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I'm looking to build a distributed PLC system with up to 20 devices spread throughout a building, controlling lights, HVAC, irrigation, security, etc, and want recommendations on what connector to use for CAN and DC power.

The power (24VDC, 1W/device max, 50mW/device typical) and CAN will go in the same cable. While M12 connectors seem to be "common" for CAN, they're not very easy or cheap to buy.

RJ-45 looks like the all-around cheapest option and the quickest to terminate cables, but I'm concerned about reliability and power handling with 20-40 plug/socket pairs in series, before you even consider copper loss and unclean/non-office environmentals like heavy dust and insects. I could use two pairs for power to improve matters but it's still marginal.

I could use Molex or Camden style power connectors but they have other issues, like the time taken to terminate cables and increased likelihood of transposed conductors.

What standard connector, perhaps commonly used for building management and/or industrial automation, am I missing? I don't need 1Mbps; 100-200kbps should be plenty so impedance control isn't real important.

Background: I would like to avoid a star topology and the central switch or controller that it implies. Running one CAN cable adjacent with the power distribution cables also reduces the installation cost dramatically, especially for retrofits.

Edit: does anyone know what is used in vehicles? They'd have to be plentiful and reliable.

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  • \$\begingroup\$ Are you developing this for a specific industry customer or for an in house solution? Many industries have more rigid specifications for connectors used. I completely sympathize with you about the M12 cordsets and receptacles being difficult to source \$\endgroup\$ – crasic Dec 8 '15 at 5:53
  • \$\begingroup\$ Initially it will be just my house but with a view to getting them properly accredited/certified and doing a small production run. So I care about AU, US and probably EU safety+EMI/EMC standards, and I care that they will work reliably in a roof space for 20 years. \$\endgroup\$ – William Brodie-Tyrrell Dec 8 '15 at 6:16
  • \$\begingroup\$ Use simple screw or spring type contacts connector, you need to use twisted pairs for CAN with respective characteristics impedance. As for wire terminating and other stuff is always welcome to do it, CAT5 is too thin and even more complicated for crimping. \$\endgroup\$ – Marko Buršič Dec 8 '15 at 9:34
  • \$\begingroup\$ Maybe look at what connectors the PLCs have and take it from there, since having different connectors all over the place isn't helpful either. \$\endgroup\$ – Lundin Dec 8 '15 at 12:31
  • \$\begingroup\$ the commercial PLCs I've seen seem to either have screw-terminals (error prone) or RJ45 (no good for power). \$\endgroup\$ – William Brodie-Tyrrell Dec 8 '15 at 21:13
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CAN In Automation recommends 9 pin D-sub connectors with a specific pinout. These aren't easy to get two wires into each pin for daisy chaining, so you might need to use a field rewirable type like this Phoenix Variosub rewirable D-Sub Connectors.

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  • \$\begingroup\$ What's the pioint of using DSUB connector with screw contacts? HAve you seen DSUB 9 connectors in your car's electronics? You can use a screw connector directly without DSUB 9, less troubles. A good cable is liycy 2x2x0.5mm^2 or 2x2x0.75mm2, you can put CAN and power together. \$\endgroup\$ – Marko Buršič Dec 9 '15 at 17:16

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