The Siemens 5SL6420-6 is a 4-pole SENTRON miniature circuit breaker with a B tripping characteristic, rated 20 A at 400 V AC and a breaking capacity of 6 kA per EN 60898 and IEC 60947-2. B-curve means the magnetic trip activates between 3 and 5 times rated current (60–100 A for this 20 A unit), making it a good fit for resistive and general-purpose loads in residential and infrastructure panels — not for motor starting where inrush would nuisance-trip it. For higher fault-current environments (industrial mains), a higher-rated 5SL6 variant would be needed.
Temperature derating — the real-world current limit
At 30 °C ambient the 5SL6420-6 carries its full 20 A. At 40 °C it derates to 18.79 A, at 45 °C to 18.6 A, and at 55 °C to 16.8 A. If the panel runs hot — say 45 °C inside the enclosure — the circuit must be loaded to no more than 18.6 A continuous, not the nameplate 20 A.
The 72 mm width (4 MW) is standard for a 4-pole MCB in this class; it occupies four adjacent 18 mm slots. Sealable design means the factory or installer can apply a wire seal to the toggle to prevent unauthorized operation after commissioning — useful for landlord-tenant submeters or critical infrastructure panels.