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I am wiring a ceiling fixture. There are three cables in the ceiling box. Only one of the cables has power. This cable powers the others that go on to power switches to ceiling fixtures in two separate rooms. I have found the live wire in the one cable and separated it from the neutral. I would like to know how to determine polarity of the other wires. This house was built in 1922 and on this circuit the cables and wires are cloth covered. I have used a "klein voltage tester" to determine the hot wire. In order to connect the others, how do I determine polarity? Virginia, USA Thanks!

  • So, I've thought quite a bit about this. If I disconnect the light fixtures in the two separate rooms fed by this cable, and do trial and error I can determine the black and white wires at the fixtures without damaging the fixtures? – SLK Jul 24 '14 at 13:56
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The wires themselves don't have polarity, that only exists within an outlet based on it being wired correctly, or reversed (hot/neutral reversed).

So essentially you just need to identify the hot wires and the neutral wires, and if you maintain this correctly throughout all of the wiring and correctly wire up your outlets, then polarity will be correct.

Non-contact testers are good for determining if there is any power on, but not perfect for finding the hot wire - sometimes neutral wires will give false positives if there is a hot wire in close proximity.

The best tool to use is a multi-meter. The neutral and ground should read 0 (or a very low number), and hot to neutral or hot to ground should give you 120V (assuming your are in North America).

A standard outlet tester will tell you whether the polarity is correct or reversed. If it's reversed, then you just swap the hot/neutral wires.

  • What I do to reduce the false positives on the neutral is to carefully place my other hand on the wire a few inches away from where I'm testing with the non-contact tester. – Brad Gilbert Jul 23 '14 at 12:38

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