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Revisiting the Subject of Knob & Tube Wiring

March 10, 2020

Knob and Tube Wiring a Potential Hazard

Knob and tube wiring that was installed and used correctly and remains in exceptional condition is not dangerous. Nevertheless, given the fact that these wiring systems haven’t been installed in homes since the 1940’s, knob and tube wiring present in homes today are certainly aging.

Stretching and sagging is a common problem, which can lead to unsafe contact between the wires. Insulation can weaken, and breakdown to expose the copper wiring. These systems lack a grounding conductor, which are standard in today’s wiring systems to reduce risk of electrocution and electrical fires. Furthermore, when these systems were installed, most of today’s appliances didn't exist, so they were designed for much lighter electrical loads than is standard today. As a result of the increased demand, knob and tube systems are often overloaded, which cause wires to overheat and become brittle, creating hidden hazards inside the walls.

Deficient modifications are a very common problem with knob and tube wiring as well, as amateur upgrades that have often been made over the years to oblige increasing electrical needs. One common issue found in these systems is inadequately done, unsafe splices that were meant to expand the system. Fuses are another problem area, as many homeowners, in order to reduce the frequency of blown fuses, replaced properly sized fuses with ones with higher resistances. This does prevent the fuses from blowing as often, but only by allowing circuits to be overloaded, which causes heat damage to the wiring.

Home insulation and knob and tube wiring can be a dangerous combination, since this form of wiring relies upon open space to disperse heat. When insulation is placed around these wires, heat can’t escape as it should, which can cause wires to overheat or break, becoming a fire hazard. The National Electric Code (NEC) states that knob and tube wiring should not be in hollow spaces of walls, ceilings and attics that are insulated with loose, rolled or foam materials that envelope the conductors.

Home Insurance Issues

If your home has knob and tube wiring that’s still in use, you may find that home insurance companies are hesitant to sell you a policy. Some insurance companies refuse to insure homes with this type of wiring altogether, while others may insure you after your system has been inspected and declared safe by a qualified electrician.

The bottom line is that knob and tube wiring is very likely to create a safety hazard in your home. Upgrading the system is an investment, but one that will pay off in safety, peace of mind, and a more functional and efficient electrical system. For more information on knob and tube wiring please contact McCurdy Electrical Services, Inc. at 781-595-7074.


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