Picking the right house to purchase is always a stressful situation. Top that off with finding out the house has knob and tube (k&t) wiring, now that stress has been amplified.

If the house you are looking at is an older house, it could have knob and tube wiring. Just because the home has k&t wiring, it doesn’t mean the house is in imminent danger of burning down. If the wiring has been well maintained and hasn’t been used as a clothesline in the basement, it may be just fine.

What is knob and tube wiring?

You will not see any k&t wiring in newer homes, but if your home was built in 1950 or earlier, take a look in the basement. If you notice wires running through porcelain cylinders or “tubes” inserted in holes in the wooden floor joists, you have knob and tube wiring. You’ll also see porcelain “knobs,” which keep the wires secure, and prevent them from touching the wood along which the wires run. The wires are usually insulated with a rubberized cloth fabric.

One of the main differences between knob and tube wiring versus modern wiring is the lack of ground wire. Because of this, k&t wiring cannot accommodate any electrical items with three pronged plugs. Additionally, the risk of shocks and fire is much greater. Secondly, the material used to insulate the wire is different. Modern wire uses plastic where k&t uses rubber. The rubber breaks down over time and becomes brittle which is frequently the reason for overheating or mechanical abuse.

Issues with knob and tube wiring

Insulation over the wiring:

With the wiring being coated in a rubber/cloth insulation, it needs lots of space to dissipate the heat that builds up when an electrical current is flowing through. If these wires are surrounded by housing insulation, it is a fire waiting to happen.

Excess use:

When knob and tube wiring was first used there were very few electrical appliances in the average house. Nowadays, with people having more appliances on a circuit, the system can easily become over heated. These k&t systems where never designed to handle the demand for electricity in the modern world.


As it’s such an old system, proper replacement parts are not always available, which could be the reason a lot of makeshift handyman fixes are so dangerous. Knob and tube wiring is easily accessed in the basement, which is perhaps the reason why this wiring is often spliced unsafely with modern wiring by home handymen, as opposed to certified electricians.


Serious problems can occur if this type of wiring is damaged, either due to wear and tear, handyman fixes, or other types of damage. Porcelain knobs and tubes can crack, and the wires tend to sag and fray over time exposing live wires.

Brittle insulation:

As mentioned above, the rubberized cloth insulation on k&t wiring becomes brittle over time, and can flake off. This then leaves the bare wire exposed.

Possible issues obtaining home insurance

When shopping for home insurance, the insurance company will always want to know what time of wiring your home has. Some companies will refuse to insure you if your house has k&t wiring. This is because they consider the risk to be too high. However, there are companies that will insure you home but at a higher premium or deductible. Additionally, they may require an electrical inspection done by a professional before coverage can be offered. If you have an questions regarding obtaining home insurance and other things to look out for, check out our home insurance red flag checklist.

If you have an questions regarding knob and tube wiring or are wondering if your house has it, don’t hesitate to reach out to Beth and Ryan. They would be happy to help answer any questions you may have and direct you to a trusted electrical professional.