Knob and Tube Wiring

What is knob and tube wiring?

Knob and tube electrical wiring is the oldest kind of residential wiring and it is now considered antique in the electrical trade. Porcelain knobs guide the wire along its run while porcelain tubes support the wire as it passes through wooden studs and joists. The old-fashioned wire is insulated by paper- or asbestos-wrap and is designed to be air-cooled.

Knob and tube wiring was state-of-the-art from the early 1900s until around 1950. Knob and tube systems were designed to power simple devices of the early 20th century that did not draw a lot of electricity by today’s standards.

Do I have knob and tube in my house?

If your house was built before 1950, you might have knob and tube in your house and not know it. Because knob & tube wiring is largely hidden behind walls, floors, and ceilings, and because homeowners tend to have done partial electrical upgrades over the years, it is advisable have an electrician visit your house and tell you if you have knob & tube. Signs that knob and tube is present include 2-prong outlets and no junction boxes for electrical devices, although there are more determining factors.

Mr. Electric United States can determine if you have knob and tube in your house.

Is knob and tube wiring safe?

Untouched knob and tube wiring systems are generally safe. Damaged, abused, or otherwise compromised knob and tube wiring systems may be unsafe.

Some potential problems include:

• Improper Splices - Knob and tube wiring systems damaged by improperly done or faulty splices can create a major fire risk.


• Exposed wires - The old-style insulation meant to protect the wires can flake off due to the natural aging process, leaving wire exposed. Abuse can occur by either rodents biting through the insulation or persons mishandling the wires.


• Ungrounded system - Ungrounded knob and tube wiring cannot be used to wire modern grounded electrical outlets. While the science of an ungrounded system is not defective, knob and tube systems compromised to accommodate modern electrical devices may increase shock hazard. Mr. Electric United States can perform an electrical inspection and determine a level of fire risk in your home. Since every system is different, knob and tube wiring are assessed on a case by-case basis.

What is the cost to replace knob and tube wiring?

Knob and tube wiring replacement cost depends on how many circuits and devices are in your home. Mr. Electric United States can provide a free estimate.

I hear re-wiring a house is disruptive and messy. Will my walls look like Swiss cheese?

Mr. Electric United States are knob and tube removal experts. We pride ourselves on maximum respect to our customer’s lives and property – and the absolute minimal amount of holes.

Knob and tube wiring and insurance

Insurance companies may not write a new policy if a house has knob and tube wiring. Check with your insurance provider. Occasionally insurance companies request an electrical inspection. Mr. Electric United States can perform the electrical inspection to determine the percentage of knob and tube in your house and provide a level of fire risk.

Benefits of knob and tube replacement

Modern day electrical standards include improvements to new wire technology, the modern grounded electrical systems, and better wire installation methods. New wire technology, temperature-rated wire contained in a nylon sheath, provides better protection than the old paper-wrapped wires. Properly grounded modern electrical systems minimize shock hazards. Wire installation methods are designed for today’s power consumption. Professional installation of a modern electrical system by Mr. Electric United States, and deactivation of your old knob and tube system, will improve your home’s safety and will often increases your house value. Overall, it is generally considered a worthwhile expense to upgrade and modernize your electrical system.