What It Is and Where It Fits
The Siemens 3RB2026-1ND0 is a SIRIUS solid-state overload relay for three-phase motor protection. It monitors the main current circuit (3 poles) and trips on overload per CLASS 10E, meaning it will disconnect before the motor windings exceed their thermal limit under a locked-rotor condition. This is the relay you specify when the motor starter needs to survive a high-inertia start without nuisance tripping, yet still protect against sustained overload. Mounts directly onto a contactor via the contactor mounting fastening method — no separate DIN-rail footprint needed, saving panel width. The 45 mm width matches the SIRIUS contactor family, so it integrates into a coordinated starter assembly without extra bracketing.
Hazardous-Area and Compliance Profile
Carries ATEX approval PTB 06 ATEX 3001 Ex II (2) GD, certifying it for installation in or associated with Zone 1 / Zone 2 gas and Zone 21 / Zone 22 dust atmospheres per IEC 60079. The (2) designation means it is a associated apparatus — it can be installed in the safe area and protect the motor in the hazardous zone. Confirm the Ex marking before specifying; this is not a Zone 0 device. Surge voltage resistance rated at 6 kV, and immunity to electrical fast transients (burst) per IEC 61000-4-4 at severity level 3: 2 kV on power ports, 1 kV on signal ports. This is sufficient for industrial panels without dedicated surge suppression on the control transformer. RoHS substance prohibition date is 07/01/2006, so the part is compliant with the original RoHS directive.
Terminals and Wiring — What Fits
Main current circuit uses screw-type terminals accepting 2x (0.25... 1.5 mm²) solid or 2x (14... 10) AWG. Auxiliary and control circuit uses spring-loaded terminals accepting 2x (0.25... 1.5 mm²) finely stranded with core end processing or 2x (24... 16) AWG. The spring-loaded aux terminals save wiring time on the control side — no screw tightening, just insert and lock. Auxiliary contact ratings are voltage-dependent: 2 A at 24 V, 4 A at 120 V, 3 A at 230 V. For DC switching: 0.55 A at 60 V, 0.3 A at 110 V and 125 V, 0.11 A at 220 V. These are the make/break capacities for the control circuit — do not exceed them when driving PLC inputs or contactor coils. Power dissipation per pole is 0.02 W, negligible for panel thermal budgeting. Mounting position is any, so it works in horizontal or vertical bus runs. Clearances: 0 mm upwards, forwards, backwards, and downwards; 6 mm at the side.
Environmental and Mechanical Ratings
Operates at -25 to +60 °C ambient, stores and transports at -40 to +80 °C. Relative humidity during operation up to 100 % — no derating for condensation, but verify the enclosure rating if used in condensing environments. Shock resistance is 15g / 11 ms, sufficient for panel-mounted applications on vibrating machinery. Dimensions: 73 mm height, 45 mm width, 75 mm depth. The 75 mm depth is the projection from the contactor face — check clearance against the enclosure door or busbar shroud.