Why choose the 3 kW fanless step over the 4 kW?

Somewhere between 3 kW and 4 kW the FSB frame has to start moving air. The 3 kW step stays on natural convection - 425x180x134 mm, no fan, no filter to clean, no bearing that wears out and nothing that can be blocked by lint on a packaging line. If the section really needs no more than 7.7 A continuous (15.4 A for 3 s at 200% overload), the fanless version removes an entire maintenance item from the machine. The 4 kW variant exists for sections that need the extra 2.5 A of margin and is willing to take the fan and the 35 mm extra housing depth.

How does the drive join a PROFINET line without extra switches?

On a line with several distributed drives, the AF0 variant daisy-chains directly: two M12 D-coded ports on each drive, power and PROFINET on one hybrid cable, and the network travels the length of the machine without a single field switch. Wrap the ends back and the line becomes a ring, so one cut cable degrades nothing. PROFIsafe rides the same two wires, and the predefined TIA Portal macros plus function blocks map the drive into a SIMATIC controller in a fraction of the manual commissioning time. Sections that will never join a network take the AB0 or AA0 variant of the same 3 kW hardware instead.