Question: There was a house fire on our street last week. Investigators traced the cause to a short circuit in an electrical wire. Now I'm terrified that a fire can start in my home without warning.
Why didn't the person's circuit breaker trip as soon as the wire shorted? Is there a way to prevent fires caused by short circuits in electrical wiring?
Answer: Your neighbor's fire was just one of about 115 electrical fires that happen each day in the United States. They cause hundreds of millions of dollars in damage, injure thousands of people and account for hundreds of deaths each year. I can see why you're terrified.
Any firefighter will tell you that electrical fires are indiscriminate. They can strike anywhere at any time.
The electrical shorts that cause these fires produce arcs, miniature fireworks in which temperatures approach 10,000 degrees. This intense heat can rapidly ignite plastic insulation, wood, carpeting or any other combustible material in the vicinity.
Arcs happen frequently in appliance electrical cords where insulation has become brittle or cracked. Hidden wires behind walls nicked by nails or pinched by fasteners can also be sources of arcing. Loose connections where wires are attached to switches and outlets are often arc hot spots.
The traditional circuit breakers in your neighbor's house did not prevent the fire because they are not designed to sense arc faults. They protect the wire behind the walls and the switches and outlets to which the wire is connected, tripping when they sense a short that can cause a surge of electricity. They also trip when a constant massive amount of electricity passing through the circuit causes a heat buildup in the breaker. Traditional breakers are not designed to protect lightweight appliance wires and extension cords that are plugged into wall outlets.
Fire-producing arcs can occur in wiring before traditional breakers react. Electrical manufacturers, recognizing the problem, have come up with the new arc-fault circuit interrupter breaker.
These devices work and act like a traditional circuit breaker except that they are smarter. They contain filters and logic devices that enable them to sense an arc just as it is about to produce sparks and intense heat. If arcing conditions are present, the breaker trips instantaneously.
Do not confuse these devices with the personnel protection ground fault circuit interrupters that have been around for more than 30 years. These do not have the capability to sense arcs.
The new arc-fault circuit breakers are identified in section 210-12 of the 1999 edition of the National Electric Code. Beginning Jan. 1, 2002, they will be required to protect branch circuits that serve residential bedrooms, where many electrical arc fires start.
Vermont has taken a more aggressive stance by requiring that these breakers be used in all circuits that feed residential living areas. Its regulation goes into effect Jan. 1, 2001.
Arc-fault breakers are now available throughout the country. They are the same size as traditional circuit breakers and cost about $25 each. An electrician can install one in a matter of minutes.
Tim Carter is a licensed contractor. Got a question for him? Call toll free from 10 a.m. to noon today at (888) 737-1450 on his radio call-in show (not broadcast in the Tampa Bay area).