Excerpt from my regular column in the Santa Barbara News-Press.
Question: I live in a beautiful home in San Roque that was built in the late 1920’s and it still has the original Knob & Tube style of electrical wiring. The original fuse box was removed and replaced with a circuit breaker box years ago, and I have not had problems with any of the wiring. I want to add several new electrical outlets and a light fixture and I have heard and read different takes on the safety of adding any additional load to the old wiring. Do you think this is a good idea?
Your Handyman: Prior to around the mid 1930’s the electrical service in homes was provided by the style of wiring referred to as Knob and Tube (K & T) where single insulated copper wires ran through framing studs via porcelain insulating tubes and were supported in runs by nailed down porcelain insulating knobs. When the wire entered an appliance or passed through a wall board to a switch box it was insulated with a flexible cloth sleeving called Loom. This early insulation was typically an asphalt saturated cotton cloth which would eventually be replaced with rubber insulation in later years. Wire splices were simply made by mechanically twisting the wires together and then wrapping the splice with asphalt saturated cloth tape. Knob & Tube wiring had only a black hot wire and a white neutral wire and sometimes fuses were placed on both the hot and neutral line of a circuit which created the dangerous situation of a neutral fuse burning out while the hot leg of the circuit remaining energized. The principles of effective grounding were not fully understood in this time period and the now standard green or bare grounding wire was not part of K & T. Many homes in Santa Barbara still have their original K & T wiring but most all have replaced the old fuses with modern circuit breakers.
I personally would not recommend adding any additional load to your older wiring by installing new outlets or fixtures, however there are many electricians who would disagree with me on this point. You do definitely want to avoid or minimize the use of any high wattage appliances like space heaters, home theater hardware, or a large flat screen TV. The electrical demands of a modern house are much greater than what was required by homes in the 1930’s, many appliances need a ground wire for safe operation, and thus the wiring needs are substantially increased.
If you decide to go ahead with your electrical project be sure to have the work done by a licensed electrician who has experience with K & T wiring. In my opinion it would be a very worthwhile investment for you to have your house rewired with modern wiring and to be done with your old but still functioning K & T. As with any home you want to be sure that you have adequate smoke detectors throughout the house and be careful not to overload the safe capacity of your wiring. I wouldn’t lay awake at night worrying about the safety of your old wiring, but rewiring the house should be something that you place high on the “To Do” list, and would certainly be a sound investment.
Owner, YourHandyman & Construction
CA License #935259