Wiring problems and mistakes are all too common, and if left uncorrected have the potential to cause short circuits, shocks and even fires. Here's what to look for and how to fix what you find.
By the DIY experts of The Family Handyman Magazine:February 2007
wires outside of
protect the connections
contain sparks and
heat from a loose
connection or short
aren't contained in an
electrical box, install a box
and reconnect the wires
inside it. The photo
shows one way to do this for
an exterior light mounted on
Turn off the power at the main panel
when you're doing electrical work.
Wires that are cut too short make wire
connections difficult and—since you're
more likely to make poor connections—dangerous. Leave the wires long enough
to protrude at least 3 in. from the box.
If you run into short wires, there's an
easy fix. Simply add 6-in. extensions
onto the existing wires. The photo shows a type of wire connector that's
easier to install in tight spots. You'll find
these in hardware stores and home
It's easy to damage plastic-
sheathed cable that's
left exposed between
framing members. That's
why the electrical code
requires cable to be protected
in these areas.
Cable is especially vulnerable
when it's run
over or under wall or
ceiling framing, as shown
Protect exposed plastic-
sheathed cable by
nailing or screwing a
alongside the cable.
You don't have to staple
the cable to the board.
Loose switches or outlets can look bad, but worse yet, they're
dangerous. Loosely connected outlets can
move around, causing the wires to loosen
from the terminals. Loose wires can arc
and overheat, creating a potential fire
Fix loose outlets by shimming under
the screws to create a tight connection to
the box. You can buy special spacers like
we show here at home centers and hardware
stores. Other options include small
washers or a coil of wire wrapped around
If you have two-slot outlets, it's tempting to replace them with
three-slot outlets so you can plug in three-prong plugs. But don't
do this unless you're sure there's a ground available. Use a tester to
see if your outlet is grounded. A series of lights indicates whether
the outlet is wired correctly or what fault exists. These testers are
readily available at home centers and hardware stores.
If you discover a three-slot outlet in an ungrounded box, the easiest
fix is to simply replace it with a two-slot outlet as shown.
Electrical boxes must be
flush to the wall surface if
the wall surface is a combustible
recessed behind combustible
materials like wood present
a fire hazard because the
wood is left exposed to
potential heat and sparks.
The fix is simply to install
a metal or plastic box extension.
If you use a metal box
extension on a plastic box,
connect the metal extension
to the ground wire in the
box using a grounding clip
and a short piece of wire.
Cable that's not secured can strain
the connections. In metal boxes,
the sharp edges can cut the insulation
on the wires. Single plastic
boxes do not require internal
cable clamps, but the cable must
be stapled within 8 in. of the box.
Larger plastic boxes are required to
have built-in cable clamps and the
cable must be stapled within 12 in. of the
box. Cables must be connected to metal
boxes with an approved cable clamp.
Make sure the
sheathing on the cable is trapped under the clamp, and that about 1/4 in.
of sheathing is visible inside the box. Some metal boxes have built-in
cable clamps. If the box you’re using doesn't include clamps, buy clamps
separately and install them when you add the cable to the box.
Too many wires stuffed into a box can cause dangerous overheating, short-circuiting
and fire. The National Electrical Code specifies minimum box sizes to reduce this
To figure the minimum box size required, add up the items in the box:
1 - for each hot wire and neutral wire entering the box
1 - for all the ground wires combined
1 - for all the cable clamps combined
2 - for each device (switch or outlet—but not light fixtures)
Multiply the total by 2.00 for 14-gauge wire and by 2.25 for 12-gauge wire to get the minimum box size required in cubic inches. Then choose a box with at least this much volume. Plastic boxes have the volume stamped inside, usually on the back. Steel box capacities are listed in the electrical code. Steel boxes won’t be labeled, so you'll have to measure the height, width and depth of the interior. Then multiply to find the volume.
Connecting the black hot wire to
the neutral terminal of an outlet
creates the potential for a lethal
shock. The trouble is that you
may not realize the mistake until
someone gets shocked, because
lights and most other plug-in
devices will still work; they just
won't work safely.
Always connect the white wire
to the neutral terminal of outlets
and light fixtures. The neutral terminal
is always marked. It's usually
identified by a silver or light-colored
screw. Connect the hot
wire to the other terminal. If
there's a green or bare copper
wire, that's the ground. Connect
the ground to the green grounding
screw or to a ground wire or
GFCI (ground fault circuit interrupter)
outlets protect you from a
lethal shock by shutting off the
power when they sense slight differences
in current. They have two
pairs of terminals. One pair, labeled
“line,” is for incoming power for the
GFCI outlet itself. The other set is
labeled “load” and provides protection
for downstream outlets. You'll
lose the shock protection if you mix
up the line and load connections.
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.
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