Siemens 5SY5425-6 — 25 A 4-Pole B-Curve MCB for Universal-Current Circuits
The Siemens 5SY5425-6 is a SENTRON 5SY5-series miniature circuit breaker rated 25 A at 400 V AC and 880 V DC, with a B tripping characteristic that trips between 3 and 5 times rated current — the standard choice for resistive and general-purpose loads where inrush is moderate. Its 4-pole (4P) construction in a 4-module-wide housing (72 mm) covers three-phase-plus-neutral or DC circuits, and the universal-current design (AC/DC rated) means it handles both supply types without derating the frame. Breaking capacity sits at 10 kA per EN 60898 and 15 kA per IEC 60947-2 at DC — the higher figure under the industrial standard matters when the prospective fault current exceeds the domestic-grade limit. The B-curve keeps nuisance tripping low on lighting and control transformer circuits while still clearing a hard short within the let-through energy limits of the downstream wiring.
Mounting and Panel Fit
Snaps onto DIN rail via the quick-assembly system; 70 mm installation depth leaves room behind the breaker for wiring. The 72 mm width (4 width units at 18 mm each) is standard for a 4-pole MCB — no surprises when laying out a multi-row distribution board. Mounting position is any, so vertical or horizontal busbar arrangements work without derating. Combined top and bottom terminals accept incoming feed from either direction — useful when the busbar runs along the top but the panel layout forces a bottom feed. Touch protection is built in, and the sealable cover option (with conductors connected, IP20) satisfies lockout/tagout requirements on panels that need physical isolation verification.
Environmental and Compliance Notes
Rated for ambient temperatures from -40 °C to 75 °C, with humidity derating above 55 °C (95 % RH up to 55 °C, then 55 % RH to 70 °C, 35 % RH to 75 °C). Halogen-free and silicon-free construction suits clean-room or food-processing panels where outgassing contaminates sensitive optics or product. Pollution degree 2 (normal industrial environment, non-condensing).
DC Application Specifics
Rated DC voltage is 880 V (1-pole per string in series), with a maximum DC voltage of 1 000 V and breaking capacity of 15 kA per IEC 60947-2. The DC polarity must be observed when wiring — the supply cord position note says AC as required, but DC requires correct polarity. For a 4-pole breaker used in a bipolar DC circuit, two poles in series per polarity doubles the voltage withstand and arc-quenching margin.