What it is and what it does
The Siemens 3VA1112-5MH36-0BH0 is a 3-pole IEC molded-case circuit breaker from the 3VA1 frame 160 series, rated 125 A continuous current. Its headline spec is the 55 kA breaking capacity at 415 V (class M), which means it can safely interrupt a fault current up to that level without upstream devices needing to clear it first — a key figure for panel builders coordinating selectivity in a distribution board or motor control center.
Key ratings and what they mean for fit
The breaker is configured for starter protection with a TM120M thermal-magnetic trip unit set at 125 A. The 'without overload protection' note means the thermal element is bypassed — this unit provides only short-circuit protection, with adjustable instantaneous pickup (Ii) from 5 to 15 times In. That makes it a fit for motor branch circuits where overload protection is handled separately by an overload relay or soft starter. The undervoltage release (UVR) is 24 V DC. When control voltage drops below the dropout threshold, the UVR trips the breaker open — standard practice for emergency-stop circuits or undervoltage protection on machine tools. Two auxiliary switches (HQ) and one trip alarm switch (HQ) are integrated, giving the PLC or safety relay status feedback on the breaker position and fault condition.
Deployment context
This breaker mounts on a DIN rail or can be screw-fixed to a backplate in a standard IP2X enclosure. The clamp connection terminals accept copper or aluminum conductors up to the rated cross-section for the 125 A frame. In a motor control center, it typically sits in the feeder section ahead of the contactor and overload relay, providing the short-circuit protection that the overload relay alone cannot handle.