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Knob and Tube Wiring

If your house was built before WWII and hasn’t been updated or renovated, you probably have knob and tube wiring. Modern house wiring has three to five conductors encased in a tough thermoplastic jacket.

Knob and tube wiring is a single conductor system, the copper is protected by a rubber, fibre type coating which after 50 years or so has begun to break down. Possibly having bare copper exposed. The most dangerous part of knob and tube wiring is when it has been “tapped into” by a “handyman”.


We have seen connections where the original knob and tube insulation has been stripped off and new wiring has been laid beside or twisted around it then taped in place. This is an electrical fire waiting to happen. Another common problem is replacing the original fuse with a larger size fuse. Someone is making toast and boiling water in the electric kettle at the same time and the fuse blows, I know, lets put in a bigger fuse! This solves the problem of the fuse blowing but causes a much more dangerous problem. A copper wire which was designed to safely carry 15 amps of electricity is now carrying 20, 25 or even 30 amps. The wire heats up, this causes the protective insulation around the wire to break down. I have seen knob and tube wiring where one small bend of the wire will cause all the original insulation to fall off. The copper itself is brittle and prone to breakage.

If the knob and tube wiring is in good condition and has not been tampered with, there is a way to make it safe. See solution 2.

Knob and tube wiring also has no bond (sometimes incorrectly referred to as ground) wire, the bare copper wire you see in modern wiring. If the “hot” (black) knob and tube wire touches a copper water line, or any other metal plumbing line and the wires insulation has broken down the metal may become electrified and the fuse or circuit breaker will NOT trip.

There are solutions to make knob and tube wiring safe.

1) The best solution is to remove it and install modern Loomex, Romex NMD type wiring.

2)You can also GFI protect it. This means installing a GFI receptacle or a GFCI breaker as the first device the electricity flows through. Then everything “downstream” is protected. This must be done for each circuit. Your wiring is safe and will be accepted by your insurer.

If you have knob and tube wiring and are concerned about it or would like a free estimate contact us today!