What it is — and what the ratings mean for fit
The Siemens 3VA4145-4ED24-3AA0 is a 2-pole circuit breaker from the 3VA4 family, UL Frame 125, with a TM210 thermal-magnetic trip unit. The 'S' breaking capacity class means it can interrupt 25 kA at 480 V — that's the fault it can clear without welding its contacts or blowing apart. That rating governs whether it holds on a high-capacity transformer secondary or a stiff industrial feed; if your available fault current exceeds 25 kA at that voltage, you step up to the next class. In=45 A, Ir=45 A fixed — no adjustment band, no dial. The overload protection is locked to 45 A. Short-circuit pickup Ii is fixed at 10 x In, so 450 A instantaneous. That's a standard motor-circuit or feeder-protection profile: lets inrush pass, trips fast on a bolted fault. If you need adjustable Ir or a lower Ii for a long cable run, this isn't the variant. Mounts on a DIN rail inside a panel. The 2-pole format fits single-phase or two-leg protection of a 208/240 V split-phase load, or a 480 V line-to-line load where a 3-pole breaker would waste a pole. The packaging box dimensions (472 x 396 x 213 mm) give you the shipping cube; the breaker itself fits the standard 18 mm per pole DIN-rail footprint.
Lifecycle and sourcing reality
Export control is AL: N / ECCN: EAR99 — no special license needed for most destinations. RoHS compliance dates from 2019-05-13. REACH Article 33 duty applies: lead (CAS 7439-92-1) above 0.1% w/w in the candidate list. That's a disclosure requirement, not a restriction — your quality or compliance team may want the declaration on file for the BOM audit trail.