What it is and what it does
The Siemens SENTRON 5SP3325-3 is a 3-pole miniature circuit breaker (MCB) with an E tripping characteristic, rated at 25 A and 25 kA breaking capacity at 400 V AC. It is designed as a main miniature circuit breaker for residential buildings and infrastructure applications, per the manufacturer's classification. The E characteristic means it is designed for cable and line protection in installations where inrush currents are moderate — a middle ground between the more common B and C curves, offering a wider magnetic trip threshold that reduces nuisance tripping on transformer or capacitive loads while still protecting against short circuits.
Key ratings and what they mean for fit
The 25 A rating at 400 V AC is the nominal current under standard conditions. At elevated ambient temperatures the breaker derates: 23.75 A at 40 °C, 23.125 A at 45 °C, 22.5 A at 50 °C, and 21.875 A at 55 °C. If your panel runs hot, size the load accordingly — the 25 A nameplate applies only up to 30 °C. The 25 kA breaking capacity at 400 V AC (per EN 60898) means this breaker can safely interrupt a fault current up to 25,000 A without welding its contacts or failing catastrophically. That is a high-interrupting rating for a residential/infrastructure MCB — suitable for installations with high prospective short-circuit current, such as near a transformer substation. Pollution degree 3 and overvoltage category IV mean the breaker is rated for the harsh electrical environment typical of main distribution panels — conductive pollution is possible, and it can handle transient overvoltages at the service entrance. This is not a downstream sub-panel device; it belongs at the origin of the installation.
Panel integration and mounting
Snap-on mounting to 35 mm DIN rail per EN 60715. The breaker occupies 4.5 modular width units (MWUs) — at 18 mm per MWU, that is 81 mm of rail space. Plan your enclosure layout accordingly; this is wider than a standard 1-pole MCB (which takes 1 MWU) because it is a 3-pole unit with a higher interrupting capacity. Dimensions: 128 mm height, 76.3 mm depth (including enclosure depth). The depth is the critical dimension for shallow enclosures — verify your gland plate or backbox depth before committing the BOM line. IP40 with connected conductors; not rated for washdown or outdoor exposure without a secondary enclosure. Terminals accept solid or stranded conductors from 2.5 mm² up to 50 mm² — a wide range that covers both downstream sub-feed wiring and incoming mains cable. Saddle terminals are standard; the infeed can be at the box terminal. The breaker is sealable and lockable via an integrated locking slide, accepting a lock, wire seal, or cable ties — useful for utility metering or tamper-proof installations.
Lifecycle and sourcing posture
For BOM freeze or multi-year project planning, this part carries no imminent obsolescence risk. Sourced and quoted to order through independent distribution; availability and current pricing confirmed at quote time against an RFQ.