What this MCCB is and what it protects
The Siemens 3VA1125-5EF32-0JA0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection — the primary role of an MCCB in a distribution panel is to detect and interrupt overcurrents and short circuits before they damage downstream wiring or loads. This 3-pole unit carries a TM240 thermal-magnetic overcurrent release, meaning it uses a bimetal element for overload protection and a magnetic coil for instantaneous short-circuit trip. The TM240 designation indicates the thermal pickup is calibrated for a 25 A frame at 40 °C ambient, with the magnetic trip threshold set at 240 A — a fixed, non-adjustable value that suits branch circuits feeding motor starters or resistive loads where the inrush is known. The breaker includes a shunt trip (STL) auxiliary release, which allows remote tripping via a control voltage — useful in emergency-stop circuits or automated shutdown sequences where the MCCB must open without a manual operator present. There is no undervoltage release and no communication function, so this variant is strictly a standalone protective device; it does not report status over a fieldbus.
Breaking capacity — the number that decides selectivity
The interrupting rating is the single most important spec for a sourcing decision on an MCCB because it determines whether the breaker can clear a fault without failing catastrophically, and whether it coordinates with upstream devices. At 240 V, this 3VA1125-5EF32-0JA0 is rated for 187 kA; at 415 V it drops to 121 kA; at 440 V it is 75.6 kA; and at 500 V and 690 V it holds at 17 kA. The steep derating above 440 V is typical for a compact-frame MCCB — the arc-extinction chamber has less volume to stretch and cool the arc at higher voltages. For a 480 V panel in North America, the 75.6 kA at 440 V is the closest published value; for a 690 V wind-turbine or mining application, the 17 kA figure governs. The insulation voltage is rated 800 V, which exceeds the operating voltage in most standard distribution panels and confirms the breaker is suitable for 690 V systems where the insulation must withstand transient overvoltages.
Current rating and thermal derating
Rated 25 A from 40 °C through 50 °C ambient, the TM240 release begins to derate above 50 °C: 24 A at 55 °C and 60 °C, 23 A at 65 °C and 70 °C. The operating temperature range is -25 °C to +70 °C, with storage from -40 °C to +80 °C. If the breaker is mounted in a non-ventilated enclosure near other heat sources, use the 55 °C column as a conservative starting point for continuous load. Maximum power loss is 8.5 W — a modest figure that helps with thermal budgeting inside a crowded panel, but still worth checking against the enclosure's dissipation capacity if multiple breakers are ganged.
Physical fit and mounting
The 3VA1125-5EF32-0JA0 measures 130 mm high, 76.2 mm wide, and 70 mm deep. The width of 76.2 mm (3 inches) is the standard 3-pole MCCB footprint for the SENTRON 3VA1 frame — it occupies three 25.4 mm module positions on a DIN rail or bolts directly to a mounting plate. The depth of 70 mm (2.76 in) is shallow enough to fit in a 200 mm deep enclosure with clearance for rear-connected busbars.