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I have two devices which need to talk to two controllers about 60m away in the garden.One uses RS485 and one uses CAN.

I have to run armoured CAT6 for this and wondering if I can use the same run for both devices by using different pairs?

Would CAN and RS485 degrade earch other?

Update after receiving answers:

I will run it over the same cable. If it struggles then I will bite the bullet and run a second cable. Given the cost of the project there is no point in being silly about this rather minor expense :)

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    \$\begingroup\$ Will there be anything else in the cable? Will there be ground reference via the cable as well? Is it powered via the cable too? \$\endgroup\$
    – Justme
    Commented Apr 22, 2022 at 21:07

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If it works separately, the crosstalk between pairs should be benign enough to allow them to work together. If you can buy for a similar price, CAT.7 as often used in installation these days, has individually shielded pairs – the isolation between these is impressive.

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  • \$\begingroup\$ thank you. I can only get CAT5e or CAT6 in armoured. I know they're both low-speed (just sending back solar panel metrics) so not very chatty. \$\endgroup\$
    – Crispin
    Commented Apr 22, 2022 at 21:32
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I second Marcus about (CAT7) S-FTP cabling = individually shielded pairs. Why do you keep insisting on armoured cable? That's exotic and expensive. Have you considered burying a plastic pipe, and pulling some less exotic cable through that pipe? This solution might turn out to be cheaper than an armoured cable, and would allow you to add or replace a cable someday down the road = is future-proof.

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  • \$\begingroup\$ Be sure your capacitance is in tolerance before you build it. I do not know what else is on the system. \$\endgroup\$
    – Gil
    Commented Apr 23, 2022 at 5:28
  • \$\begingroup\$ @Gil you possibly mean pair impedance. The impedance of CAT5/6/7 is between 100 and 110 Ohms. The nominal impedance of CAN is 120 or 125 if memory serves, and RS485 is thereabouts as well. That's very little difference from CATx. In fact and in my past practice, CATsomething cabling (esp. CAT7) is about the best cabling that you can wish for balanced transfers such as RS485 (up to 10 Mbps) or CAN - although there are dedicated single-pair shielded high-speed cables for those busses as well, with just the right impedance. See LAPP Kabel or Helukabel or possibly Belden. \$\endgroup\$
    – frr
    Commented Apr 23, 2022 at 5:35
  • \$\begingroup\$ I was not worried about the impedance it is within range for both. Wires have capacitance, the longer the wire the higher the capacitance. Even twisting them changes the capacitance. Regardless of the signal it also has to overcome this. Capacitance in cables is usually measured in pf/m (pico farads per meter) or pf/ ft (picofarads per foot). The lower the capacitance the better the cable performance. \$\endgroup\$
    – Gil
    Commented Apr 23, 2022 at 23:42
  • \$\begingroup\$ I could use use conduit and cat6/7 runs. The costs are roughly the same but the SWA is easrier as I can drap it through the bushes and not worry about dammage. Conduit I think might, after a while, call victim to teeth. As for rs485 over CATx cable - I have seen many posts where people have used it 100-150m without issue. My variation is the inclusion of CAN in the same cable, different pairs. I think I will run amoured, if it does not work, run a second armoured. It's not that much money when compaired to the whole project :) \$\endgroup\$
    – Crispin
    Commented Apr 24, 2022 at 11:34
  • \$\begingroup\$ @Crispin: RS485 drives the wires typically at around 5V differential, and the nominal detection threshold is 200 mV Schmitt trigger (practical transceivers tend to detect at about 130 mV). AWG23 means about 67 milliOhms per meter single wire (twice that for a pair). For a bus impedance and termination = 100 Ohms, the maths boil down to about 18 km of reach, considering just resistive losses. At higher baud rates, this gets shorter. Teeth? You should bury the cable or conduit to protect it from the sun = UV. Even a few cm of dirt goes a long way. \$\endgroup\$
    – frr
    Commented Apr 25, 2022 at 6:41

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