Common DIY wiring mistakes

If spring sends you into remodeling mode, you might want to consider consulting the experts before you migrate to the nearest Lowes or Home Depot.

DIY projects are very satisfying to complete, says John Drengenberg, Consumer Affairs Manager for UL, but there are risks when it comes to electricity.

"Mistakes can be costly — or even deadly," he said. "The first and best safety tip is to call in an expert rather than be your own electrician."

UL engineers are getting a first-hand look at DIY wiring mistakes as part of a multiyear study by the Fire Protection Research Foundation in Quincy, Mass. Begun in 2003, the FPRF's Residential Electrical System Aging Research Project studies the wiring of condemned homes in several U.S. regions to determine how electrical systems hold up over the decades.

Although it is too early in the study for researchers to identify trends, mistakes typical of DIY projects have been easy to spot, said Drengenberg. According to UL, some of the most common DIY wiring mistakes are:

• Working with a live wire -- It may seem perfectly obvious, but thousands of DIYers receive electric shock injuries each year. To avoid becoming a statistic, always turn off the circuit breaker (or remove the fuse) before working on or replacing electrical equipment. If you have a pre-1940s home, history suggests that you probably have more than one breaker box, or panel board, as electricians call them.
  
  In the '40s, many utility companies would upgrade service from 60 amps to 100 or 200 amps without charge, Drengenberg explained. The utility would install an electrical meter and a circuit breaker box. Then the homeowner would have an electrician come out to wire those circuits, and the company made its money back from the increased use in electricity.
  
  "We've done six or seven houses in Alabama," he said, "and it's common to all of them."
• Using the wrong light bulb -- Most lighting fixtures have a sticker on the socket that tells you the proper type and maximum wattage of the light bulb to use. Installing a different type of bulb, or one with higher wattage, will not only make the room brighter, but also could damage the lights and cause a fire. Heat is usually the catalyst in this case because the higher the wattage, the hotter the bulb and the hotter the wire that goes to the lighting fixture.
• Not being grounded -- For optimal safety, receptacles should be wired with the proper grounding and polarity. Generally, the three-pronged outlets signify an effective ground path in the circuit. However, homes built before the mid-1960s probably won't have a grounding path, and simply replacing the existing outlet with a three-pronged outlet won't give you one.
  
  "You see instances of this in homes with older wiring," Drengenberg said. "It's no worse than if you plug your two-pronged devise into a two-pronged outlet, but it does give the homeowner a false sense of security."
  
  Wiring with a grounding path usually has a copper grounding wire with the cable, he said. In older homes, wires are just the black and white ones. If you are uncertain about whether your home's wiring is grounded, inexpensive UL Listed outlet circuit testers are available to test the circuit for proper grounding and polarity. If your outlet is improperly grounded, call an electrician before moving forward in the project.
• Splicing, splicing, splicing -- Always make sure your wiring size and type match. Splicing wires by simply twisting them together and covering them with electrical tape is rarely a good idea. Always use UL certified wire connectors (wire nuts).  Splices should also be housed in a UL listed metallic or nonmetallic outlet box. Check local electrical codes to see which type of boxes are acceptable. 
  
  In one Alabama home excavated by researchers, someone had installed lighting switches and none were properly housed. The connections were flush against the wall-back, which could have led to a fire. A proper box would help to contain a possible electrical spark, a power surge, or hot wire.
  
  Also keep in mind that circuits protected by 15-amp fuses or breakers should be wired with No. 14 AWG copper wire minimum. For 20 amps, use No. 12 AWG minimum size copper wire. Other guidelines apply, so if you expect to do any splicing, seek advice — if not professional help — before you begin.
• Hooking new lights to old wires -- Most light fixtures are marked with instructions for supply connections, such as "Use wire rated for at least 90C," which refers to the maximum temperature — 90 degrees Celsius or about 200 degrees Fahrenheit — under which a wire's insulation can safely be used. Again, if you have an older home (pre-1984, in this case) the wiring may have a lower temperature rating than the new luminaire. This isn't something most DIYers even think to consider, Drengenberg said.
  
  "It probably won't burst into flame immediately," he said, "but it does increase the risk of a fire."
  
  To avoid that risk, check your wire rating first, and either upgrade the wiring or buy fixtures within the supply connection range.