Common wiring mistakes to avoid

Q. I just had a new two-car garage built and I am remodeling the old one-car garage into a family room. I plan to do some of the wiring myself. What are some of the common wiring mistakes I should avoid?

A. If you have ever seen a new house or remodeling project being wired, it looks pretty simple. The electrician just drills some holes in wall studs and runs some heavy insulated wire through the holes to the various conduit boxes throughout the house.

Don't be fooled. It is much more difficult to do it properly, particularly in a remodeling project where the existing framing is retained. If you make a serious mistake, someone could get electrocuted. Minor mistakes can result in a wire overheating inside a wall. If it gets hot enough, a fire can start inside a wall cavity and spread throughout your house quickly.

The first step is to contact your local building inspectors. Check to see if you need a permit and if an unlicensed electrician is even allowed to do electrical work. If you are allowed to do the work yourself, it would still be wise to have an inspector come to check your work before the walls are closed in order to make sure it meets local codes.

Keep in mind, if you do the electrical work, you are responsible for it as long as it exists. If you sell your house 10 years from now and the new owners are injured due to your unlicensed electrical work, you may be liable.

One of the most common wiring mistakes made is drilling clearance holes too close to the edges of a stud. The edge of the hole in the stud should be no closer than 1¼ inches from the edge of the stud. This is to keep nails, driven into the stud for drywall, from reaching and piercing the insulation on the wiring. If a hole must be closer than 1¼ inches, a protective metal nail plate must cover that area of the stud edge.

Even though it saves time, don't group low-voltage, communication and line voltage (120 volt) lines through the same holes in the studs. Line voltage wires carrying standard alternating current can cause interference with communication wires, such as ones from a computer or telephone. Line voltage wires should always be separated at least six inches from other wiring within a wall.

A more serious problem is if a line voltage line shorts out to a communication or low-voltage wire. This not only can cause a fire to start, but it can destroy any equipment attached to the low-voltage wiring. I have seem the entire low-voltage control system on a furnace destroyed in this way.

Plan all your wiring before purchasing the conduit boxes so you know what size boxes to get. Even the proper-sized wiring can get warm when electric current runs through it. Switches and connections with wire nuts can get even warmer. If you group too many wires, switches, etc., into a small conduit box, it may overheat and become a hazard.

Don't ever hang anything, such as a support for a dropped ceiling or a recessed light fixture, from electrical wiring. This can stretch and weaken the insulation over time which may cause higher resistance, overheating or even a short.