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The wires coming from my wall A/C unit are not color coded. The unit was hard wired and is being replaced. the wires that are coming from the a/c unit into the power connection box are not colored . both are stranded copper straight out of the plastic sheathing. the connection wire IN the power box ARE BOTH BLACK ....just seems weird to me. Any suggestions?

  • Can you post photos of the wires in question and of the A/C's nameplate? – ThreePhaseEel Aug 29 '17 at 0:25
  • I'm not sure we care about the old unit (although we could). Is the new AC unit going to be hardwired, or are you putting in an outlet? Do you have a meter or power tester? What gauge is the wire IN the box and what size is the breaker supplying power to it? – noybman Aug 29 '17 at 1:23
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    Is the unit operating on 120 V or 240 V? What is the size of the unit in BTU/h? – Jim Stewart Aug 29 '17 at 1:44
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Nothing weird about that. Being hardwired, most likely it's a 204V air conditioner.

Wire colors are to distinguish wires.

Sometimes two wires are just instances of the same thing. If you swap the wires, everything works.

  • the two "Messengers" in 3-way switch circuits
  • 2/3 phases in NYC or Euro style mains power, e.g. 208V or 388V to an A/C unit
  • The two "hot" poles in 240V wiring of split-phase North American power

The wires are interchangeable and it's useless to distinguish them from each other. But very useful to distinguish them from other wires with other duties. Therefore, no reason to waste a color.

However, 120V line cords are sometimes ribbed

That said, cheaper line cords, e.g. used on 120V lamps, often have no inner colored insulation, just an outer sheath that can be split. They distinguish sides with one side of the cord being ribbed. The ribbed side is neutral. However in the above cases, it makes no difference.

Why do you expect them to be red-black?

Because of the stock colors found in multi-conductor cable. They make each one a different color because they have no idea what your use will be.

  • /2: Bare Black White
  • /3: Bare Black White Red
  • /4: Bare Black White Red Blue

That makes sense. Why stock several color combos of /3, when we can just tape the wires to mark them different colors?

For instance, white/gray=neutral (as well as green/bare=ground) are the only mandatory colors. Other than that, anything goes. In house wiring, the convention of Black=always-hot and red=switched-hot works reasonably well for simple boxes. But on a complex box it can get out of hand really quick, and that's when you want to do things like tape the messengers yellow, tape the second hot and neutral brown/gray, etc.

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