DC-rated miniature circuit breaker for 440 VDC rail
The Siemens 5SY5225-7CC12 is a 2-pole miniature circuit breaker from the 5SY5 series, rated C25 curve with a 440V DC breaking capacity of 10kA. This is a DC-rated MCB designed for direct-current applications like DC bus distribution, battery banks, or solar combiner boxes — not a general-purpose AC breaker pressed into DC service. The C25 trip characteristic means it holds 25 A continuous and trips magnetically between 5x and 10x rated current (125–250 A), sized for motor or transformer inrush without nuisance trips on a 440 VDC rail.
What the DC rating means for fit
The 440V DC rating at 10kA is the key selection parameter here. Unlike an AC breaker, a DC MCB must extinguish an arc that has no natural current zero crossing. The 5SY5 series uses a permanent-magnet blowout design to stretch and quench the DC arc. On a 440 VDC bus, this breaker safely interrupts fault currents up to 10 kA without welding contacts or cascading upstream. The 2-pole construction switches both the positive and negative lines, which is standard for ungrounded DC systems. For a 24 VDC control circuit this is overkill; it belongs on the main DC power distribution.