What this MCCB is and what it does
The Siemens SENTRON 3VA1112-4EF36-0BC0 is a 3-pole molded case circuit breaker (MCCB) rated 125 A at 40 °C, designed for line protection in distribution panels. Its 121 kA breaking capacity at 240 V AC means it can safely interrupt fault currents up to that level without upstream damage — critical for high-fault installations like transformer secondaries or large motor control centers. Rated insulation voltage is 800 V, so it handles 480/600 V class systems with headroom. The breaker carries an undervoltage release (UVR) and two auxiliary switches (HQ type) factory-fitted — the UVR trips the breaker if control voltage drops, standard for emergency-stop or undervoltage protection schemes.
Breaking capacity across voltages — where it fits
Breaking capacity drops as voltage rises: 121 kA at 240 V, 75.6 kA at 415 V, 52.5 kA at 440 V, and 11.9 kA at both 500 V and 690 V. At 415 V it still clears 75.6 kA — enough for most industrial low-voltage switchgear. At 690 V the 11.9 kA figure limits it to lower-fault applications unless coordinated upstream.
Thermal derating — the real current rating
Full 125 A holds from 40 °C through 50 °C. At 55 °C it derates to 122 A, at 60 °C to 120 A, at 65 °C to 117 A, and at 70 °C to 114 A. If the panel ambient runs hot — say next to a drive cabinet — size the load at the derated figure, not the 125 A nameplate.
Physical fit and panel integration
Dimensions: 130 mm high, 76.2 mm wide, 70 mm deep. That 70 mm depth is shallow enough for most 200 mm deep enclosures without crowding the gland plate. Three-pole footprint matches standard SENTRON 3VA MCCB cutouts — drops into existing DIN-rail or screw-mount backplates without panel rework.
Operating environment and power loss
Operates from -25 °C to 70 °C ambient; storage range -40 °C to 80 °C. Maximum power loss is 30.6 W — factor that into enclosure thermal calculations, especially in sealed cabinets.