There are several good reasons to care about whether you have knob & tube wiring:
Knob and tube wiring has not been used in construction since the 1950’s. There has been debate about the safety of knob and tube wiring in older homes – and in Maine, we have a lot of these. On the surface of it, provided that knob & tube was installed properly by a qualified electrician, it doesn’t present a safety hazard. If you’ve had an electrical inspection and know your system is safe, AND you continue to respect the limitations of the system -you could be fine for many additional years. Properly installed and maintained knob & tube wiring can be safe when you don’t overload the electrical system.
How do you know if the electrical system is overloaded? If your home has modern appliances like a microwave oven, computers, central air, newer kitchen appliances, etc. you should have your electrical system inspected to make sure its adequate. Knob and tube was generally installed on 30- or 60-amp services. If you experience a lot of blown fuses, tripped breakers, or electrical shorts, you’re likely exceeding the capacity of your electrical system. Most homes today should be on a 100- to 200-amp service. Be safe – get inspected.
However, even if you aren’t experiencing the problems above, most homes and buildings have experienced some type of renovation or expansion of the electrical system since the original installation of the knob and tube. Problems with knob and tube wiring are generally associated with maintenance of the system, and how upgrades and changes have been accomplished.
With knob and tube wiring, the hot and neutral wires were run separately, a couple of inches apart from each other. As mentioned above, knob-and-tube wiring does not have a ground wire. The copper wires are held by ceramic knobs nailed into the wall studs or floor joists. Ceramic tubes ran through holes drilled in the studs and floor joists. The knobs and tubes protected the wood frame from the heat of the wires. Cloth or rubber was used to insulate the wires — and this is the primary issue with knob and tube wiring. If the electrical system has been abused in any way, the wire insulation will deteriorate leaving bare wires. Bare wires are a fire risk – especially in walls that also contain insulation.
If you have knob & tube wiring, get an electrical inspection to make sure the system is safe. And, for all the reasons above, you may want to consider upgrading the system to meet today’s needs and standards.
If you are interested in reading more on knob & tube wiring, here a few resources you may find helpful:
Knob and Tube Wiring – Yikes! by Amy S Rybacki, Home Renovation Consultant
Knob and Tube Wiring at Living With My Home