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knob and tube wiring on 4 point inspections and home inspections.

4 Point Inspections and Home Inspections – Understand Knob and Tube wiring in your home

Posted on Apr 15, 2015 in Four-Point Inspection, Home Inspections, Industry Updates, Insurance Information | 0 comments

Have you had knob and tube wiring come back on your 4 point inspection or home inspection?? Confused on what that is and what it means to you?? This article will explain what that wiring is and what it means to you and your home.

Knob-and-tube (K&T) wiring was an early standardized method of electrical wiring in buildings, in common use in North America from about 1880 to the 1940s. The system is considered obsolete and can be a safety hazard, although some of the fear associated with it is undeserved.  Florida licensed inspectors should always disclaim knob-and-tube wiring during their inspections.

Facts About Knob-and-Tube Wiring:Knob and Tube Wiring

•It is not inherently dangerous. The dangers from this system arise from its age, improper modifications, and situations where building insulation envelops the wires.

•It has no ground wire and thus cannot service any three-pronged appliances.

•While it is considered obsolete, there is no code that requires its complete removal.

•It is treated differently in different jurisdictions. In some areas, it must be removed at all accessible locations, while others merely require that it not be installed in new construction.

•It is not permitted in any new construction.

How Knob-and-Tube Wiring Works:

K&T wiring consists of insulated copper conductors passing through lumber framing drill-holes via protective porcelain insulating tubes. They are supported along their length by nailed-down porcelain knobs. Where wires enter a wiring device, such as a lamp or switch, or were pulled into a wall, they are protected by flexible cloth or rubber insulation called “loom.”

Problems Associated with K&T Wiring:

•Unsafe modifications are far more common with K&T wiring than they are with Romex and other modern wiring systems. Part of the reason for this is that K&T is so old that more opportunity has existed for improper modifications.

•The insulation that envelopes the wiring is a fire hazard.

•It tends to stretch and sag over time.

•It lacks a grounding conductor. Grounding conductors reduce the chance of electrical fire and damage to sensitive equipment.

•In older systems, wiring is insulated with varnish and fiber materials that are susceptible to deterioration.

Compared with modern wiring insulation, K&T wiring is less resistant to damage. K&T wiring insulated with cambric and asbestos is not rated for moisture exposure. Older systems contained insulation with additives that may oxidize copper wire. Bending the wires may cause insulation to crack and peel away.

K&T wiring is often spliced with modern wiring incorrectly by amateurs. This is perhaps due to the ease by which K&T wiring is accessed.

Building Insulation:

K&T wiring is designed to dissipate heat into free air, and insulation will disturb this process. Insulation around K&T wires will cause heat to build up, and this creates a fire hazard. The 2008 National Electrical Code (NEC) requires that this wiring system not be covered by insulation. Specifically, it states that this wiring system should not be 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.

Modifications:Knob and Tube Wiring on thermal insulation

When K&T wiring was first introduced, common household electrical appliances were limited to little more than toasters, tea kettles, coffee percolators and clothes irons. The electrical requirements of mid- to late-20th century homes could not have been foreseen during the late 18th century, a time during which electricity, to many, was seen as a passing fad. Existing K&T systems are notorious for modifications made in an attempt to match the increasing amperage loads required by televisions, refrigerators, and a plethora of other electric appliances. Many of these attempts were made by insufficiently trained handymen, rather than experienced electricians, whose work made the wiring system vulnerable to overloading.

•Many homeowners adapted to the inadequate amperage of K&T wiring by installing fuses with resistances that were too high for the wiring. The result of this modification is that the fuses would not blow as often and the wiring would suffer heat damage due to excessive amperage loads.

•It is not uncommon for inspectors to find connections wrapped with masking tape or Scotch tape instead of electrical tape.

K&T Wiring and Insurance:

Many insurance companies refuse to insure houses that have knob-and-tube wiring due to the risk of fire. Exceptions are sometimes made for houses where an electrical contractor has deemed the system to be safe. This is where many people get confused when they are trying to purchase a new home and have just discovered this from their home inspection.

 

From Knob-and-Tube Wiring – InterNACHI http://www.nachi.org/knob-and-tube.htm#ixzz30CIIfBcS

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