Multiple RS-232 Lines


Thread Starter


Is it possible to run multiple RS-232 lines within the same 35-wire cable. I am concerned about crosstalk and parasitic capacitance. The cable would be approx. 30' max. I have to talk to set of 10 different instruments across the room and I don't want to run 10 bulky cables. Wireless is not an option due to cost. Thanks to anyone who can reassure me that I won't be seeing garbage on the PC end!

Steve Myres, PE

You can get multiconductor cable where each set of conductors is twisted and individually shielded and drained. If you use this type of cable (which will admittedly be bulkier than a cable with only an overall shield), I think you'll be OK.

Another option would be to add an RS485 converter to each of the devices and serve them with a single comm bus, or to use a multiport RS232 breakout box at the remote location.

I like the multiple twisted pair idea. I just ordered some from Newark (12 pairs and only 0.460" O.D.) that is specifically for RS-232 applications. It's only $140/100' which is less than I'd spend building 10 different cables. I won't be on-site to install until next month but I'll definitely let you know how it went. Thanks for the help!

Lynn August Linse

As long as all wires are connected, you should be Ok. The main problem you'll see is if you disconnect or power down just 1 end of the cores to 1 of the 10 instruments, the other end will see serious garbage. Depending on the core arrangement, you could even see a 99% good-looking copy of what one of the other lines is sending.

Best Regards

Lynn August Linse, [email protected]
3 Rue Monet, Foothill Ranch CA 92610
Ph: 949-300-6337 Fx: 612-677-3253