What is Knob and Tube Wiring?
Knob and tube wiring was commonly installed in homes built before 1930. It consists of insulated copper wiring that is run through the open spaces in walls and ceilings, supported by ceramic knobs and tubes.
The wiring is separated from structural framing and exposed to air circulation, reducing fire hazards from heat buildup. However, knob and tube lacks modern safety features like grounding and fire resistant insulation. It also becomes brittle and dangerous as it ages.
Dangers of Outdated Knob and Tube Wiring
There are several risks associated with outdated knob and tube wiring:
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Fire hazard - The old, cracked insulation can expose bare wires that arc and spark, igniting surrounding materials. Knob and tube wiring lacks grounding, increasing electrocution risks.
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Insufficient for modern loads - Knob and tube was designed for lower wattage lighting and appliances common decades ago. Connecting modern high wattage devices can overload the wiring and cause fires.
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Inability to use circuits fully - Without a ground wire, GFCI (ground fault circuit interrupter) outlets cannot be installed. This prevents powering many useful appliances in bathrooms, kitchens, etc.
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Difficulty obtaining insurance - Most insurers won't cover homes with knob and tube wiring due to the risks. This can make selling or financing the home challenging.
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Lower property value - Outdated wiring is considered a detriment that can lower a home's value significantly compared to similar homes with modern wiring.
Why Knob and Tube Wiring Should Be Replaced
Considering the fire hazards and limitations of knob and tube wiring, experts strongly recommend complete replacement with modern wiring for safety.
Replacing the old wiring enables you to use the full capacity of your electrical system, power sensitive electronics safely, and meet modern building codes. This also makes your home more sellable.
Options for Replacing Knob and Tube Wiring
There are a few options for replacing knob and tube wiring:
Full Rewiring
This involves removing all of the old wiring and installing completely new wiring throughout the house:
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Safest option - Allows the entire electrical system to be brought fully up to modern code.
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Very labor intensive - Wiring must be accessed behind walls and ceilings, which involves extensive demolition and patching.
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Highest cost - Tens of thousands of dollars or more, depending on house size and access complexity.
Pigtailing
The old wiring is left in place but disconnected from circuits. New wiring is spliced to the old and run to outlets and fixtures:
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Faster and cheaper - Doesn't involve as much structural demolition.
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Still upgrades wiring - Allows grounded, GFCI outlets and modern circuits.
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Less ideal - Leaves old brittle wiring in place, some fire risk remains.
circuit breaker panel replacement
Upgrading the main circuit breaker panel without rewiring the whole house:
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Lower cost - Panel upgrade alone can cost $1000 to $3000.
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Safer circuits - Allows installing GFCIs, AFCIs, and grounding.
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Doesn't address old wiring - The existing outdated wiring remains throughout the house.
Safety Precautions When Replacing Knob and Tube Wiring
Replacing old wiring yourself has dangers if proper precautions aren't taken:
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Turn off power at the main breaker - Use a contact voltage tester to ensure power is off before working.
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Follow local permit and inspection requirements - Illegal wiring can put insurance coverage at risk.
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Only take on what you can safely handle - Consider hiring an electrician if the wiring is complex.
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Use caution around lath and plaster walls - The metal mesh can conduct electricity.
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Wear personal protective equipment - Especially goggles and dust masks during demolition.
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Take photographs - Document the existing wiring locations and connections before altering anything.
Hiring an Electrician to Replace Knob and Tube Wiring
Consider hiring a licensed electrician if you lack electrical experience or the wiring is very complex. Benefits include:
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Enables complex wiring tasks - Like installing new boxes, running wiring through finished walls, etc.
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Certified experience - Reduced risk and proper handling of electrical hazards.
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Inspection compliance - Electricians ensure work will pass local inspections.
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Future Issues handled - An electrician will return to address any wiring problems.
Get quotes from multiple electricians before selecting one. Check reviews and verify they are properly licensed and insured.