12:54AM | 05/02/07
Member Since: 05/01/07
2 lifetime posts
I'm hooking up a ceiling fan where an old light fixture used to be.

When I pulled the coiled wiring out of the top of the box so I could go about reinforcing it, I noticed something strange about the existing wiring.

There were TWO lines running into the box. From these, one line's black wire was connected to the other's white! Also, the light's black was from one line and the white from the other. The grounds were twisted together.

I don't understand this. There is only one switch and one fixture in the room. The switch activates the one fixture and there are no other connections that I know of.

Why would this be done? What should I do?


04:00AM | 05/02/07
Member Since: 04/25/05
1915 lifetime posts
What you are describing is Switch Leg Wiring.

Here is a drawing of it.

When work ing with cable you are restricted to the colors and all will come with one white wire.

It is correct except the white wire should be "remarked" at each end. This is usually done by putting a piece of black tape on it.

The idea of doing it this way is that the light fixture will always be connected black to black and white to white.


06:12AM | 05/02/07
Member Since: 04/25/05
1915 lifetime posts


06:40AM | 05/02/07
Member Since: 09/17/02
524 lifetime posts
Perfectly mormal switch loop wiring. leave alone and connect your fan to the same wires as the light was connected to.


07:14AM | 05/02/07
Member Since: 04/25/05
1915 lifetime posts
I forgot that this was for a ceiling fan.

With a switch leg you have a couple of options. One is have both the light and fan controled by the switch. Then you use the pull chain to control each one individualy.

In that case the fan (black) and light (typically blue) are both connected to the wiring black, just like the light was.

But there is another option that I like better.

The fan (black) is connected to the supply hot. So it powered all the time and controlled by the pull chain.

The light (blue) is connected to the switch leg black. And leave the light pull chain on all the time. Then the light is controlled by wall switch.


01:20PM | 05/02/07
Member Since: 05/01/07
2 lifetime posts
I appreciate the reply. It's very straightforward and easy to understand; I'd just never seen it done like that (always before I'd seen power to the switch first). I would have thought with this arrangement you'd still do B-B and W-W, as it would still function the same, but it's good to know this is common in case I see it again.

With the fan, I'm probably going to just disconnect the switch entirely, as I really see no reason to need it. In fact this switch is now behind a bookcase and it takes a stick to turn it on! LOL (it used to be a dining room; now is my computer room/office).

What are your feelings about the strength of a plastic box's threads? It would be easier to use the existing box and put lag bolts into a new 2x4; but would the threads be strong enough?


03:25PM | 05/02/07
Member Since: 04/25/05
1915 lifetime posts
There are some Fan Rated boxes (I suspect that amount other things they have metal inserts for the threads).

But most plastic box can sag.
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