figure matters for reversing or plugging duty where the contacts make under load. Arcing time spans 10 to 20 ms, and the contactor includes an auxiliary switch block (18...1 configuration) for feedback to the PLC or safety circuit.
DC Load Capability
For DC switching applications, the 3RT2037-3AL20 is rated 10 A at 24 V, 2 A at 48 V, 1 A at 110 V, and 0.3 A at 220 V — these are resistive load figures; inductive DC loads require additional derating or arc suppression. The DC ratings are significantly lower than the AC-3 motor rating because DC arcs do not self-extinguish at zero crossing — the contact gap and arc chute are sized for AC interruption.