What this breaker is and what the ratings mean
The Siemens 3VA1112-6MH36-0KH0 is a 3-pole molded case circuit breaker on the IEC frame 160 platform, rated In=125A with a TM120M thermal-magnetic trip unit. The 'H' breaking capacity class delivers Icu=70kA at 415 V AC — that means it can safely interrupt a fault current up to 70,000 amps without self-destructing, which is the figure you need for high-fault panel coordination studies. This is not the standard 'N' or 'S' class; H-class is specified when the available fault current at the panel exceeds 50 kA. The trip is configured for starter protection (TM120M, AM) with short-circuit pickup Ii adjustable from 5 to 15 times In (625 A to 1875 A). Note the description explicitly states 'without overload protection' — the TM120M provides the thermal element, but the listing flags no overload protection, so verify whether your motor starter or soft starter handles the overload function separately. The shunt trip (STL) operates on 220-250 V DC or 208-277 V AC, letting you remotely trip the breaker from a safety relay or E-stop circuit.
Auxiliary and alarm switching
Two auxiliary switches (HQ) plus one trip alarm switch (HQ) are built in. The aux switches signal the breaker's open/closed position to a PLC or status lamp; the alarm switch changes state only when the breaker trips on a fault, not on a manual open. That distinction matters for remote fault diagnostics — the alarm contact tells you the breaker didn't just get turned off, it cleared a fault.
Termination and panel fit
Clamp-type terminals accept copper or aluminum conductors without lug kits for most panel applications. The IEC frame 160 footprint is standard for Siemens 3VA1 series — mounts on a DIN rail or panel-mount adapter. Verify the shunt trip voltage matches your control voltage before wiring; the STL coil draws continuous power when energized, so factor that into your 24 V DC supply budget if stepping down from the listed 220-250 V DC range.