January 13, 2005
FOR IMMEDIATE RELEASE
ORLANDO, FL— When you're up in an attic on a sunny summer day, you know the meaning of hot. If there's a dark-color roof on the house, the heat buildup can be especially unbearable. Well, pity that home's electrical wiring - it has to perform in this superheated environment day after day.
The heat doesn't affect the copper conductors in the wiring. They can handle far higher temperatures than those found in attics. The problem is the plastic insulation and jacketing that surround the wires. These are usually rated to withstand up to 194 degrees F, but temperatures that approach this limit are not recommended.
Two factors combine to heat up the wire, according to Bill Black, vice president of Wire and Cable at the Copper Development Association (CDA).
The first factor is the heat in the surrounding, or ambient, air in the attic. Recent CDA research found that ambient temperatures in attics can easily rise 30 to 50 degrees higher than the outdoor temperature (the temperatures the weatherman quotes are measured in the shade).
As if that weren't enough, consider the second factor: the electrical current running through the wires heats them up even more. CDA research has shown that the cumulative effect of ambient heat and current on attic wiring installed in the open air can result in temperatures that come perilously close to the 194-degree limit. If the wires are buried in attic insulation, pass over light fixtures or, worst of all, are arranged in tight bundles, they get even hotter than if they're out in the open.
One way to alleviate the heat is to install larger diameter wires - for example, use 12 AWG instead of 14 AWG, or 10 AWG instead of 12 AWG (larger wires have smaller American Wire Gauge numbers). Because larger wires offer less resistance to electrical current, they permit more current flow while staying cooler.
Another, perhaps more practical, solution is to add more circuits. That divides the electrical current among more wires instead of just a few overtaxed circuits. Additional circuits and circuit breakers also provide an increased safety margin. If you prefer this solution, you'll have to run some new lengths of wire, and it's always a good idea to use larger wires than those in place now.
Electrical usage per home has more than quadrupled in this country since the 1950s. As a result, the wiring in many older houses, particularly those that have not been upgraded over the years, may be insufficient and vulnerable to dangerous overheating. Newer homes that are wired to minimize cost may be susceptible to overloading, too.
Some of these findings have already resulted in new wiring provisions in the 2005 National Electrical Code. Builders and remodelers are urged to consult with their electricians to ensure occupant safety and avoid future liability.
For more information on residential electrical wiring, visit our Building Wire section.