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Can_Bus wiring with CAT6

2617 Views 6 Replies 6 Participants Last post by  Frigzy
Hi guys, I am wondering if I can get your insight on how to wire the CAN_bus network in my car. I have read a lot of different information about stub length and other factors so I am wondering what has worked for you.

One option that is very appealing is to use CAT6 cable to carry two CAN channels throughout the car. With CAT6, It Ould be convenient to use the RJ45 connector and just bring them all to one central point but that greatly extends the lengths of the cables. So would it be better to run a central line and then branch off to each component, or snake the cable from component to component to minimize the stub length. What do you all suggest?

For reference, the car in question has the following can enabled components, roughly in order from rear to front.


Thanks for the input!
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Not sure it's rated for CAN, but just make sure it has a shield, and that you ground it to the device you're using to communicate with.
CAN is meant to be a single long bus not a star configured link. When you run wiring the idea is to create short taps off the main set of wires. It isn't meant for each thing to necessarily be connected all at the same point. Keep the taps short if you can help it.

CAT6 wiring will likely be fine. What you really need are twisted pairs of wires and you get that with ethernet cabling. Shielding isn't strictly required but would not hurt for CAN. CAT6 is unlikely to be shielded as shielding very fast signals like ethernet can cause reflections and signal issues that you just don't want.
As others said it will probably work.

But keep in mind that since it is not designed strictly for CAN, it probably won't have the correct characteristic impedance and so you should probably keep your stubs shorter than the spec allows.

In general, you should keep your stubs as minimal as possible. As Colin mentioned, CAN isn't designed for a star topology and though it is technically possible to do if all your arms are less than the stub length spec (1 meter if I remember right) I certainly wouldn't do that if using CAT6 cable or other cable that is not specifically designed for CAN.

Edit: Looks like CAT6 cable impedance is 100 ohm. That's close enough to CAN (120 ohm) that you can probably ignore my warnings for the most part.
To be honest, I would personally put the drive inverters on a dedicated CAN bus, and use properly rated wire. You really don't want errors or dropouts on that bus.

The rest of the stuff is less critical.
The main problem I see is that CAT6 cable and connectors cant handle the constant vibration and mechanical shock associated with normal driving.

You will constantly be tracing down loose pins and broken wires after the first month.

I strongly recomend sticking with DOT/Automotive rated wires and connectors.

Automotive wire is more flexible (vibration resistant)

It's easy to identify automotive rated wire , it will be rated at 32 volt

The wire is insulated up to 300 volts but will be listed as 32 volts for two reasons.

1. An old style 24 volt alternator maxes out at 32 volts.

2. They dont want people using this wire in their houses because it does not meet residential code. ( wire and insulation are not rigid enough )

Just remember that there is a reason the automotive industry went through the trouble of creating their own connectors.

I like the Bosch EV-1 series.
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CAT6 will work fine on your desk, less fine in the real environment due to poor mechanical properties of cable and, mainly, connectors. RJ45 is a huge pain in the automotive world. There is absolutely no way it will pass any of vibration/environmental tests. Your best bet is using regular automotive wire (GXL / TXL / SXL) and hand-twist it. CAN is not picky at all. Don't forget to terminate at both ends (don't terminate at stubs). Use any appropriate automotive connector for the connections.
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