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I am working on a double leaf bascule bridge and installing a PLC I/O rack on the farside. The power transmission between the two piers (nearside and farside) is via a single submarine cable (installed 1987). Unfortunately, the submarine cable is made up of #10 AWG xhhw-2 control wires and no ethernet cables. Would it be possible to use 8 individual #10 AWG wires to make up the "4-pair" cable required for PLC communication? I would like to avoid wireless communication, and modifying existing/installing a new submarine cable is not an option.

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  • \$\begingroup\$ Not for anything resembling Ethernet, no. \$\endgroup\$ – brhans Feb 12 at 17:19
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    \$\begingroup\$ I'm going to say "probably not", but...What is the cable length? Are the wires you have twisted in pairs? What Ethernet rate do you want to try to achieve (10 Mbps is much easier than 10 Gbps)? \$\endgroup\$ – The Photon Feb 12 at 17:21
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    \$\begingroup\$ You might be able to get a ethernet over powerline link running across wires like that. \$\endgroup\$ – Voltage Spike Feb 12 at 17:47
  • \$\begingroup\$ Does it have to be ethernet? RS-485 might work well in this situation, if you can use a PLC that supports it. \$\endgroup\$ – Nate Strickland Feb 12 at 18:36
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This almost certainly won't work.

What makes twisted pair work for high speed data transmission is not just the diameter of the conductor, but also that the two wires in each pair are kept a constant distance apart along the length of the cable.

Wires in Cat-5 pairs are also twisted together, but this is done more to reduce cross-talk and interference (because the interference in one part of the twist will cancel the interference in another part of the twist) than to enable high-speed transmission in the first place.

So if your wires are not kept at a constant, controlled separation center-to-center, they won't provide a good path for high-frequency signalling. And if they aren't twisted together in pairs, they will be subject to cross-talk and interference.

As far as I can see, the "XHHW-2" spec is about the chemical and water-resistance of the insulation, and will have very little to do with how well these wires can carry high-frequency signals. The dielectric constant of the insulation will affect the characteristic impedance of the wire pair, but this effect could be compensated for with a matching circuit at each end of the cable if necessary.

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  • \$\begingroup\$ Thankyou for response, I just found out that the Submarine cable does have Coaxial cables (RG-11) originally used for CCTV. Would a Ethernet over Coaxial Converter work? \$\endgroup\$ – JCR Feb 13 at 19:37
  • \$\begingroup\$ @JoshRinehart, I can't say without seeing the datasheet for the coaxial converter, also knowing the length of the cable and the data rate you're targeting. (and even then, I'm not an expert on Ethernet installation). One issue will be that your video cables will be 75 ohm type while your converter might be designed for 50 ohm cable. \$\endgroup\$ – The Photon Feb 13 at 19:49

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