What the Ratings Mean for Fit
The 3VA1125-6EF42-0AA0-ZD00: This is a 4-pole IEC frame 160 circuit breaker with a 25 A thermal-magnetic trip unit (TM240, ATAM). The headline number is the 70 kA breaking capacity at 415 V — that's the Icu (ultimate short-circuit breaking capacity), which means it can safely interrupt fault currents up to 70 kA without welding its contacts or failing catastrophically. For a 415 V distribution panel, that puts it in the high-capacity class (class H in Siemens' own grading), suitable for installations with high prospective fault current — think industrial switchboards close to a transformer or a large motor control center. The overload protection is adjustable from 18 A to 25 A (Ir), and the short-circuit pickup (Ii) is set between 6.4 and 12.8 times In — so at the 25 A setting, that's 160 A to 320 A magnetic trip. That range lets you coordinate with downstream branch breakers or motor starters. The N conductor is unprotected on this variant, which is standard for many 3-phase 4-wire systems where the neutral is not expected to carry fault current. The nut keeper kit is included for DC Power OEM builds in China — that's a mounting hardware detail for panel integration.