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I need to run two logic signals around a vehicle, so for good measure, regardless if its overkill or not, I want to use a shielded single pair wire for that job. At one point it should be crimped to and go through a connector like in this sketch attached.

Few questions - going by the grounding the shield on one side only - is the sketch showing the proper approach? Also, the paired cables will each carry its own logic signals - is there a chance of noise or interference inside of the shield, between those two cables and two separate signals?

enter image description here

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  • \$\begingroup\$ It doesn't look at all like a reliable solution to me (especially given the automotive environment). \$\endgroup\$
    – Andy aka
    Jan 11, 2022 at 11:05
  • \$\begingroup\$ The question of whether or not a ground loop will be a problem depends entirely upon the circuits to which these wires are connected. However, that information does not appear in your question. \$\endgroup\$ Jan 11, 2022 at 14:21

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A shield is not part of either signal or return currents. It is part of or an extension of the chassis. So it should be bonded to the chassis thoroughly at both ends.

If the two wires inside your shield are independent single-ended signals, you invite interference, not because they are close as such, but because their respective intentional return current wire is very far away. As a result, return current will be encouraged to flow in the other signal wire or in the shield, both of which is bad.

Solution: Add an additional signal return wire inside the shield, that both signals can use as return.

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  • \$\begingroup\$ This is the part that confuses me - grounding on one side vs both sides, and in many topics on automotive wiring and shielding, many people wrote that these cables should be grounded only on one end to avoid ground loops. Also when you mention return signal return wire - not sure what is that referring to. The current setup works when I test it on my workbench, of course inside a vehicle powered by battery/generator is a different story, are you referring to cable length and signals (both coming from arduino pins) traveling distance? The cable will be approx 2 or maybe 3m long. \$\endgroup\$
    – Varonne
    Jan 11, 2022 at 11:02
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    \$\begingroup\$ @Varonne It is unfortunate but there is a lot of misinformation around. Ground loops are only a problem for signal currents. But as I wrote, the shield is not part of any signal circuit. The shield is chassis. When you omit the return wire in the cable, you will form a large loop though (call it ground loop if you want). That's why you add the return wire close to the signal wire inside the cable. What that return wire is depends on your signal. Most likely it is signal ground when signals are ground-referenced single ended. \$\endgroup\$
    – tobalt
    Jan 11, 2022 at 11:40

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