Knob and Tube Wiring

Knob and tube wiring was commonly used in homes built before 1940. This type of wiring consists of single insulated wires running through the framing cavities. Porcelain knobs hold the wires in place, while porcelain tubes protect the wires where they pass through framing members.

While knob and tube wiring was suitable for the electrical loads when it was installed, it can present safety hazards in modern homes. The insulation on the wires often deteriorates over time, increasing the risk of shocks or fires. In addition, knob and tube circuits are often undersized for today's electrical loads.

If your home has knob and tube wiring, the safest solution is to completely rewire the home. However, this can be extremely expensive. Less invasive options include:

Armored Cable (BX)

Armored cable, also known as BX cable, was widely installed between the 1920s through the 1950s. It consists of insulated conductors wrapped in a flexible metal armor.

While BX cable seems rugged, the armor is prone to breakdown over time. This allows moisture into the cable, degrading the insulation. Signs of trouble include:

Options for remediating BX cable issues include:

Cloth-Covered Wiring

From about 1880 to the 1930s, insulated wires with braided cotton or cloth insulation were used. While cloth helps prevent shocks, it easily fray and deteriorates over time.

Trouble signs include:

Options for cloth-covered wiring include:

Lead Wiring

Lead-sheathed wiring was an early form of armored cable used in the late 19th and early 20th centuries. The dangers of lead are now well understood, and these old cables present safety risks.

Signs of trouble include:

The only remedy for old lead wiring is complete removal and replacement. Even if the insulation looks intact, lead dust and fragments can be released from old cables in walls. Full rewiring eliminates this hazard.

I hope this overview gives you a good understanding of the most common obsolete wiring methods found in older homes, and potential solutions for safely updating these outdated electrical systems. Let me know if you need any clarification or have additional questions!