Over the years, I have done a bit of relatively simple wiring around the
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
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 ?
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.
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
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
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
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.
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.
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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