If I'm not wrong, RS485 uses current loop for signaling.

So it should be quite immune to interference and
a twisted-pair cable will not give as much improvement
as with voltage signaling.

I believe UTP cable should be good enough.

Regards,
Peter Tiang


> Hi all,
>
> I want to interface my PIC project with the outer world using a low
> baud rate RS485 interface (MAX488 full duplex, slew rate limited).
> The maximum cable length is approx. 100 meters (333 feet) and could
> be routed near other equipment which may cause interference on the
> cable.
>
> My question is, is it absolutely nessary to use a Shielded TP cable
> instead of the more common UTP cable (CAT5)?
> I was wondering this since RS485 is already pretty solid especially
> combined with low data rates (2400 bps).
>
> Thanks!
>
> Bye,
>
> Daniel...
>