What this breaker does and where it fits
The Siemens 3RV2021-4NA10-ZW96 is a SIRIUS motor protection circuit breaker designed to protect three-phase induction motors against overload and short circuit. It is rated for a supply voltage range of 20 to 690 V and carries a Trip Class 10 characteristic, meaning it will trip within 10 seconds at 7.2× the thermal setting — the standard for standard-duty motor starts where the rotor is not locked for long. The breaker mounts on a 35 mm DIN rail per DIN EN 60715 and can be oriented in any position, which simplifies panel layout when space is tight. Breaking capacity is 25 kA at 400 V, 100 kA at 240 V, and 2 kA at 690 V, so it handles typical industrial fault levels on a 400 V distribution system without needing an upstream fuse for coordination up to that current. At 480 V the continuous current rating is 28 A, and at 600 V it is also 28 A — the same thermal element covers both voltages. Horsepower equivalents are 5 hp at 230 V, 10 hp at 220/230 V, and 20 hp at 460/480 V, which aligns with common NEMA motor frame sizes.
Mounting and wiring clearances
The breaker occupies a 45 mm width on the DIN rail, with a depth of 97 mm and height of 97 mm. Required clearances: 50 mm above and below, 30 mm to the side, and zero forward or backward — so it can be stacked tightly against a backplane or enclosure wall. The screw-type main terminals accept 2×(1…2.5 mm²) or 2×(2.5…10 mm²) solid or stranded copper, with M4 screws for the main contacts. That covers most motor feeder cables up to about 10 mm².
What it detects — and what it doesn't
Phase failure detection is built in, so the breaker will trip if one phase drops out — a common cause of single-phasing motor damage. Ground fault detection is not included; that would require an external ground-fault module or a separate GFCI breaker. The maximum switching rate under AC-3 duty (motor starting) is 15 operations per hour, and the same under AC-3e. Ambient operating temperature range is -20 to +60 °C; storage and transport range is -50 to +80 °C.