What this MCCB carries — and where the rating matters
The Siemens SENTRON 3VA1112-5EF32-0BH0 is a 3-pole molded case circuit breaker rated for line protection at a continuous 125 A (Iu). The interrupting capacity climbs to 187 kA at 240 V, drops to 121 kA at 415 V, 75.6 kA at 440 V, and 17 kA at 690 V — so at the common 400 V class the breaker clears 121 kA without cascading upstream. The TM240 thermal-magnetic release handles the overload curve; an undervoltage release (UVR) is built in, and the auxiliary contact block gives two spare changeovers plus a dedicated trip alarm switch (2 aux + 1 alarm HQ).
Derating and thermal profile — the real continuous current
The 125 A rating holds flat from 40 °C through 50 °C ambient. At 55 °C it derates to 120 A, at 60 °C to 117.5 A, at 65 °C to 115 A, and at 70 °C to 112.5 A — a 10 % drop from nameplate at the top of the operating range. If the panel ambient runs above 50 °C, size the branch circuit for the derated figure, not the 125 A label.
Mechanical footprint and panel fit
The breaker measures 130 mm high, 76.2 mm wide, and 70 mm deep — a standard 3-pole MCCB footprint for a 125 A frame. Front protection is IP40, so it tolerates dust ingress on the panel face but not washdown. Storage range spans -40 °C to 80 °C; the operating floor is -25 °C, fine for unheated enclosures in temperate climates.