The 5SY4440-6KK11 carries a 40 A rated current at 35 °C ambient. Above that, the thermal trip element derates: 38.4 A at 40 °C, 37.6 A at 45 °C, 36.76 A at 50 °C, 35.92 A at 55 °C, and 35.04 A at 60 °C. For a panel running hot — say 50 °C inside the enclosure — the continuous load limit drops to about 36.8 A, not the faceplate 40 A.
Breaking capacity — dual-rated for the standard in use
The higher figure under 60947-2 reflects the standard's allowance for the part's actual performance in a defined upstream impedance. For a site engineer coordinating with an upstream 25 kA rated MCCB, the 15 kA figure gives more headroom in the selectivity study. The B-curve restricts let-through energy to Energy Limitation Class 3, which helps downstream components survive a fault.
Panel fit — 4 MW, quick assembly
Installation depth is 70 mm; total depth 76 mm.