What the 55 kA @ 415 V rating means for your panel
The Siemens 3VM1125-5EE46-0AA2 is a 4-pole IEC frame 160 circuit breaker with a breaking capacity class M rating of 55 kA at 415 V AC. That 55 kA figure is the maximum fault current the breaker can safely interrupt at that voltage without welding contacts or rupturing the arc chamber — critical for main or feeder breakers in high-fault-capacity installations like transformer secondaries or large motor control centers. The thermal-magnetic trip unit is a TM220 (ATFM type), with the continuous current rating In set at 25 A and the overload protection band Ir adjustable from 18 A to 25 A, giving the panel builder a ±28 % range to match the downstream load without swapping the breaker body.
Short-circuit protection and selectivity
The instantaneous short-circuit pickup Ii is fixed at 12.8 × In — that is 320 A for the 25 A rating. This fixed multiple means the breaker coordinates predictably with downstream branch devices: a 320 A magnetic threshold clears bolted faults fast while riding through motor inrush and transformer energization. The N conductor is unprotected (solid neutral), so this breaker is intended for 3-phase + N systems where the neutral is not switched or protected — typical for TN-S or TN-C-S distribution. Terminal connection type is standard screw-clamp, sized for the 160 A frame lugs.