Fairly common in houses built before 1930, the system uses porcelain insulators (knobs) for running wires through unobstructed spaces.Porcelain tubes protect wires that run through studs and joists.Dear Home Inspector: Our home inspector recommended replacing the knob and tube wiring in our home.But my father-in-law says there's nothing wrong with leaving it alone. CTA When installed correctly knob and tube wiring was, in some ways, superior to current wiring practices.Unfortunately, this system is rarely intact after 80 or so years of use.Things that happen well after the original installation can cause major problems. Before I explain the problems, let's examine this old type of wiring.The advice my family once got from an electrician on this question was that if you have low amperage service and NEVER touch it, you're probably okay.
Granted that advice was about 15 years ago and none of that wiring is improving with age. It's very likely that you will introduce a problem between the coating and the wire.
See section 210-7(d)(3) of the National Electrical Code.
If you actually need grounding, I'm afraid there are no shortcuts: you will have to rewire.
Can I replace an outlet that uses knob and tube wiring with a grounded outlet?
Obviously the best choice would be to replace the old wiring. Do I need to run a wire back to the circuit breaker box?
However, many electricians opt to install ground fault circuit interrupters (GFCIs) so there will be some three-pronged outlets.
GFCIs can trip when they sense an imbalance between the hot and neutral wires.
If you're concerned at all, turn off the affected circuits, and get rid of it. The other time you really really should replace it is if it runs through insulation, especially blown-in cellulose. Knob and tube was designed to use open space as an insulator.
In theory it is treated with some awful chemical to make it fire resistant.
Electricians no longer use the knob and tube method to wire houses, and it's widely believed to pose a hidden risk to homeowners.
So, is knob and tube wiring safe or do you need to hire a professional to rip out and replace your existing system? Knob and tube wiring was the go-to method for electricians in the United States from the 1880s to the late 1930s.