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I’m building a CAN bus interface for automotive use, connecting from the OBD-II port (under the dash) to a remote enclosure containing an ESP32 + MCP2515 module, with a total cable length of ~12 feet (including short stubs at both ends).

Is 20 AWG overkill for CAN_H/CAN_L (twisted & shielded or twisted & sheathed)?

I typically use 20–22 AWG in automotive projects (my connectors support both), but I’ve seen 24 AWG and smaller used in commercial CAN cables. What’s appropriate for a 12 ft run?

I lean toward 20 AWG for robustness and to accommodate unknown installation variables.

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  • \$\begingroup\$ It mostly depends on if in the cable, you are doing 1) pure signals 2) signals + supply for secondary in a galvanically isolated setup, or 3) signals + main device supply. Some of the super expensive M12 CAN twisted wire/shielded cables intended for 2) or 3) have different wire thickness for the supply cables vs the signal cables (and individual shielding). In most situations this is way overkill however. \$\endgroup\$ Commented Nov 5 at 9:48

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CiA 303-1 - CANopen physical layer recommends these values:

Bus length [m] Length-related resistance [mΩ/m] Cross-section [mm2] Bit-rate [kbit/s]
0 to 40 70 0.25 to 0.34 1000 at 40 m
40 to 300 <60 0.34 to 0.6 ≤500 at 100 m
300 to 600 <40 0.5 to 0.6 <100 at 500 m
600 to 1000 <26 0.75 to 0.8 <50 at 1 k m

In your case at 12 ft (<4 m) the recommendation is 0.25 mm2 (24 AWG) to 0.34 mm2 (22 AWG).

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    \$\begingroup\$ Upvoted for spec data. By the same token there appears to be no reason not to use AWG 20 where physical robustness is important. \$\endgroup\$ Commented Oct 31 at 7:39
  • \$\begingroup\$ @Spehro'speff'Pefhany I agree, unless the cable harness becomes too stiff. \$\endgroup\$ Commented Oct 31 at 9:22
  • \$\begingroup\$ @Velvet CIA publications seem to be gated. Are there any good publications in layer 1 standards or recommendations I can access for free? \$\endgroup\$ Commented Nov 4 at 6:46
  • \$\begingroup\$ You can check out vendor application notes (NXP, TI, and others). Some of them are excellent that dive into CAN details. For example AN96116 chapter 5.3. \$\endgroup\$ Commented Nov 4 at 7:20
  • \$\begingroup\$ @DNR2ME These publications are free but you might have to register on the site to get access to downloads. CAN in Automation is a non-profit organization and it's called CANopen because it really is open - the standards are available free of charge. \$\endgroup\$ Commented Nov 5 at 9:50

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