What it is — and what the ratings mean for your panel
The Siemens 3VA1140-6EF36-0JA0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection, with a rated current of 40 A at 40 °C and a TM240 thermal-magnetic overcurrent release. The 3-pole construction and 800 V rated insulation voltage suit it for 400 VAC distribution panels where you need both overload and short-circuit protection in one compact footprint. The breaking capacity tells you where this breaker can safely interrupt a fault: 220 kA at 240 VAC, 154 kA at 415 VAC, 121 kA at 440 VAC, and 17 kA at 500 V or 690 VAC. That 220 kA figure at 240 V means it handles high-fault-current scenarios like transformer secondaries or large motor control centers without needing upstream fuses to assist. At 690 V the 17 kA is still respectable for industrial loads at that voltage level. The shunt trip release (STL) allows remote tripping via a control voltage — useful for emergency-stop circuits or interlocking schemes where you need to drop the breaker from a PLC or safety relay. The TM240 release provides thermal-magnetic protection: the thermal element handles sustained overloads, the magnetic element clears short-circuits fast.
Current derating — the real-world rating
This breaker is rated 40 A continuous from 40 °C to 50 °C ambient. Above that it derates: 39 A at 55 °C and 60 °C, 38 A at 65 °C, 37 A at 70 °C. If your enclosure runs hot — say a packed panel near a furnace line — factor that derating into the load calculation. The 10.8 W maximum power loss also contributes to internal heat rise; allow ventilation or spacing in dense DIN-rail layouts. Dimensions are 130 mm height, 76.2 mm width, 70 mm depth — standard 3-pole MCCB footprint that clips onto DIN rail or mounts via the rear panel. The 70 mm depth means it clears most shallow enclosures, but check gland-plate clearance if you're retrofitting into a tight column.