1) Leave enough wire at the outlet boxes. Short wires make it hard to install or replace the switch or receptacle, should the need arise. You must leave at least six inches of wire extending outside of the outlet box.
2) Properly install the cables in the outlet box. The cable sheath must be inside the box at least 1/4" to 1/2". You should not see the individual conductors outside of the box where the cable enters. If the box has cable clamps, make sure they are snug to prevent the cable from coming out of the box.
3) Many times cable is installed where it can be damaged. Anytime NM-B or UF cable is run outside of the framing members, it shall be protected by some type of conduit, either flexible, PVC, or rigid conduit.
4) If UF is installed feeding a pole light or utility building, it shall be protected by either a metallic or PVC conduit to keep it from being damaged by gardening tools, pets, pests and etc. Schedule 80 PVC conduit must be used to protect the UF down at least 18" into the ground and up to 48" when it emerges from the ground or a slab.
5) Use a proper connector when inserting the cable into a metal box, light fixture, bath fan or panel board. A proper cable connector must be used to keep the sharp edges of the metal from damaging the cable sheath and causing a short circuit or possibly a fire.
6) The NM-B should be stapled within eight inches of the box and at least every four feet thereafter. Be careful when stapling that you do not damage the cable with the hammer. Do not drive the staple so tight as to damage the cable. Drive the staple so that it is just snug enough to secure the cable. Be sure to staple cables flat on the framing member (see diagram). Be sure to run the NM-B along and parallel to building members in a neat appearing manner. Do not travel diagonally across the attic or under the floor. Stay at least 6 feet away from any access. If you have permanent access to an attic or a crawl space more than 4 feet high, cable shall not be run on the face of the joist.
7) Be sure to keep the NM-B cable at least 1 1/4" from the finished edges of your framing member. This is to keep the NM-B from being damaged by nails that miss the framing member while the wall or ceiling finish is installed.
8) Drilled holes in framing members shall be a minimum of 1 1/4 inches from either face of the framing member, or shall be protected by using a steel plate 1/16 of an inch thick or a listed, approved steel plate of lesser than 1/16 inch of appropriate length.
9) Use the proper cable for the job. It is a common mistake using NM-B cable for underground or direct burial use. I know it looks like it will withstand burial because it has a plastic-like coating. But, it will not last long especially if the ground is damp. You must use UF cable.
10) Homeowners often do not use proper replacement outlet. Always replace a GFCI receptacle with another GFCI receptacle ONLY. It was installed there for a purpose. It could save a life, maybe yours, or a loved one.
11) NEVER replace a two-wire receptacle with a three-wire receptacle. If you own an older home with ungrounded two slot receptacles, you cannot replace a two-wire receptacle with a three wire-grounding receptacle unless you run a ground wire and attach it to the grounding electrode. There is an exception to this; you may replace a two-wire receptacle with a GFCI receptacle and mark all of the outlets replaced as no ground available.
12) Do not replace light fixtures in older homes without a grounding conductor. Replacement of light fixtures require grounding if a metal fixture is installed, or install GFCI protection on the circuit. Non metallic fixtures may be replaced without grounding.
13) It is a common mistake to install ceiling fans without proper support. Be sure that if you are hanging a ceiling fan you have installed a listed ceiling fan box correctly per the manufacturer's instructions before mounting the ceiling fan.
14) Homeowners get shocked by not turning off power or checking if a circuit is live. Buy a simple voltage detector. Check your voltage tester on a known live circuit to be sure it is working properly BEFORE USING.
15) Remember the self help books are not always correct or current. The person who is giving you advice may not know as much as you or maybe only a little more than you about wiring. Most often the advice you get is worth just what you paid for it; as a matter of fact, it most often costs you a lot of money to do a project over to meet the National Electrical Code.
DO YOU REALLY WANT TO DO YOUR OWN ELECTRICAL WORK?
Nothing else in your home will operate properly if it is installed incorrectly. Just because your ceiling fan or light operates does not mean it is safe. It may take years but eventually it could fail, possibly causing a fire, major damage, or death.
Painting, roofing, floor covering, sheetrock, trim work, landscaping and a host of other projects can be safely performed by the homeowner.