What this SIRIUS breaker does on a transformer primary
It combines a motor-protective function with a high breaking capacity — 100 kA at both 240 V and 400 V — so it can clear a transformer inrush or secondary fault without upstream fuses blowing. Trip Class 10 keeps the thermal curve fast enough for most dry-type and small oil-filled transformers, but not so fast that normal magnetizing inrush causes nuisance trips.
At 45 mm wide and 97 mm deep, it occupies a standard three-module width on the rail — no special adapter needed. That zero forwards clearance means the breaker can sit flush against a gland plate or back panel without derating. Conductor range: 2x (0.5 to 1.5 mm²) solid or stranded, or 2x (0.75 to 2.5 mm²) — enough for control wiring up to the 10 A rating at 480 V and 600 V.
Breaking capacity and selectivity — where the 100 kA matters
The backup fuse ratings are also specified: gL/gG 50 A at 400 V, 40 A at 500 V, and 40 A at 690 V, giving a coordinated pair for higher fault levels.
Environmental range and storage
That storage range covers unheated warehouses and trucking in winter — the breaker can sit on a shelf for years without degradation, as long as it stays dry.