Size S2 Class 10 — what the ratings mean out here
The 3RU2136-4JB1: This is a SIRIUS thermal overload relay, Size S2, designed to protect a motor from sustained overcurrent by tracking the heat buildup in the windings — the bimetallic strip bends and trips the contactor when the current stays high too long. Class 10 trip means if the motor draws 7.2 times the full-load current, the relay opens in under 10 seconds — fast enough to keep the rotor from cooking on a stalled pump or jammed conveyor. Rated insulation voltage is 690 V, and the motor power ratings at that voltage hit 55 kW — so it handles a 75-hp-class motor at 690 V three-phase without the insulation breaking down.
Panel fit and thermal budget
The relay measures 55 mm wide by 105 mm tall by 117 mm deep — it mounts in any orientation, stand-alone on the panel or ganged with a contactor, and the screw terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded wire. Each pole dissipates 5.2 W at full load — in a sealed enclosure with a few of these, the heat adds up. The operating range is -40 to +70 °C, with temperature compensation active from -40 to +60 °C so the trip curve stays accurate even if the panel gets warm.
Auxiliary contact ratings for the control circuit
The integrated auxiliary switch handles 2 A at 24 V DC, 3 A at 120 V AC, and 2 A at 230 V AC — enough to drive a PLC input or a signal lamp. At 400 V AC it's rated 1 A, and at 690 V AC it drops to 0.75 A, which covers the higher-voltage control schemes in some European panels. The trip indicator shows a "Tripped" message on the front — no guessing whether the relay opened on overload or someone bumped the reset.