When wiring up normal 3-prong outlets, does it matter if I switch the
black and white wires on a single outlet in the run?
I've heard the polarity doesn't matter...but want to make sure I'm not
going to short it out or something else horrible.
Also, when wiring up lights, does it matter which color wire I run to
the switch? Most of the how-to articles show cutting the white
wire...does it make any difference?
It matters. And I doubt your last paragraph correctly describes those
The concern relates to safety and failure modes. Either way will appear
to work. But the wrong way will be unsafe and violate code.
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form email@example.com.
Yes it matters that the white wire goes to the larger hole side of the
outlet and the black wire goes to the smaller hole side of the outlet.
Then when things are plugged in, they are safer if the outlet is wired
properly. For example a table lamp with one prong larger than the other. You
can only plug it in one way. The larger prong (white wire) goes to the
"ring" part of the light bulb. The smaller prong (black - hot) goes to the
switch and then to the contact down in the center of the socket.
You can get electrocuted if you touch the black hot wire. It is safer it
this is the wire going to the contact in the bottom of the light socket. It
is easy to accidentally touch the metal ring of a light bulb when changing a
light bulb. Best if it is connected to the white (neutral) wire and NOT to
the black hot wire!
So wire your outlets properly and wire lamps and appliances properly. Get a
book on wiring or call an electrician. These things are done to protect YOUR
life and the lives of YOUR family.
The black wire (which can be any color, actually, except white) is the
The white or 'natural gray'-insulated wire is the 'neutral'. Think of
as a permanently pressurized 'pipe', and the neutral as a 'drainpipe'
only carries electricity when the 'faucet' (switch, appliance, etc) is
Now, lights and other plug-in appliances are designed so that the 'hot'
is less accessible than the 'neutral'. Ex.: the bulb 'shell' is
to the white 'neutral', and the contact at the socket bottom is 'hot'.
This ensures that if somebody is removing a dead bulb with the light
still on (for instance) and brushes against the shell, they are
to get a shock (unless something else is wrong with the wiring). If
hot and neutral are reversed, this shell would be connected to the
'supply pipe' and not the 'drain pipe', and the user would be shocked.
(Note that it is still possible to get shocked by a neutral, but it is
Moral of the story: Safety dictates that hot and neutral must be
connected. Follow the manufacturer's directions. If for some reason
easier to do it the wrong way, that's too bad. Do the job right.
Now for switches. Switches must always control the 'hot' side of a
cutting off the 'supply pipe'. That way, with the switch off, the only
connections (if the light is properly wired) are to the 'drainpipe',
side. When a switch is in the neutral it will still stop current from
the light will turn on and off with no problems. However, even with
switch off, all terminals and wires in the lamp will be 'hot', part of
pressurized pipe of electricity, waiting for somebody to provide a path
Moral of the story: Switches must be in the 'hot' wire, never the
This is a common problem in old houses, where some damfool cut off
and reconnected an old K&T run (where the conductors may be hard
to tell apart) without bothering to check which was which.
There is one situation where you may find a white wire on a switch.
Power may go to a lamp or other switched outlet,then out to a switch
and back to the outlet on the two conductors of one cable. This is
known as a 'switch loop'. If you find a switch with only one
2-conductor cable coming into its box, and something goes on and
off when you flip it, you are definitely dealing with a switch loop.
a switch loop, all wires are considered 'hot'. If using cable, code
the white wire to be used as part of a switch loop, but it is not a
neutral, is not connected to any other neutrals, and must be
reidentified some other color where the wire is exposed inside the
Story time. My brother found an (overstuffed) j-box with a
receptacle in it, in a basement. Removing the receptacle, he proceeded
to wirenut all whites and all blacks together, then turned on the
All well. Then he flipped the basement light switch. ZAP. One of
white wires was actually part of a hacked switch loop. He had
created a bolted short. Unfortunately, the circuit was also part of an
absurd multiwire circuit (which split 6' from the service panel) which
equally hacked, with overstuffed boxes, insecure connections, and
puny wire nuts, and one leg of this circuit was overfused. Both
tripped. My brother, being sensible, switched off the offending
and turned the breakers back on. Well, some lights went poof, and
the phone, and some other electronic gadgets, now acted really
funny in a not-working way. Apparently the neutral of the multiwire
circuit had failed somewhere. Rather distressed by this, he shut off
both breakers (I told you he had sense) and we later straightened
everything out. This involved replacing one 4" octagon box with two
4S boxes and eliminating such idiocies as the elusive "switch threep"
- one wire to the switch, one wire from the switch to each of two
using two pieces of 12-2 with one wire unused. Ugh.
Moral of the story: learn what you are doing before you do it. There
good books out there. Get a permit and get your work inspected.
It costs less than burning the place down. Finally, don't use USENET
as your sole source, and definitely don't use the home center.
House wiring is not as simple as some think.
On 20 Nov 2006 09:15:50 -0800, " firstname.lastname@example.org"
Yes, it does make a difference.
As another poster mentioned, switch on the wrong wire allows switched
devices, such as lamp sockets, to be hot - you get shocked if you touch
such items and ground.
As for outlets - those have designated hot and neutral terminals that
should not be reversed. Many appliances have polarized plugs. If a lamp
has hot and neutral reversed, then the exposed part of the base of a
partially screwed-in lightbulb will be hot - even if the lamp's switch is
Also keep in mind that in some fluorescent lamps, reversing hot and
neutral can adversely affect the electric field distribution within a bulb
that is trying to start, and that may impair starting.
- Don Klipstein ( email@example.com)
To be safe & meet code, all 120V outlets will be wired with
the neutral (white) connected to the neutral terminal on the outlet,
indicated by the silver screw; hot (almost always black, sometimes
red) connects to the brass colored screw; and ground, which is
bare or green insulated, connects to the green grounding screw on
the outlet. (or to the grounding screw of the outlet box, if box &
outlet are designed for this; usually the case when metal boxes are
If by "switch the black and white wires" you mean connect
them opposite to above description, then doing so will create a
potentially unsafe condition. OTOH if you mean to install a switch to
control that outlet, then only the black or hot wire should be
switched. The neutral or white should always connect directly to the
outlet. In either case, there is only one correct way.
The term "polarity" has to do with positive & negative, and is
important in direct current systems, e.g. automotive. It really has no
bearing on a discussion of alternating current house wiring.
As far as connecting a light to a switch, there are a couple different
ways the wiring can be routed, that will make a difference as to which
color wire should go where; However, in all cases, the current
carrying neutral will connect to the neutral of the light fixture and
is never switched.
Why not get a good DIY book on house wiring? There are several that
do a good job of explaining both safe wiring and safe work practices.
Black and Decker sells a good one.
For every complicated, difficult problem, there is a simple, easy
solution that does not work.
OP doesn't necessarily have to hire an electrician, but does need
more knowledge before attempting to DIY this job
Electricians aren't born with their knowledge. They have to learn it.
There's no reason a person of ordinary intelligence cannot learn, in a
reasonable length of time, how to safely perform simple, basic tasks
like wiring an outlet, switch, or light fixture.
Make it as simple as possible, but no simpler.
Larry Wasserman - Baltimore Maryland - firstname.lastname@example.org
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