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:
-
Replace knob and tube circuits with new wiring: Focus on high load areas like the kitchen first. This limits the risk without a full rewire.
-
Use AFCIs: Arc-fault circuit interrupters detect dangerous arcs in old wiring and cut power. Installing AFCIs on knob and tube circuits reduces fire risk.
-
Load shed high demand appliances: Avoid overloading old circuits by moving appliances like refrigerators or clothes dryers to newer circuits.
-
Have an electrician evaluate: Consult a qualified electrician to assess condition and make recommendations. They can identify potential trouble spots.
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:
-
Discoloration or rust on the armored sheathing
-
Exposed copper conductors poking through the sheathing
-
Frequent tripped circuit breakers
Options for remediating BX cable issues include:
-
Localize replacements: Only replace compromised sections of BX cable instead of rewiring the entire circuit.
-
Seal connections: Cover any splices or connections with electrical tape to prevent moisture penetration.
-
Reroute problem circuits: Sometimes the easiest solution is running a new circuit in a more accessible location. Abandon the old BX cable in place.
-
Full rewire: For frequent or widespread issues, biting the bullet and rewiring with modern cable may be your best bet.
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:
-
Brittle, cracked insulation with copper peeking through
-
Discolored wires coated with cloth dust
-
Fuses blowing or breakers tripping frequently
Options for cloth-covered wiring include:
-
Pull new wires through the walls: If the old wires are still intact, you can sometimes use them to pull new, insulated conductors without major demolition.
-
Reroute affected circuits: Run new home runs to replace the most problematic cloth-covered wires. Leave the old wiring abandoned in place.
-
Full rewire: In many cases, a full rewire is the only way to completely eliminate the risks of deteriorated cloth insulation.
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:
-
Cracking, fraying, or unraveling of lead sheathing
-
Presence of bulges or binding in the cable
-
Exposed lead wires emerging through deteriorated sheathing
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!