At 20 A, that's a magnetic trip threshold between 100 A and 200 A instantaneous. Rated for multi-phase operation up to 440 V AC maximum, and single-phase at 250 V AC. DC rating is 72 V maximum — usable on DC control circuits but only at that voltage ceiling.
Touch protection is integrated. Overvoltage category III and degree of pollution 2 — standard for fixed-installation distribution boards inside buildings.
The closest functional peer is the 5SL4363-7 — same SENTRON series, same C-curve, same 20 A rating, same 7.5 kA breaking capacity per EN 60898, same 72 V DC max, same mechanical endurance. The critical difference is pole count: the 5SL6420-7RC is 4-pole (4P) at 72 mm wide (4 MW), while the 5SL4363-7 is 3-pole (3P) at 54 mm wide (3 MW). If your panel was laid out for a 3-pole breaker, the 4-pole version will not drop in without rewiring and a wider DIN slot. The 4-pole is the correct choice when the neutral must be switched or when the circuit requires four protected poles (three phases plus neutral).