What is Knob and Tube Wiring? Why You Should Consider Replacing It

At Orr Lighting and Electric, we often get calls from homeowners worried about old electrical systems in their houses—particularly something called knob and tube wiring. If you live in an older home or are considering purchasing one, understanding what knob and tube wiring is, when it was used, and why it’s potentially hazardous is critical for the safety and future of your home.

What is Knob and Tube Wiring?

Knob and tube wiring (often abbreviated as K&T) is an early method of electrical wiring used in homes across the United States from the 1880s through the 1940s. It gets its name from the ceramic “knobs” that secure the wires to wooden framing members, and the ceramic “tubes” that protect the wires as they pass through studs and joists.

The system consists of:

• Single-insulated copper conductors, run separately for hot and neutral lines (no grounding conductor).

• Porcelain knobs to support and keep wires away from contact with wood.

• Porcelain tubes inserted into holes drilled in framing to protect wires from abrasion.

• Splice connections often soldered and wrapped in electrical tape—long before modern junction boxes.

In its time, knob and tube was a clever innovation that allowed electricity to spread into homes safely. However, it was designed in an era before today’s heavy electrical loads.

Why Was It Used, and When?

Knob and tube wiring was state-of-the-art from the 1880s through about the 1940s. After World War II, demand for more electrical appliances (refrigerators, washing machines, televisions) exploded. This led to the adoption of modern NM cable (Romex) systems that included a ground wire and better insulation, rendering K&T obsolete.

Today, most knob and tube wiring is 80 to 140 years old. That’s well beyond the expected life of any electrical system.

Why Is Knob and Tube Wiring Dangerous?

There are several reasons why knob and tube wiring is considered outdated and unsafe by today’s standards.

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No Grounding Conductor

Knob and tube is a two-wire system with no ground. Without a ground wire, there’s a significantly increased risk of electrical shock and fire from faults or damaged appliances.

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Insulation Deterioration

The old rubberized cloth insulation becomes brittle and breaks down with age, exposing bare wires. This poses a direct fire hazard, especially where wires are surrounded by old wood framing.

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Overloaded Circuits

When knob and tube was installed, homes only had a few lights and maybe a radio. Modern homes demand far more power—air conditioning, computers, microwaves, big TVs. This can overload circuits never designed for today’s loads.

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Improper Modifications

Over the years, many knob and tube systems have been illegally spliced into modern wiring by homeowners or unqualified handymen. These connections often lack proper junction boxes or strain relief, dramatically increasing fire risk.

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Insulation Hazards

Modern insulation can’t be installed safely around knob and tube wiring, because these wires were designed to dissipate heat into open air. Covering them can cause overheating and fire.

Why You Should Replace It

Most insurance companies won’t insure homes with active knob and tube wiring. Some refuse policies outright, while others charge high premiums.

Replacing knob and tube wiring with modern grounded wiring:

✅ Increases your family’s safety

✅ Reduces fire and shock risks

✅ Lowers insurance costs

✅ Increases the value and insurability of your home

Trust Orr Lighting and Electric

At Orr Lighting and Electric, we specialize in updating older electrical systems, carefully removing knob and tube wiring and installing modern, code-compliant wiring that will protect your family for decades to come.

If you suspect you have knob and tube wiring, don’t wait. Contact us today for an inspection and let’s make your home safer together.