What this 40 A MCCB delivers — and what it doesn't
The Siemens SENTRON 3VA2040-6HM32-0AA0 is a 3-pole molded case circuit breaker rated for a continuous current of 40 A across the full ambient temperature range from 40 °C to 70 °C — no derating needed up to that ceiling. That flat thermal curve simplifies panel design: you don't have to oversize the frame for a hot enclosure. It's designed for line protection, meaning it protects cables and busbars against overload and short-circuit, not motor or generator circuits. The 242 kA breaking capacity at 240 V is the headline number, but the real-world figure for a 400 V distribution board is 187 kA at 415 V and 440 V, dropping to 121 kA at 500 V and 3 kA at 690 V. That 3 kA at 690 V is a hard limit — if your system runs at 690 V with higher prospective fault current, this breaker is not the right choice.
Physical fit — panel integration notes
Dimensions are 105 mm wide, 181 mm high, 86 mm deep. Allow additional clearance for the arc chute exhaust and outgoing cable bending radius.
Breaking capacity at a glance — what the numbers mean for coordination
The rated short-circuit breaking capacity (Icu) is 242 kA at 240 V, 187 kA at 415 V and 440 V, 121 kA at 500 V, and 3 kA at 690 V. For a typical 400 V distribution panel, the 187 kA figure gives substantial headroom for high-fault locations like a main switchboard near a large transformer. The 3 kA at 690 V is low — this breaker is not suited for 690 V industrial grids with significant fault current. The insulation voltage rating is 800 V, so the internal clearances and creepage are designed for that voltage class even though the breaking capacity at 690 V is limited.