Common Wiring Mistakes

From: The Grassroots Newsletter - April 2007

Editor's Note:

This month's article is about how to recognize and correct wiring mistakes that can endanger a home. Electrical projects are best left to the experts. Just ask my step-brother. He works in a coal mine and I suppose he thought this gave him the expertise to install a microwave over his range. Long story short...his house burned to the ground 3 weeks ago. For all of the experts out there, the tips listed below may well be worth pointing out to a customer when you are doing the project hired to do.

Common Wiring Mistakes

First and foremost, always turn off power at the main panel when doing any electrical work.

Never connect wires outside of an electrical box, as these boxes protect the connections from accidental damage and they contain any sparks and heat from loose connections or short circuits. If you find a connection without a box (porch lights, for instance), install one and reconnect the wires inside it.

Short wires most likely cause bad connections. Leave enough wire for at least 3 inches to protrude from the electrical box. If you find wires that have been cut too short, you can add extensions by using wire connectors. P ush in wire connectors are great to use in tight spaces and can be found in hardware stores or do-it-yourself home centers.

Cables must be protected between framing members, since it is especially vulnerable when run over or under wall or ceiling framing. Protect the exposed plastic sheathed cable by screwing a 1 1/2 inch or 2 x 2 inch thick board alongside the cable. There is no need to staple the cable to the board.

Loose switches and outlets are dangerous. They can move causing the wires to become loose from the terminals and loose wires have been known to arc or overheat. An easy fix would be shimming under the screws, special electrical spacers that are placed over the screws before screwing into the wall, or a coil of wire wrapped around the screws.

Here's the one my step-brother should have heeded... never replace a two-prong outlet with a three-prong outlet without making sure there is a ground wire available. An inexpensive tester purchased at any hardware store will tell if the outlet is grounded. By the same token, if you find a three-slot outlet in an ungrounded box, replace it with a two-slot outlet.

All electrical boxes must be flush to the wall surface if the surface is of a combustible material. Never recess an electrical box behind combustible surfaces. If you find this to be the case, install a metal or plastic box extender. If you use a metal box extension on a plastic box, make sure you connect the metal extension to the ground wire in the box using a grounding clip and a short piece of wire.

Never install a cable without a clamp. Single plastic boxes don't require internal cable clamps, but you must staple the cable within 8 inches of the box. For larger plastic boxes, a clamp must be used and the cable must be stapled within 12 inches of the box. Approved cable clamps must be used to connect cables to metal boxes, making sure the sheathing on the cable is trapped under the clamp and 1/4 inch of sheathing is visible inside the box.

Use the correct size box. According to the National Electrical Code, to determine the minimum box size required, add up all the items in the box (each hot and neutral wire entering the box, all ground wires combined, all cable clamps combined, and each device - switch or outlets, but not light fixtures). Multiply the total by 2 for 14-gauge wire and 2.25 for 12-gauge wire to get the minimum box size required in cubic inches. You must choose a box with at least this much volume. Plastic boxes have the volume stamped on it. For metal boxes, measure the height, width and depth of the interior and multiply to find the volume.

If a hot wire is connected to the neutral terminal of an outlet, the outlet will still work, but won't work safely and could cause a lethal shock. White wires are connected to the neutral terminal of outlets. The terminal is always marked, usually by a silver or light colored screw. Black (hot) wires are connected to the other terminal. A green or bare copper wire is the ground and is connected to the green grounding screw or to a ground wire or grounded box.

The shock protection will be lost in GFCI (ground fault circuit interrupter) if the line and load connections are mixed. There are two pairs of terminals. One pair is labeled 'line' and it is for incoming power for the GFCI outlet itself. The other set is labeled 'load' and provides protection for downstream outlets.

Darren
www.contractorexam.com