The Siemens SENTRON 3VA1225-5FF42-0BH0 is a 4-pole molded case circuit breaker (MCCB) rated for a continuous current of 125 A, with an insulation voltage of 800 V. It is designed for line protection — the primary role is as a main or feeder breaker in a distribution panel, not a motor-protective device. The 125 A rating is fixed; there is no adjustable thermal or magnetic trip block on this variant, so the breaker is sized for a specific load and cannot be field-reconfigured for a lower ampacity.
Breaking capacity across the voltage range
This MCCB delivers 187 kA interrupting capacity at 240 V AC, dropping to 121 kA at 415 V, 75.6 kA at 440 V, 30 kA at 500 V, and 17 kA at 690 V. These are high-interrupting ratings for a 125 A frame — useful where fault current is high (close to a transformer) and you need selectivity without stepping up to a larger breaker. The 690 V figure (17 kA) is the weakest point: if your system runs at 690 V and available fault current exceeds that, this breaker won't hold. Check the point-of-common-coupling SCCR before specifying.
Thermal derating
Rated 250 A at 40, 45, and 50 °C ambient — that's the continuous current the breaker's thermal-magnetic trip can carry without nuisance tripping. At 55 °C it derates to 243 A, at 60 °C to 237 A, at 65 °C to 230 A, and at 70 °C to 223 A. Operating range is -25 to +70 °C; storage range is -40 to +80 °C. If the panel ambient runs above 50 °C, the derated numbers govern — don't load the breaker to 125 A if the enclosure hits 70 °C.
Built-in auxiliaries and releases
Factory-fitted with an undervoltage release (UVR) and a complement of two auxiliary switches plus one trip alarm switch (HQ). The UVR means the breaker drops out if control voltage is lost — typical for emergency-stop or undervoltage protection schemes. The auxiliary switches provide status feedback (open/closed) and the trip alarm signals a fault condition separately. No communication function on this variant; no ground-fault monitoring.
Physical fit and panel integration
Dimensions: 70 mm deep, 140 mm wide, 158 mm high. This is a standard SENTRON 3VA frame size for a 125 A 4-pole — it mounts on a DIN rail or can be screw-fixed to a backplate. The 140 mm width is the key fit dimension: if your panel was laid out for a narrower 3-pole breaker, this 4-pole won't fit without a wider slot. The trip indicator (mechanical flag) is visible through the front cover, so you can see a trip at a glance without opening the door.