What it is and what it does
The Siemens 3VA1225-4EF32-0AG0 is a SENTRON molded case circuit breaker (MCCB) with 3 poles, designed for line protection in distribution panels. It carries a TM240 thermal-magnetic release, meaning the thermal element handles overloads and the magnetic element handles short circuits — no electronic trip unit to program, just set it and forget it. Rated 250 A continuous at 40 °C ambient, it holds that rating flat through 50 °C — only starts derating above 55 °C, dropping to 223 A at 70 °C. That thermal headroom matters if the breaker lives in a hot enclosure next to other dissipating gear. Breaking capacity is the headline number here: 121 kA at 240 V AC, 75.6 kA at 415 V, 52.5 kA at 440 V, 17 kA at 500 V, and 11.9 kA at 690 V. At 415 V that's enough to sit upstream of most downstream MCCBs without cascading — the fault current splits across the impedance of the wiring and the downstream breakers, but the upstream device has to survive the full prospective short-circuit current if the fault is bolted at its load terminals.
Physical fit and panel integration
Dimensions: 105 mm wide, 158 mm tall, 70 mm deep. That 70 mm depth is the body only — add the handle throw and any arc-chamber clearance per the manufacturer's mounting instructions. Three-pole footprint matches the standard SENTRON 3VA family, so if you're swapping in a panel that already holds a 3VA frame, the bus-bar and lug positions line up. Rated insulation voltage 800 V, so it's comfortable on 690 V systems with the usual margin. Power loss max 57 W — that's the heat you need to vent if the panel is sealed; a 57 W continuous loss in a small enclosure can push internal ambient above the 70 °C operating limit if there's no airflow. Operating temperature range -25 °C to 70 °C, storage -40 °C to 80 °C. The storage range is wider because there's no current flowing — the breaker isn't self-heating. If the panel sees -25 °C at startup, the TM240 release still operates within its calibrated curve; no warm-up delay.
What the TM240 release means in practice
TM240 is a fixed thermal-magnetic release rated 240 A at the trip threshold. The breaker itself is rated 250 A continuous at 40 °C, so the release is set slightly below the frame's thermal limit — that's normal. The thermal element is non-interchangeable; you can't swap it for a different rating in the field. If the load grows past 240 A, you replace the whole breaker, not just the trip unit. Trip indicator is present — a mechanical flag on the front that shows whether the breaker tripped on overload or short circuit. No undervoltage release, no ground-fault monitoring, no communication function. This is a basic line-protection MCCB: protect the cable, not the process. The auxiliary switch configuration is 1 auxiliary switch + 1 trip alarm switch HP. That gives one set of contacts for status (open/closed) and one dedicated set that only changes state when the breaker trips on fault — useful for remote alarm annunciation without wiring through the main contact position.