What the ratings mean for fit
The Siemens 3RV2321-1FC20 is a SIRIUS-brand circuit breaker designed specifically for starter combinations — meaning it integrates with a contactor to form a coordinated motor starter pair, not a standalone feeder breaker. Its 100 kA breaking capacity at 400 V AC tells you it can interrupt fault currents up to that level without upstream fuses needing to clear first, which is the SCCR the panel label carries. At 690 V the breaking capacity drops to 6 kA — a significant derate that governs where this breaker can be placed in a 690 V distribution. The 45 mm width and 97 mm depth fit a standard 35 mm DIN rail per DIN EN 60715, with screw and snap-on mounting. Clearance requirements are 50 mm upwards and downwards, 30 mm at the sides, zero forwards or backwards — that zero forward clearance means the breaker can sit flush against a panel door or backplane without derating. Spring-loaded terminals on the main current circuit accept 2x 1 to 10 mm² solid or stranded conductors — no lug kit needed, but verify ferrule sizing if using stranded wire per local code.
Breaking capacity and motor ratings
The 3RV2321-1FC20 carries a 100 kA breaking capacity at 240 V, 400 V, and 500 V AC — that is the high-fault rating that makes it suitable for industrial panels with large upstream transformers. At 690 V it drops to 6 kA, and at 480 V and 600 V the continuous current rating is 5 A, not the breaking capacity. The motor horsepower ratings span from 0.17 hp at 110/120 V up to 3 hp at 460/480 V and 575/600 V. AC-3 switching duty is rated at 15 operations per hour maximum — that is the thermal limit for motor starting, not a continuous switching rate. For applications requiring frequent cycling, verify this matches the load profile.
Environmental and installation notes
Operating temperature range is -20 to +60 °C; storage and transport range is -50 to +80 °C. The rated voltage span is 20 to 690 V. Mounting position is any. No ground fault detection and no phase failure detection are built in — those functions, if required, must come from an external relay or the upstream motor protection scheme.