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My contractor removed multiple ceiling fans and I am replacing them with new fans. There is a red, black (hot) and white (neutral) wire. Is it normal for only the red wire to have 120V AC? An AC meter reads 18V across the black and white wires: 120V AC across the red.

Updates

Good questions are appreciated. Updates will be edited here to respond to good diagnostic questions:

  • This non-standard wiring was observed in 3+ fixtures
  • Each fixture is controlled with a single switch
  • All fans for this discussion are ceiling fans
  • Black to white AC potential is 18V
  • I believe that I have not mistaken green for black

Current configuration: Wired and powered new fans with Red wire and is controlled by a switch in the wall

It is puzzling that the Black-White potential is anything other than 120V

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    Is the black on a switch?
    – mmathis
    Aug 24, 2017 at 18:30
  • Are you sure the black is black and not a very dark green? I've seen some wire where the green is so dark it almost looks like black in certain lighting.
    – BillDOe
    Aug 24, 2017 at 18:35
  • What kind of fan do you have: ceiling fan, sports fan, duct fan, ...?
    – Niall C.
    Aug 24, 2017 at 18:39
  • Can you look inside the switch box for that black wire? Aug 24, 2017 at 23:39
  • You might take apart a switch and see if the other end of the blacks is in there capped off,. Sounds like /3 wire since there is a red. This would have been used with a light and fan with a dual controller such as m.grainger.com/product/… 18v is just floating - it's not real add a light bulb in the circuit and it will be 0v
    – Tyson
    Aug 25, 2017 at 0:06

1 Answer 1

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I think the red wire is to control the attached light via a switch.

Try the link below for more info.

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  • I red the same article when wiring. There is only one single switch per outlet
    – gatorback
    Aug 24, 2017 at 23:09

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