What it is and what it does
The Siemens 3RV2021-1JA20-ZX95 is a SIRIUS motor-protection circuit breaker with Class 10 trip, phase failure detection, and overload and short-circuit protection. Rated short-circuit breaking capacity reaches 100 kA at 400 V AC, so it can safely interrupt a fault up to that level without upstream fuses or a larger breaker cascading in. At 690 V the SCCR drops to 4 kA — still adequate for most 690 V motor circuits, but coordination with upstream protection needs checking at that voltage. Phase failure detection is built in, which is a requirement for any motor-protection device on a three-phase line — a single-phased motor draws locked-rotor current on the remaining phases, and this breaker catches that.
Mounting and panel fit
Mounts via screw or snap-on onto a 35 mm standard DIN rail per EN 60715. The 45 mm width is a single modular unit — that's one 45 mm slot on the rail, leaving the rest of the row for contactors, overloads, or terminals. Depth is 97 mm from the rail face, so check the enclosure depth before committing the gland plate. Mounting position is any orientation, which simplifies layout in tight cabinets. Clearance requirements: 50 mm above and below, 30 mm to the sides, and zero forwards or backwards — so you can pack it against the back panel or a partition without derating. Main circuit terminals are spring-loaded, accepting up to 2× 10 mm² solid or stranded. That covers most motor feeds up to the 10 A rated current at 600 V. No torque driver needed for the spring clamps — just strip 8–10 mm and push in.
How it compares to the 3RV2021-1GA25
The 3RV2021-1GA25 is a sibling in the same SIRIUS frame — same 45 mm width, same DIN-rail mount, same Class 10 trip. The difference is in the current setting range and the SCCR curve. The -1GA25 is rated for a different motor FLA band; the -1JA20-ZX95 covers a specific range that may or may not overlap. If you're swapping one for the other, verify the thermal setting range matches your motor nameplate. The physical footprint is identical, so no panel rework needed.