What it is and what it does
The Siemens 3RU7136-1JB0 is a SIRIUS S2 thermal overload relay — the part that sits between the contactor and the motor to protect against sustained overcurrent. It's a thermal bimetallic design, Trip Class 10, meaning it will trip within 10 seconds at 7.2x the current setting. That's the standard speed for protecting standard squirrel-cage induction motors during start-up. Rated operational current is 10 A, which sets the maximum motor full-load current you can protect. The relay mounts directly onto a S2-size contactor — no separate DIN-rail footprint needed. That saves a slot in the panel, but it also means the relay and contactor come out together if you're swapping a failed unit.
Mounting and integration
Fastening method is contactor mounting — it snaps onto the S2 contactor, not onto a DIN rail. The mounting position is flexible: vertical surface, rotatable ±135° or tiltable ±45° front-to-back. That helps when the panel layout is tight or the gland plate forces an odd angle. Dimensions are 118 mm deep, 55 mm wide, 105 mm tall. The 55 mm width is the critical number for side-by-side spacing in a panel — you need 6 mm clearance to grounded parts on the side. Terminals are screw-type on both main and auxiliary circuits; torque the mains at 3–4.5 N·m, auxiliaries at 0.8–1.2 N·m.