Switch Wiring: One NM Lead (white re-labeled), Or Two NM Runs ?

[Robert11]

Hello:

Over the years, I have done a bit of relatively simple wiring around the house.

Have just finished reading the book by H. Richter, Wiring Simplified, 40th ed. with great interest. A very handy little volume.

Have the following question for those of you who might be doing this stuff for a living, please:

Whenever I have wired a new wall switch, I have always brought a piece of NM wire from the source to the switch, the black going to one terminal. Then I ran a second piece of NM with the black from the other switch terminal to the new light fixture, along with its white lead. (the whites would also be tied together for the two pieces of NM at the switch box).

I see in the book (p 110) where it is apparently permissible to just use a single piece of NM to the switch, with the white being re-marked black. This NM would then effectively be placed in series with the normal black wire from the source and to the fixture. (the white from the source also going to the light fixture).

The approach i have been using which I described in the first paragraph isn't even described in the book.

So, other than the first approach using twice the amount of NM, is there any advantage one way or the other ?

What do you folks do in a simple situation like this ? Why ?

Thanks, Bob

[Andy Hill]

If the drywall isn't up, I'll usually do the former. Gives me more leeway for future mods.

If it's a retrofit, I prefer to fish as little as possible, so I'll just do the switchleg approach.

[bill a]

both ways are fine. which method uses less wire depends on the relative positions of feed-switch-load. as the other poster said, when finish walls are up, you do them any way you can. bill

[Beeper]

[nospamgoingjag]

If the source starts at the switch, then it's not an issue.

Power to switch, end of first NM run, wire from switch to light or switched outlet, second NM run. Only one NM used.

Now if the source "originates" or passes through where the light is to begin with, then you have the situation you describe. You put the source white to one side of the light, then take the white you just cut and put it on the other side of the light label it black. That NM continues to the switch with the black going to one side, and the white to the other side, and labeled white.

snip

[xrongor]

I have an average-size 3 bedroom, 2 bath house that needs a new roof. The old one's fine, it's just getting a little thin in places where it was hit by hailstones, and the gritty stuff on the shingles seems to be coming off more than it used to. The roof is 9 years old. We're in central Texas, near Austin. It's just a standard, asphalt composite shingle roof.

I can replace this roof myself - I've done this before - but one question. Is there some method or device I can use to get those packages of shingles up onto the roof? These things are HEAVY. I picked up one at Home Depot, and one package must weigh 80+ pounds. I can't imagine hauling a roof-full of them up a ladder, one at a time.

Thanks, R.M.

[xrongor]

lol, now theres a fake me running around.

randy

[Chris Lewis]

According to Robert11 :

Either approach is perfectly fine.

People generally tend to use the "single NM" (it's called "switch leg") if it's more convenient for unswitched power to go into the fixture first.

Many books appear to prefer the switch leg approach, but I've never been quite sure why. It may be because typical wiring practises tend to mean that they use fixtures as junction/distribution points, and it probably tends to use less wire - perhaps because it's usually easier to route wire through ceilings than dodge around walls.

I happen to prefer to use switch boxes as the junction/distribution points, and don't mind a little extra work.

In some cases, switch leg is more convenient. Ie: if you change over a switch-legged ceiling light to a fan/light combo, since you have both switched (say for the light) and unswitched hot (say for the fan, use the pull cord) in the box, you don't have to replace the switchleg with 3 wire in order to have the fan on, and light off.

I personally don't like switch leg, because it means that boxes are live even when switched off (not that you should rely on that anyway!), and that means that white wires carry hot. Since I plan my systems with the hot going to the switch first, it doesn't really use much more NM if at all.

I install 3-wire if I'm planning on using a ceiling fan.

[xrongor]

What ever makes you thing that? I think this group is just under an April Fool attack.... If you look closely, this whole group is total chaos today.

randy