Our View of Knob and Tube Wiring

Knob and tube wiring was installed in homes until the 1940's. The name is derived from the small, round, ceramic wire mounts that look like knobs and the ceramic tubes which protect the wire when it's run adjacent or through wooden studs and joists. It is a two-wire system with no ground wire; the hot and neutral wires are run separately to each outlet, switch and fixture. The connections are typically not in junction boxes unless newer wiring has been added to the circuit; thus, knob and tube wiring connections are visible splices that are soldered together and wrapped in electrical tape. Knob and tube wiring was and still is a functional and safe system when maintained properly with appropriate fuse and/or breaker protection.

The Need for More Power

Knob and tube wiring was used before WW II because homes did not require as many circuits or as much power as we need today. It was typically used with 30 or 60-amp service. Today's home is usually built with 200-amp service. The wire size dictates the circuit capacity. Third wire grounding throughout the home was not required until 1965, thus local code occupancy requirements are the same for knob and tube as non-grounded Romex and NM cable. Most of these issues are resolved with GFCI devices.

How to Proceed

We know of no improvement requirements if the knob and tube wiring is installed and used properly. However a significant number of insurance companies now consider it unsafe and a higher risk. They may decline coverage or require a higher premium. We suggest you talk with your home insurance carrier regarding their policy requisites. Based on our inspection experience, special attention should be taken to ensure :

• The wire and insulation has not become brittle due to overheating
• Appropriate fuse or breaker protection has been installed
• Repair or remodeling installed proper connections, junction boxes and sizing
• Proper circuit protection or connections were used to combine new and old wiring

We also suggest that you replace knob and tube wiring whenever possible as part of any remodeling project in order to make the transition to grounded circuits. As always, only fully qualified persons should perform any electrical work if some form of upgrade is desired.