Updated: Dec 31, 2020
Knob and tube wiring is an antiquated wiring method that was used in homes during the late 1800s until the 1950s. During its time it was state of the art wiring but by todays standards and code regulations it is considered out of date and unsafe. Even though it hasn’t been installed in structures in the last seventy years, there are still quite a few homes with this mode of wiring in use. While electrical upgrades generally replace the knob and tube (K&T) wiring, oftentimes it remains intact in areas with limited access or where updates have not been done. In many cases the knob and tube wiring is overall safe but it can pose issues with getting a homeowners policy renewed or activated. Below are a few facts about knob and tube wiring.
How Knob and Tube Wiring Is Designed
Knob and tube wiring is made of three components: a white tube, or cylinder made of ceramic or porcelain and white and black wires that are sheathed in rubber and sometimes cotton or another cloth. The wires run along joists in the home and are capped off by the ceramic tube to hold them securely in place.
#1 It Has No Ground Wire: Knob and tube wiring has no ground wired bundled in with the black and white wires, so electrical load is limited. This also means an increased risk of shock or fire.
#2 Mixing K&T and Building Insulation Poses Hazards: The design of knob and tube wiring with its ceramic cylinder holding the ends and the wires being encased in rubber, it needs good air circulation, thus placing insulation around the wiring could be a fire hazard.
#3 Low Current Capacity: During the era of K&T wiring, homes did not require the same electrical load as do homes of today, so this can easily cause circuits to overheat or short out.
#4 Less Resistant To Damage: The limitations of the K&T wiring design are less resistant to moisture and heat. Over the course of time the wiring and rubber can dry out and crack; and a professional should correct this along with any frayed wiring immediately.
Knob and tube wiring is easy to splice into to connect with modern wiring, and this is where problems can arise, if done by amateurs. This and the condition of the wiring will often be a determining factor as to whether or not an insurance company will provide home coverage. Most insurance companies will however, accept a letter from a certified home inspector if the K&T is found in safe condition.
As a homeowner, there is no urgency to replace knob and tube wiring that is in good condition. However, you should have it inspected regularly to ensure it does not become a safety hazard.
If you are a prospective home buyer looking at older homes, be sure to get a home inspection prior to finalizing the purchase. It will give you peace of mind knowing that you are fully aware of what you are signing up for. Please contact us today to schedule your inspection.
The Author Schenectady NY Home Inspections LLC is a locally owned and family operated Home Inspection Company. Schenectady NY Home Inspections is located in Schenectady NY and has performed over 6500 Inspections Book online