If you'r home in Los Angeles California, home was built in the 1950s or before, there’s a good chance you’ve got at least partial knob and tube wiring. Knob and tube is a wiring style that was popular a century ago, and many homeowners wonder if it’s still safe, or if they need an electrical upgrade. Some homeowners don’t realize they have knob and tube wiring until they have electrical maintenance done.
What is Knob and Tube Wiring?
Knob and Tube wiring is the wiring technique that was most commonly used in United States homes from 1880 to 1940, according to the International Association of Certified Home Inspectors. Though other types of wiring began to replace knob and tube wiring in the ’40s, some electricians continued to use it through the ’70s. Many homes built in the 1950s or 1960s still have some knob and tube wiring today.
Knob and tube wiring uses porcelain knobs and tubes to conduct the wire through the building. The wire is attached to the porcelain knobs in open air spaces, and is protected by the porcelain tubes if it has to go through a solid, like a joist. Knob and tube wiring only has two wires, which means it lacks a ground wire and therefore can only lead to a two-pronged outlet.
It may sound old-fashioned now, but knob and tube wiring has several built-in security implements. When the wire was installed correctly, the wiring was run well away from nails, the neutral and hot wires were always separated by several inches, and the porcelain rarely wears out.
Typical Problems with Knob and Tube Wiring
Some experts report that knob and tube wiring is extremely dangerous, while others maintain that if it was installed correctly originally and has suffered little wear and tear over the years, it is still safe. One of the problems with knob and tube wiring is age: because the wires are exposed, natural erosion may happen, even when protected inside the walls. Similarly, insects and animals may disturb the wiring.
Even if your home has knob and tube wiring that was impeccably installed in the 1960s, today that wiring would be 56 years old. Five and a half decades is a long time, and during that time something could have damaged your wiring. Plus, insulation can’t come into contact with it. If you need to insulate your walls, knob and tube wiring is going to get in the way.
The other main problem with knob and tube wiring is switch placement. Often, the switches went on the neutral wire rather than the hot one. That means that even if you turn off your circuit, you’ve still got an active current. The lack of a ground wire means you’re not protected from surges or short circuits, either. It also means that you’ll have a harder time finding insurance, because insurance companies don’t want to cover homes that don’t have ground wires.
Having Knob and Tube Wiring Replaced
Knob and tube wiring is no longer permitted to be installed in new constructions. Some city codes require that all knob and tube wiring be removed and replaced, while others are less strict about buildings with existing knob and tube wiring. If an electrician examines your knob and tube wiring and determines that it’s safe, you may be able to get away with leaving it in your house. However, most electricians are going to recommend an upgrade. In the long run, replacing your knob and tube wiring provides you with better electrical safety.
Knob and tube wiring isn’t something you should replace yourself, no matter how skilled you think you are. Only a professional can evaluate what needs to go into a re-wiring job for the existing knob and tube wiring in your home.
If you’re wondering about the wiring in your Pinellas County house, Luminous Electric is here to help. We can inspect your current wiring, let you know if you have any knob and tube wiring, and give you an estimate for replacing it. Call us today at.
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.
InterNACHI inspectors should always disclaim knob-and-tube wiring during their inspections.
Facts About 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 don't, but inspect it for safety reasons.
It is not permitted in any new construction.
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.
Local jurisdictions may or may not adopt the NEC’s requirement. The California Electrical Code, for instance, allows insulation to be in contact with knob-and-tube wiring, provided that certain conditions are met, such as, but not limited to, the following:
A licensed electrical contractor must certify that the system is safe.
The certification must be filed with the local building department.
Accessible areas where insulation covers the wiring must be posted with a warning sign. In some areas, this sign must be in Spanish and English.
The insulation must be non-combustible and non-conductive.
Normal requirements for insulation must be met.
Modifications:
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.
Advice for those with K&T wiring:
Have the system evaluated by a qualified electrician. Only an expert can confirm that the system was installed and modified correctly.
Do not run an excessive amount of appliances in the home, as this can cause a fire.
Where the wiring is brittle or cracked, it should be replaced. Proper maintenance is crucial.
K&T wiring should not be used in kitchens, bathrooms, laundry rooms or outdoors. Wiring must be grounded in order to be used safely in these locations.
Rewiring a house can take weeks and cost thousands of dollars, but unsafe wiring can cause fires, complicate estate transactions, and make insurers skittish.
Homeowners should carefully consider their options before deciding whether to rewire their house.
The homeowner or an electrician should carefully remove any insulation that is found surrounding K&T wires.
Prospective home buyers should get an estimate of the cost of replacing K&T wiring. They can use this amount to negotiate a cheaper price for the house.
In summary, knob-and-tube wiring is likely to be a safety hazard due to improper modifications and the addition of building insulation. Inspectors need to be wary of this old system and be prepared to inform their clients about its potential dangers.