The Siemens 5SP3720-2 is a SENTRON main miniature circuit breaker, single-pole, rated 20 A with an E tripping characteristic. It's built for residential and infrastructure panels — think meter cabinets, distribution boards, anything that needs a compact 1.5 MW-wide (about 27 mm) breaker that seals and feeds a busbar system.
Breaking capacity — the number that matters
Rated 25 kA at 230 V AC per EN 60898, and 25 kA as a rated value. For a residential or light-commercial service entrance, 25 kA gives you headroom over the typical 10–16 kA utility fault level — you don't want the breaker to fail open on a dead short downstream.
E-curve — what that means on site
E characteristic is a deliberate choice: it's a delayed trip curve, sitting between the standard C curve and the selective S curve. It holds through moderate inrush (think transformer magnetizing or motor starting on a small pump) but still clears fast on a hard fault. If you've been swapping out C-curve breakers that nuisance-trip on a cold-start load, this is the fix — it's designed for that middle ground.
Temperature derating — don't ignore it
Rated 20 A at 30 °C ambient, but at 40 °C it's 19 A, at 50 °C it's 18 A, and at 55 °C it's 17.5 A. The insulation voltage is 690 V, so voltage-wise there's headroom.
Mounting and wiring — what fits in the van
Fastens via busbar — clips onto the standard SENTRON busbar system, no DIN rail required (though it can sit on one if the panel is laid out that way). Terminals accept 2.5 mm² to 50 mm² solid or stranded, which covers everything from a 2.5 mm² lighting circuit to a 50 mm² main feed. The infeed is at the box terminal, and the outgoing feeder uses a spring-loaded terminal — no screwdriver needed on the load side, which saves time on a multi-way board.
Environmental and mechanical toughness
Shock-rated at 30 g for 11 ms (three hits), vibration tested per IEC 60068-2-6 at 2 g, 20 cycles from 5 to 150 Hz. IP40 with conductors connected — enough for a closed panel, not for washdown. Pollution degree 3, overvoltage category IV — that's the highest category for distribution boards, meaning it's designed for the incoming supply side, not just downstream branch circuits.
Dimensions for panel layout
Height 151.3 mm, depth 89.5 mm, enclosure depth 76.3 mm. At 1.5 modular width units (roughly 27 mm wide), it's narrower than a standard 2-MW breaker — useful when you're squeezing a main switch and several branch breakers into a compact meter panel. The depth means it clears most shallow enclosures, but check your gland plate clearance if the busbar runs behind it.