Power failures are usually neighborhood or even regional events. But problems of electrical safety and capacity also surface in household wiring, particularly if the house is more than 20 years old. (Nationwide there are about 70 million of them, according to the Census Bureau.) That may seem too young to have trouble in basic systems -- and it is for most of the house. But many upgrades to the National Electrical Code (NEC) cover fundamentally new equipment and also account for dramatic increases in residential electrical use.
In homes that don't measure up, the most common problems, says the Copper Development Association, are worn wiring, inadequate circuits and overuse of extension cords, covered last week. This week, we'll look into less obvious trouble spots that a licensed electrician may have to deal with to make your house safe.
High attic temperatures. To permit a free-flowing supply of electricity, wiring has to be large enough to carry the load. If it isn't, the power, in a way, is forced through the wire, which offers more resistance. That resistance, in turn, produces heat, which can lead to serious problems, including fires.
But in attics, even wiring that's adequate for the load can overheat because the space becomes so hot in the summer. Overheating can also be a problem if attic wires are bundled closely together -- for instance, to pass through holes in framing.
Separating wires will help -- an issue covered by the latest additions to the NEC. But the best safeguard against overheating in attic wiring is to use wires with larger diameters that offer less resistance. For example, if a circuit calls for 14-gauge, use 12-gauge. Bear in mind that in the American Wire Gauge system, the lower the number, the larger the wire diameter and capacity.
Aluminum wiring connections. Due to the shortage and rising cost of copper in the 1960s and 1970s, many homes were wired with aluminum. The Consumer Product Safety Commission (CPSC) estimates that two million homes were built with this alternative between 1965 and 1974. (It's marked "AL" or "Aluminum" every few feet along the cable.) It should have been clear that aluminum wiring of that era was going to cause trouble. It was more brittle than copper, more likely to break during handling and more likely to corrode. In contact with moisture, oxidation would cause deposits to build up, creating resistance and heat.
Although it seemed to work well at first, problems developed at outlets and switches where cable insulation was stripped back and aluminum wires joined copper connectors. Due to a combination of problems generally known as "cold creep," the dissimilar metals tended to work loose, exposing live wires that caused electrical shocks and started house fires.
Joining short lengths of copper wire to the aluminum near outlets and switches (called pigtailing) is one solution, and far less expensive than the other -- rewiring the entire house.
The CPSC says that splicing with twist-on connectors or changing to aluminum-compatible outlets and switches are inadequate solutions. The agency recommends only one in-wall fix: pigtailing with a thermoplastic seal at each splice, called the Copalum crimp connector system, made by Tyco Electronics.
Fuses and circuit breakers. These built-in safety devices shut down parts of the system when there's a problem -- unless there's a problem in the devices themselves.
Like any mechanical device, circuit breakers can wear out and break. But if one of them keeps tripping, the problem is almost always in the circuit wiring -- and needs immediate attention.
Fuses (a clear indicator of an aging system) also offer good protection. The problem is that homeowners sometimes swap out fuses with the wrong ratings. (No one is thinking of defeating the system by inserting a penny, right?) When fuses blow repeatedly (as when breakers keep tripping), there's a problem in the circuit that needs to be fixed. Replacing a blown 15-amp fuse with a new 30-amp fuse may stop the blown-fuse problem. But excess power will be able to flow through circuit wiring that isn't designed to carry the load.
GFCI protection. Ground fault circuit interrupters are outlets combined with circuit breakers. They provide superior shock protection by comparing current in the outlet's hot supply wire and neutral return wire. If there's a difference, electricity could be passing through your body, and the built-in breaker instantly shuts off the power.
They first appeared in the NEC in 1968 to protect swimming pool lighting.
Since then, code upgrades have expanded GFCI requirements to many locations inside and outside the house. Generally, you should find them near water and moisture sources where shock hazards are greatest, particularly in kitchens and baths as well as outside. If you don't find them, have them installed where required.
You may also want to check into the latest evolution in electrical safety devices -- an arc fault circuit interrupter, or AFCI. Unlike GFCIs that guard against overloads or short circuits, these devices detect electrical arcing across breaks in wires. They are particularly valuable in rooms where deteriorating lamp cords, for instance, may arc and create sparks that trigger fires.