I'm working on a project with a DC motor that runs in both directions. If the motor ran only in one direction, I'd use red/black for positive and ground, but as they reverse, there isn't a consistent positive or negative terminal. I understand that wire color isn't the most important thing, but I'm wondering if there is any standard or convention, even if it is weak.

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    \$\begingroup\$ I tend to default to orange and purple as commonly available wire colors that aren't really established standards for anything in particular, but it's a matter of opinion. \$\endgroup\$
    – Hearth
    Feb 22, 2021 at 4:22
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    \$\begingroup\$ The great thing about standards is there are so many to choose from... \$\endgroup\$
    – Ron Beyer
    Feb 22, 2021 at 4:26
  • \$\begingroup\$ As in DMM probes Red=+, Blk= - Logically you may reverse anytime depends on CW or CCW \$\endgroup\$ Feb 22, 2021 at 4:29
  • \$\begingroup\$ @Hearth I was going to default to something similar if I can't find better. TonyStewartSunnyskyguyEE75, there's no consistent +/-, so I don't think red/black works. \$\endgroup\$ Feb 22, 2021 at 4:32
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    \$\begingroup\$ well, red/black are pos/neg for the forward direction; they are actually IEC endorsed for DC supplies. The only nitpick is that being them possibly reversed there could be a cabling conundrum where someone pick your motor ground as a ground for something else. So the red/blk pair should only, in principle, for unswitched raw power supplies. It's mostly a project/customer requirement thing \$\endgroup\$ Feb 22, 2021 at 7:24

1 Answer 1


As the motor is reversible, I'd be inclined to use two wires of the same colour. This helps emphasise that you can't make any assumptions about them.

One thing I've learnt in years of engineering is that a colour scheme that's obvious to one person is anything but to another, unless it's mandated by some standard like mains wiring, where black is ground on the European side of the pond, and hot on the US side.

  • \$\begingroup\$ This is a good point. I would do this, but I'm not using keyed connectors, and so I could get the motor running opposite the intended direction. \$\endgroup\$ Feb 22, 2021 at 15:39

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