What it is and what it does
The Siemens 3VA1125-4EF32-0BA0 is a 3-pole molded case circuit breaker (MCCB) from the SENTRON family, designed for line protection — meaning it sits upstream in a distribution panel protecting cables and busbars from overloads and short circuits. Rated continuous current Iu is 25 A, with a TM240 thermal-magnetic trip unit that provides fixed thermal and magnetic settings. The interrupting ratings are voltage-dependent: 121 kA at 240 V, 75.6 kA at 415 V, 52.5 kA at 440 V, and 11.9 kA at 690 V — so the available fault current at the panel's supply voltage determines which rating applies. Rated insulation voltage Ui is 800 V, giving headroom for 690 V systems.
Thermal derating and panel integration
The breaker carries 25 A continuously up to 50 °C ambient; above that it derates linearly to 22.5 A at 70 °C. In a sealed panel or high-ambient cabinet, that derating curve governs the actual load you can protect — not the 25 A nameplate. Dimensions are 130 mm height, 76.2 mm width, 70 mm depth, fitting standard 3-pole MCCB panel cutouts. Front protection is IP40, so the operator face is touch-safe; the rear and sides rely on the panel enclosure for IP rating.
Undervoltage release and auxiliary options
This variant includes an undervoltage release (UVR) — designated as 3VA9608-0BB11 — so the breaker trips automatically when supply voltage drops below a threshold. No auxiliary contact version is fitted (no status feedback contact), and there is no communication function, phase failure detection, ground fault monitoring, or voltage trigger. The trip indicator is also absent. For applications requiring remote status or shunt trip, the UVR is the only integrated release; additional functions require add-on modules.