Knob and tube wiring is an older type of electrical wiring that's no longer used and generally not considered safe. However, some homes still have it, or may have a knob and tube wiring system that was incorrectly modified or rigged to work with a modern electrical system. Knob and tube wiring may contain asbestos insulation, but the only way to know is to have the material professionally tested.

Asbestos was most commonly produced and integrated into building products from the 1920s to the late 1980s. In reality, asbestos use should have ceased much sooner because asbestos was linked to cancer in studies produced as early as the 1950s. You can even extend that number past the 1980s due to stockpiled materials and because some countries treat asbestos use differently. It may also be found more in commercial applications than residential.

Asbestos is a carcinogen, meaning it increases the risk of cancer. Inhaling asbestos fibers is linked to several respiratory issues, including asbestosis, or scarring on the lungs, lung cancer, and mesothelioma, another type of cancer. There's also a link between asbestos exposure and an increased risk of colon cancer and other cancers of the digestive system.

Usually, the people most at risk for disease related to asbestos exposure are those who spend a lot of time working around the material without protection. Electricians who work with asbestos wire have a higher risk of developing mesothelioma or lung cancer due to their exposure.

If you have an older electrical system with fraying wires and other signs of damage, removal  may be the best course of action. When asbestos begins to break down, it's more likely to become airborne, increasing the risk of health issues when it's inhaled.

However, if the system is in good condition and doesn't have visible signs of wear or damage, leaving it alone may be the safest course of action. An asbestos abatement and removal professional can help you determine the best way to proceed.