Wiring question; four in, two out

When we had the trailer and passageway torn down, they cut the wires that went to a flood light at the front of the house. I’m going to put a new two-socket floodlight over the new, now-exterior, door. The first thing I noticed is that there are two holes about four inches apart coming out of the wall. The next thing I noticed is that each hole has a black and a white wire coming out of it. The third thing is that the white wire from one pair is connected to the black wire of the other pair. The other black and white wires continue toward where the floodlight was. In other words: black[sup]1[/sup] to free end, black[sup]2[/sup] to white[sup]2[/sup], white[sup]1[/sup] to free end.

Why would whoever did this do it that way? Why not just have one pair of wires?

Is there a switch?

That is typical of switch loop wiring. When you wire it that way, you are supposed to put black tape over the white wire so that you can tell it’s actually a hot wire, but a lot of people don’t wrap tape over the wire.

A picture is worth a thousand words:
(Note that the pic has the tape around the switched white wire at either end)


Why not have the power wires go to the switch, and then have wires going from the switch to the fixture?

Takes, or can take, more wire. Depending on where the power is in relation to the light.

It can be done either way.

If you have the unswitched hot and neutral available in the box, you can run another wire off of that to an additional light which will then have its own switch loop. That saves on running the wire for the second light all the way back to the breaker box.

So it takes less wire.

AFAIK, the switch only powered the flood light. On the other hand, whoever did it probably did it in the mid-'70s. Who knows what might have been powered? I’ll leave the wires as they are when I install a new flood light (over the door instead of at the corner of the house), except for making the two wires going to the fixture shorter. I wish the installer had used a single hole. Two holes are probably going to be awkward with the waterproof electrical box that makes up the base of the fixture.

Note that that type of switch loop won’t meet recent NECs. Here’s a cite: http://www.renovation-headquarters.com/switch-loop.html