What the CLASS 20E rating means for motor protection
The Siemens 3RB2025-2QB0 is a SIRIUS solid-state overload relay with a CLASS 20E trip class, meaning it allows a motor to run at up to 720% of its full-load current for 20 seconds before tripping — the standard protection curve for standard induction motors driving pumps, fans, and conveyors where starting inrush is moderate and a faster trip (Class 10) would nuisance-trip on start. Rated for AC-3 duty up to 690 V, it covers 400 V and 480 V motor circuits common in North American and European panels, with pollution degree 3 rated voltage matching the same 690 V figure — so it's suited for industrial environments with conductive dust or humidity.
Mounting and integration into a contactor assembly
This relay mounts directly onto a contactor — no separate DIN-rail footprint needed — saving panel width. Main circuit connections use screw-type terminals accepting 0.5 to 4 mm² solid or 2x 0.5 to 2.5 mm² stranded, with AWG equivalents 14 to 10 for the main contacts. Auxiliary contact ratings are voltage-dependent: 2 A at 24 V, 4 A at 120 V, 3 A at 230 V — so verify the control voltage when sizing the aux circuit.
Environmental and compliance profile
The 3RB2025-2QB0 carries ATEX certification PTB 06 ATEX 3001 Ex II (2) GD, permitting installation in Zone 2 gas and Zone 22 dust atmospheres — a critical spare for food-and-bev or chemical lines where an explosive environment is a real possibility. Front protection is IP20 — finger-safe but not washdown-rated. EMC immunity includes 2 kV burst on power ports and 1 kV on signal ports (severity level 3 per IEC 61000-4-4), plus 6 kV surge voltage resistance. These figures mean it's unlikely to false-trip from nearby contactor switching or line transients in a typical panel.