The Siemens 5SP3820-3 is a SENTRON main miniature circuit breaker, 3-pole (3P), rated 20 A at 400 V AC with an E tripping characteristic. The E-curve is a Siemens-specific characteristic that sits between the standard B and C curves — it trips between 2.5 and 4 times rated current, making it a good fit for transformer inrush or motor-start loads where a B curve would nuisance-trip but a C curve might be too slow for short-circuit protection.
Thermal derating and wire sizing
The 20 A rating holds at 30 °C ambient; at 40 °C it derates to 19 A, at 45 °C to 18.5 A, and at 55 °C to 17.5 A (–). The terminals accept solid or stranded conductors from 2.5 mm² up to 50 mm², which covers everything from standard 2.5 mm² lighting circuits up to 50 mm² feeders for sub-distribution.
It's a standard SENTRON catalog line, so it's not a niche or legacy part that's hard to find.
Key specs at a glance for the panel builder
Insulation voltage rated 690 V, overvoltage category IV, pollution degree 3 — this is a robust breaker for the main distribution point, not just a final-subcircuit device. Shock resistance tested to 30 g, at least 3 impacts of 11 ms duration. The locking device has an integrated locking slide, lockable by lock, wire seal, or cable ties. Infeed at box terminal, and the supply cord position is any — no orientation restrictions when wiring.