The Siemens 5SL4320-8CC is a SENTRON 5SL miniature circuit breaker — 3-pole, D-curve, 20 A, breaking 10 kA at 400 V AC. Rated for residential and infrastructure panels, but the 10 kA SCCR and overvoltage category 3 rating let it serve light commercial sub-distribution too.
Compared to the 5SL6606-7YA (4-pole, C-curve, 6 A, 6 kA), this 5SL4320-8CC is a different animal: three poles instead of four, D-curve instead of C, and 20 A instead of 6 A. The 5SL6606-7YA also switches the neutral; this unit does not. If your panel was laid out for the 5SL6606-7YA, the 5SL4320-8CC will not drop in — different width (54 mm vs 72 mm), different pole count, different curve. No rewiring shortcut here.
Mounts on DIN rail — any position, thanks to the any-position rating. The 54 mm width (3 width units) fits standard distribution board cutouts. Wire range 0.75 to 25 mm², so it accepts both control-circuit tails and feeder conductors.