Old House Ceiling Light:wired To Black Leads Only, White Leads Wired Yogether - Electrical - DIY Chatroom Home Improvement Forum

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Old 10-06-2010, 09:02 AM   #1
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old house ceiling light:wired to black leads only, white leads wired yogether

The wiring in our house is quite old, and not to the current code. I want to replace an old fluorescent ceiling fixture with a modern "no-ballast" one.
There are 3 cables (white, black and ground) coming into the box. The 3 white wires are all wire-nutted together; the lamp is wired between one pair of blacks and the other black wire. Ground wires are grounded (actually, only two are). One of the black leads is still live though the switch is OFF.
Should I install the new light the same way as the old (after shutting down the breaker)? Thanks a lot!


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Old 10-06-2010, 01:33 PM   #2
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Have you opened the box containing the switch? A single cable with black/white/ground and no other?

I am guessing that your setup is, in effect, switching the neutral. You have supply going to one wire of the fixture. The other wire of the fixture is attached to the black wire going to the switch. The white wire from the switch is joined with the other white wires at the fixture box. At least, this is my guess.

My assumption is that this would not meet code if doing it today. I have always assumed that the preference to switch the hot side is to avoid having power at the fixture when the switch is off. Furthermore, I assume that this is considered preferable so that one does not shock oneself if working at the fixture and assuming that there is not power because the switch is off.

A lot of guesses and assumptions. Hopefully, you can confirm this theory with a volt/ohm meter.


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Old 10-06-2010, 02:11 PM   #3
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Which black wire is live when the switch is off?

Which black wire goes to the switch?

How is the third black wire connected?

Take the black wire to the switch and connect it to the light fixture black wire.

You want to take the white wire that accompanies the black wire to the switch and connect this to the hot black wire and also the third black wire.

Connect the white wire from the new fixture to the other two white wires (all wire nutted together).

Mark both ends of the white wire attached to the switch using black tape or stain (or Magic Marker ink).

Connect all the ground wires together including that to the fixture. If the fixture doesn't have a ground wire, cut a piece of bare wire (a pigtail) to connect the cluster of other ground wires to the fixture.

Incidentally if you ignore the above and take the two wires that used to be connected to the old fixture and connect them to the new fixture then it would still work.
The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.

Last edited by AllanJ; 10-06-2010 at 02:16 PM.
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Old 10-07-2010, 02:21 PM   #4
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Thanks, oberkc and AllanJ, for the responses. I can't digest it all now, and don't have time for the light, right now - but, thanks!
michael13 is offline   Reply With Quote

3 cables in one fixture , old wiring , white leads wire nutted , wired to black leads

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