MCCB for line protection — 125 A, 4-pole, TM240 release
The Siemens SENTRON 3VA1225-5FF42-0AG0 is a 4-pole molded case circuit breaker rated 125 A continuous, designed for line protection in distribution panels. Its TM240 thermal-magnetic release provides fixed overload and short-circuit protection without adjustable trip settings — a straightforward choice for feeder circuits where coordination studies have already locked in the pickup. The interrupting capacity reaches 187 kA at 240 V AC, 121 kA at 415 V, and 75.6 kA at 440 V, so it handles high-fault scenarios common in industrial mains without cascading upstream.
Thermal derating and panel integration
At 40 °C the breaker carries the full 125 A; derating begins above 55 °C, dropping to 243 A at 55 °C and 223 A at 70 °C. The 70 mm depth and 140 mm width fit standard MCCB panel footprints — verify gland-plate clearance against the existing cutout before committing the BOM. Maximum power loss of 57 W means the enclosure must dissipate that heat; adjacent devices in a sealed cabinet may need spacing or forced ventilation.
Key ratings at a glance
Rated insulation voltage is 800 V, covering 480/600 V class systems with margin. Operating temperature range is -25 °C to 70 °C; storage range extends from -40 °C to 80 °C. The supplied basic switch carries order code 3VA12255FF420AA0 — relevant when ordering spare internal mechanisms.