Many homes built prior to 1950 have a type of electrical wiring known as "knob and tube." This wiring consists of porcelain insulating tubes that contain wires — whereas modern wiring is usually run through plastic or PVC tubes. The porcelain tubes pass through beams, rafters, and walls, and porcelain knobs are used to carry the wire around corners.

At times, homeowners with this older wiring can find it difficult to obtain insurance on such homes because some insurance companies are skittish about taking on a house they perceive as risky.

Many insurers require an inspection to show that the coating on the wiring is in good condition. If it is, they may write you a policy. If the coating is cracked or deteriorating, or if a determination can't be made, the insurer may ask the homeowner to hire a qualified electrician for further evaluation and/or repairs.

Because older houses often have a lower capacity in their wiring systems, homeowners should make sure they don't have too many electrical gadgets plugged in, such as computers, stereos, and so forth. An electrical overload could easily result in a fire.

Knob and tube wiring may continue to be safe to use. Proper maintenance is the key. Where wire insulation is brittle or cracked, it should be replaced, according to Mark W. Earley, assistant vice president and chief electrical engineer for the National Fire Protection Association. Earley points out that proper maintenance is important with all electrical system components.

                    Why are insurance companies leery?

State Farm Insurance Co., for example, doesn't look favorably on houses with knob and tube wiring, says Phil Supple, a company spokesperson. Supple points to two concerns: First is the age of the house. "Because knob and tube was generally used so long ago, we are concerned about the deterioration of the electrical system as a whole," Supple explains.

Second, State Farm worries about the lack of a ground wire with this style of wiring. Knob and tube consists of two wires: a "hot" one that carries electricity to its destination and a "neutral" one that completes the circuit. Modern wiring systems reduce the chances for creating a fire hazard through the use of a grounding wire.

State Farm requires a certificate of inspection from a qualified electrician before it will insure an older home, and if the electrician gives a favorable assessment, the company may consider writing insurance for the house.

Mike Johnston, education coordinator for codes and standards for the International Association of Electrical Standards, agrees that the lack of a ground wire can be a problem, especially if the wiring is old and in shoddy shape.

Some insurers may also point to the lack of circuit breakers as a potential problem with knob and tube wiring. Having a circuit breaker can help lower the risk for a fire in a home with knob and tube wiring.

In the end, any homeowner with knob and tube wiring, or the potential buyer of such a house, should hire an electrician to give the system a complete check. If an inspection uncovers problems, you should make the necessary repairs for personal safety as well as insurance concerns.