[PLUG-TALK] electrical wiring question

Denis Heidtmann denis.heidtmann at gmail.com
Fri May 27 19:06:11 UTC 2016


On Fri, May 27, 2016 at 8:41 AM, John Jason Jordan <johnxj at comcast.net>
wrote:

> On Fri, 27 May 2016 08:03:46 -0700
> Denis Heidtmann <denis.heidtmann at gmail.com> dijo:
>
> >Is  there any legitimate reason to connect a black and white wire
> >together?  I have been trying to conjure some historical reason for
> >this wiring, but cannot.  In hindsight I desperately wish I had spent
> >some time studying the situation.
>
> This happens all the time, especially in switches, and is perfectly
> acceptable. However, electricians normally carry rolls of tape in
> common colors (black, white, red) because it is considered good
> practice to use tape to 'change the color' of a wire inside the box
> just before it connects to the appliance.
>
> The problem is that household wire comes with a black, a white, and a
> bare (earth ground) wire. (If three-conductor wire, the extra hot wire
> is red.) When wiring a switch the black and white wires travel to the
> light, and they are both hot wires, so one should wrap a bit of black
> tape over the white wire to signal to future electricians 'this wire is
> white, but it's hot.' Having said that, I think the convention of using
> tape to change the color of a wire is recent, because I constantly find
> situations in old houses where it was not done.
>
> I should add that it is good practice (although not required) to have
> power in every box, including switch boxes. I always do so because then
> I can later (if desired) swap out the switch for a switch+outlet
> appliance. That might explain the wire nuts that you saw in the box.


I still do not get it.

If the power is in the switch box, then I see the correct wiring to be a
black wire to each of the switch terminals, one from the power feed and one
to the light.  The white from the power feed is connected via wire nut to
the white wire to the light.  This means the switch is in the power leg, so
that when the switch is off there is no power at the light.  If the power
is to go elsewhere from the switch box it can be connected directly to the
power feed, white-to-white and black-to-black.

If the power feed is in  the light, then the switch will have one white and
one black.  The existence of more white wires in the box seems to eliminate
this option.  I did not see any red wire in the box.
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