Am replacing a standard wall outlet with a new USB outlet.
The house is only 7 years old.
The existing outlet uses black, white, red and green wires but the new outlet's instructions only specify using black, white and green.
Question is what to do with the red wire? (note: is live/hot along with the black)
IMPORTANT: my answer assumes that you are in the U.S. or Canada. If you're anywhere
else, this advice probably does not apply, and could be dangerous. In particular, if you're in
the UK, stop reading right here.
If you have red, black, white, and green wires feeding a duplex receptacle, then the two
outlets in that receptacle are served by different circuits -- or, more precisely, they are
served by opposite sides of what is called a multi-wire branch circuit, also known as an
Edison circuit (Google those terms for more information).
If the receptacle you are installing has only one 120VAC outlet, you can't use it here.
You need a duplex receptacle, *AND* you need to break out the tab between the two
screws on the hot side. For illustration, see
Attach the black wire to one of the hot screws (gold-colored), and the red wire to the other
hot screw. The white wire goes to either of the silver-colored screws on the other side of the
receptacle, and the green wire to the green screw.
And of course, turn off the breaker before doing any work.
Black, white and green are common for wall outlets. Often a red wire is
also used. In these cases the red wire is also a "hot" wire and it's
switchable. With a dual wall outlet, one outlet is always on and the other
outlet is controlled by a switch.
Not sure whether you can make one of the outlets in yout USB/wall outlet
switchable. That should be covered in the direction sheet. If not tape off
the red wire and just use black white and green.
On Wednesday, July 16, 2014 10:32:34 AM UTC-4, David Martel wrote:
Agree. The way you make a typical receptacle into the split kind
is to break off a tab for that purpose between the two sections. In
the case of a USB outlet, if it's made like that, which half is wired
lived likely matters, because something has to power the USB.
Good catch. It could be damn near anything. I've certainly come across
legacy wiring no sane or licensed electrician would have done. It would
take some time and testing to be sure of exactly what the OP has.
This is a case where I would be tempted to say "finding the red wire means
you win a prize - you get to call an electrician." I'd want to see pictures
before I issued any advice.
I'd probably look to mount the USB outlet in a box without an added red
wire. (-: I think they make six way outlets that stick out from the wall a
little but have USB outlets on the side as well as multiplying the existing
outlets. Some people hate them (my wife) and some people think they're
We could be talking 240VAC perhaps not even wired correctly at the panel.
Too easy for this to go lethal. Need a better read on the OP's electrical
skills before I'd offer advice other than use a different outlet. It's
likely even photos won't be dispositive and tests will have to be run,
probably with a helper at the panel.
On 07/16/2014 08:58 AM, firstname.lastname@example.org wrote:
Green or bare is always ground.
White is "cold"
Hot wires can be pretty much any other color, I usually see black, red,
yellow, brown or blue.
If there are two separate hot leads have a close look at your present
receptacle, it's possible the (presumably) two outlets have been
separated and are fed by two different breakers.
That would be useful in a kitchen (for example) to keep a coffee maker
and a toaster on two independent circuits.
Have a look at your new outlet to see if it can be wired the same way.
On a standard receptacle, there is a little tab between the outlets than
can be broken and removed to separate them
If, as trader4 suggested, one of the outlets is hot all the time, and the other controlled by a
switch, most likely the red wire is the one that's switched -- and taping it off and not using it
probably means that there's no longer a switched outlet in that room. Code *requires* that
there be a switch controlling either a receptacle or an overhead lighting outlet.
On Wed, 16 Jul 2014 15:34:56 +0000 (UTC), Doug Miller
If it reads zero, it's a switched circuit. If it reads 240, it's a
"split" or "edison" circuit. Either way, it gets treated the same,
with the exception that if it is switched you can just wirenut the
switched lead and leave it in the box, or better yet wirenut it and
disconnect it from the switch, wirenutting it there as well.
On Wed, 16 Jul 2014 15:38:04 +0000 (UTC), Doug Miller
So then why not tape the black wire and attach the red wire to the only
receptacle? It will be switched, as required.
If something had been plugged into the always-on receptacle, it can be
moved to the switched outlet or plugged in somewhere else.
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