We're thinking about using a modbus over RS485 line to communicate w/ a mobile device, but its original power cables work along a "slide rail" in order to allow its movement. Our doubt in fact is how to connect the device with its master in a reliable and preferencially cheap way. Is using a simple shielded cable a good idea?

 

A few years ago we implemented a DH485 system in a quarry over long distances. If I remember correctly the cable, when above ground, was in conduit. During thunderstorms it was a fair bet that the quarry would lose one or more (sometimes all) of the isolated link couplers that provides electrical isolation between the port on the PLC and the rest of the network. There was a great deal of work to provide good grounding, but good grounding in a rock quarry is virtually impossible. The lead engineer put surge suppressors at each DH485 node and this seemed to significantly reduce, if not totally eliminate the loss of the isolators. So I would recommend consulting your PLC vendor (I assume you are using PLCs) and ask that they specify good surge suppression for your network. I hope this helps.

 

We had outdoor and underground comm cables and trouble with each thunderstorm. Surge suppressors and screen didn't help much. we solved the problem finally with fibre glas cable and optical converters.

Walt