Thanks for that info. Does anyone make a convertor with an RJ45 female socket in, so that the RJ45 cable from the VFD can be plugged into that?

So the chain would be:
VFD > RJ45 cable > [female RJ45 in / convertor box / cable out] > RS485 PCI card in PC.

Otherwise, it seems a bit messy. Using the £16.99 RS solution with the block terminals it would seem that I have to strip out one end of the RJ45 cable, and connect the 2 signal pins. Is that correct?

Also the manual states that resistors are required at each end of the cable, with an note on watching the impedances. Do these solutions above include that feature already?