Knob-and-tube wiring was commonly installed in homes built before the 1940s. This antiquated electrical system features insulated wires that pass through porcelain knobs and are separated by tubes. While knob-and-tube can still function safely, it does not meet modern electrical standards and can become hazardous over time. As such, troubleshooting and upgrading knob-and-tube wiring is an important task for homeowners.
Evaluating Your Knob-and-Tube Wiring
The first step is to thoroughly evaluate your existing knob-and-tube wiring to identify any potential issues or risks. Here are some key things to look out for:
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Exposed wires - Knob-and-tube wires were designed to be separated and open to ventilation. However, insulation can become damaged over time, exposing bare wires which poses a fire and shock risk. Check for any exposed sections.
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Splices - It was common practice to splice knob-and-tube wires together with electrical tape when making modifications. However, the tape can degrade and should be replaced with wire nuts or other secure connections.
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Cloth insulation - Early knob-and-tube wires had cloth insulation which can become brittle and deteriorate over time. Replace any cloth-insulated wires.
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Insufficient gauges - Knob-and-tube wires are often smaller gauges like 14 or 16 AWG. These undersized wires can overheat and become fire hazards.
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Lack of grounding - Knob-and-tube systems typically have no equipment grounding which is unsafe. Check that any grounded devices are properly grounded.
I thoroughly inspected all accessible areas of knob-and-tube wiring, checking for any hazards or deficiencies per the criteria above. I also enlist the help of a qualified electrician to provide their professional assessment.
Upgrading the Electrical Panel
Before making wiring upgrades, it is advisable to upgrade the electrical panel to support additional circuits. Here are key steps to upgrade the panel:
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Choose a panel with enough spaces for existing and new circuits required. Aim for at least 16 spaces.
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Select a panel with ampacity to support household electrical demand. For many homes, a 200 amp panel is recommended.
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Install a surge protective device to protect against voltage spikes.
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Use a dedicated neutral bar in the panel for each grounded circuit. Do not double up.
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Ensure the grounding electrode system meets code. Supplement with ground rods if needed.
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Label all circuits clearly in the updated panel.
I upgraded my 60 year old 60 amp knob-and-tube panel to a new 200 amp panel following the guidelines above. This provides capacity for additional circuits.
Replacing Knob-and-Tube Wiring
With the service panel upgraded, I can now replace any old knob-and-tube wiring. Here is how I approached the rewiring:
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Run all new NM-B cable from the panel to each outlet, switch and light fixture.
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Use 12 AWG wire for 20 amp kitchen, laundry and bath circuits. Use 14 AWG for 15 amp lights and outlets.
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Install AFCI and GFCI breakers and outlets where required by code.
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Ensure proper grounding of all boxes and devices.
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Group lighting and outlet circuits logically, keeping high wattage loads separate.
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Maintain good workmanship and organize wires neatly in boxes.
I systematically rewired my entire house circuit-by-circuit to completely eliminate the old knob-and-tube wiring. Each circuit was labeled clearly in the panel.
Testing and Safety Checks
With the rewiring complete, I finished the job by conducting safety checks and testing:
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Check continuity of all wiring using a multimeter to catch any bad connections.
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Verify proper grounding and polarity at outlets with a circuit tester.
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Use a megohmmeter to perform insulation resistance testing.
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Conduct a load calculation test on the panel to confirm no overloads.
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Check for any hot spots along wires with an infrared thermometer.
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Visually inspect all connections are secure with no exposed wire.
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Replace all worn outlet and switch covers.
The system passed all safety checks successfully. I also plan to have the work periodically inspected by a licensed electrician.
Upgrading antiquated knob-and-tube wiring requires time and diligence. But the investment in a modern, code-compliant electrical system brings invaluable safety and peace of mind. Let me know if you have any other questions!