The 40 A rating at 35 °C is the headline figure; at 40 °C ambient it derates to 37.56 A, at 50 °C to 34.96 A, and at 55 °C to 33.6 A, per the manufacturer's published curve. The 5SY6540-6 occupies 2 modular width units (36 mm) on a DIN rail, with a depth of 76 mm and an installation depth of 70 mm. It mounts in any position, and the terminals are combined (top and bottom) for feed-through wiring.
The 5SY6540-6 is certified to IEC / EN 60898-1 and IEC / EN 60947-2, and also carries UL1077 recognition. The sealable feature (tamper-evident cover) is available for installations that require lockout or anti-tamper compliance. The product designation per EN 61346-2 and IEC 81346-2 is letter code F — the standard symbol for a protective device in functional plant documentation.