What it is and what it does
The Siemens 3RV2021-4FA15-ZX95 is a SIRIUS-branded motor protection circuit breaker, designed specifically for motor protection with phase failure detection and a Class 10 trip characteristic. It mounts on 35 mm DIN rail per DIN EN 60715, using either screw or snap-on fastening, and accepts any mounting position. The Class 10 trip class means it disconnects within 10 seconds at 7.2× the thermal setting — fast enough to protect standard induction motors during a locked-rotor event, without nuisance tripping on normal starting inrush. Phase failure detection is built in, so a lost phase on the line side won't leave the motor running single-phased. Breaking capacity is 100 kA at 240 V and 10 kA at 400 V, which covers most industrial panel fault levels. At 230 V it's rated for 7.5 hp motor load; at 480 V and 600 V the continuous current rating is 40 A.
Panel integration and wiring
At 45 mm wide, 97 mm deep, and 97 mm tall, this breaker occupies a single 45 mm DIN slot — standard for motor-protection breakers in this class. The 70 mm clearance required above and below (and 30 mm to the side) is for arc venting and thermal dissipation; pack it tighter and you lose the interrupting rating. Main circuit terminals are M4 screw-type, accepting 2×(0.5…1.5 mm²) or 2×(0.75…2.5 mm²) solid or stranded copper. Strip length isn't given in the spec, but standard practice for M4 screw terminals on this class is 8–10 mm. The auxiliary contact block (if used) shares the same terminal size.