Lack of ground wire makes knob and tube dangerous, especially with three-pronged appliances.

Old and historic homes appeal to potential owners with features like arched doorways and stained glass, but they also come with their own unique problems.

Parts of the home may not meet modern building codes, remodeling can present expensive challenges and asbestos and lead paint pose health risks.

Ancient electrical systems, such as knob-and-tube wiring, also cause headaches for homeowners.

Electricians installed knob-and-tube wiring in homes from the late 1800s to the 1940s. They used porcelain knobs to anchor the wires to studs and floor joists and insulated tubes to pass wires through walls and other obstructions. It’s easy to identify because it has separate hot and neutral wires that run parallel to each other and suspend in the air to help dissipate heat. Knob-and-tube wiring doesn’t include a ground wire, making it dangerous for appliances that require a three-prong outlet, and increasing the chance of fire.

Improper modifications to knob-and-tube wiring

Knob and tube dominated wiring systems at a time when homes carried a smaller power load. Electricians never expected it to power dishwashers, air conditioners or entertainment systems, yet it’s still found in homes today. “At this point it’s very much outdated,” says Bill Hyman, owner of highly rated William G. Hyman Electrical Contractor in Silver Spring, Md. “We’re talking about wiring that was installed when we only had light bulbs and maybe electric fans.”

Electricians say homeowners and inexperienced handymen retrofitted knob-and-tube systems over the years – often incorrectly – to power today’s appliances. “When you get into real trouble is when people have tried to retrofit into it,” says John Calhoun, owner of highly rated John Calhoun, Electrician in Indianapolis. “Every time you junction it, you compromise it.”

According to the International Association of Certified Home Inspectors, “Unsafe modifications are far more common with Knob and tube wiring than they are with Romex and other modern wiring systems.” InterNACHI advises its inspectors to disclose knob and tube in home inspection reports.

Knob and tube causes insulation and fire risk

Homeowners often add insulation to improve energy efficiency in old homes. They unknowingly bury knob-and-tube wiring with blow-in insulation, creating a serious fire hazard. Contact with insulation can cause the wiring to overheat and catch fire. “If it’s covered with insulation and it’s up in your attic, it has got to go,” Calhoun says. “Knob and tube was originally meant to run in free air.”

As of 2008, the National Electric Code prohibits knob-and-tube wiring in “hollow spaces of walls, ceilings and attics where such spaces are insulated by loose, rolled or foamed-in-place insulating material that envelops the conductors.”

Replacing knob-and-tube wiring

InterNACHI says no code mandates the complete removal of knob-and-tube wiring, but says some local codes require its removal in all accessible locations.

The National Electrical Code prohibits knob-and-tube wiring in all new construction.

Although well-functioning, unobstructed knob-and-tube wiring usually doesn’t pose imminent danger, electricians recommend removing as much as possible. “We would supplement the existing wiring system with dedicated lines for the different appliances,” Hyman says. “We abandon the existing knob and tube and install new wiring or supplemental wiring.”

Hyman suggests replacing knob and tube during a home remodeling job where wall cavities may already be exposed, to minimize the need to cut into walls.

For homeowners worried about high replacement costs, Calhoun suggests taking it one step at a time. “We can stage things,” he says. “You can say, ‘Just do the kitchen,’ or ‘Do the attic.’” He warns that knob-and-tube jobs vary widely in pricing. “It’s hard to come up with a fixed price because you never know what you’ll get into,” Calhoun says.

Article by Mike LaFollette; found on Angie's List




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