What it is and what it does
The Siemens SENTRON 3VA1125-5EF36-0DA0 is a 3-pole molded case circuit breaker (MCCB) designed for line protection — the primary overcurrent and short-circuit protection device in a distribution panel. It carries a continuous current rating of 25 A at 40 °C, derating slightly to 23 A at 70 °C, so on a warm panel you still have headroom for a 20 A load without nuisance tripping. The TM240 thermal-magnetic release handles overloads and short-circuits; the integrated undervoltage release (UVR) drops the breaker if control voltage falls, which is useful for emergency-stop circuits or mains-failure protection.
Breaking capacity — what the numbers mean for your panel
The interrupting rating is 187 kA at 240 V, 121 kA at 415 V, 75.6 kA at 440 V, and 17 kA at 500 V and 690 V. At 240 V that 187 kA figure is high — it will clear a fault on a large transformer secondary without the arc re-striking. At 690 V the 17 kA still covers most industrial motor circuits. The insulation voltage is rated 800 V, so the breaker itself can live on a 690 V bus with proper coordination.