What this MCCB delivers — and what the ratings mean for your panel
The Siemens SENTRON 3VA1112-5EF36-0DA0 is a 3-pole molded case circuit breaker (MCCB) rated 125 A at 40 °C, with a TM240 thermal-magnetic overcurrent release. The headline breaking capacity is 187 kA at 240 V AC — that is the maximum fault current it can safely interrupt without welding contacts or rupturing the case. At 415 V the rating drops to 121 kA, at 440 V to 75.6 kA, and at 500 V and 690 V to 17 kA; this is typical for an MCCB where arc extinction gets harder as voltage rises. The part carries an undervoltage release (UVR) as the auxiliary release — if control voltage drops below the dropout threshold, the breaker trips, which is useful for undervoltage protection on motor circuits or as a remote shunt trip via a contactor coil.
Thermal derating and panel integration
The breaker holds its full 125 A rating from 40 °C up to 50 °C, then derates to 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, and 114 A at 70 °C. If the panel ambient runs hot — say a crowded enclosure with drives — size the load at the 70 °C figure, not the nameplate 125 A. Dimensions are 130 mm high, 76.2 mm wide, 70 mm deep; the 76.2 mm width is three standard 25.4 mm pole pitches, so it fits a standard DIN-rail or panel-mount footprint without extra adapters. Power loss is 30.6 W maximum — account for that in the enclosure thermal calculation.