Home & Garden

As the noted theologian Matthew Fox was heard to say, after a year-long, papally-ordered vow of silence, “Now, as I was saying…” 

For those of you who did not follow last-week’s thoughts on early electrical systems, much was said about the overall size of these systems and the somewhat Byzantine elements that make them up, including the scary Frankenstein-style knife switches and the “neutral (or double) fusing” that control these circuits. With your forbearance, let us now continue (or for some, begin) with some talk on the nature of knob and tube wiring. 

If you have a house built before 1950, there is a good chance that it contains some knob and tube wiring. In fact, knob and tube wiring is found in homes running all the way up into the ’60s in some quarters, but was largely wiped out by other types of wiring including B-X armored cable and Romex. These two later forms are fundamentally different from knob and tube in that they are cables or sets of wires in a jacket of metal, fabric or plastic, while knob and tube is a system of wires that run independently to the fixtures in the house, meeting up with opposing wires that complete the various circuits. I’ll be more clear about this as we proceed. 

First, what’s in a name? Why knob and tube? Simply, the knobs and tubes from which we derive the name are insulators. Knobs are surface mounted insulators that nail onto the framing of the house and allow the insulated wires of knob and tube to get tied or sandwiched into place, keeping them snug and safe. The more common sandwiching ones just mentioned are made up of two barrel shapes with a nail passing through both, that when nailed, grip the wire and hold it an inch or two from the wood framing of the house. Tubes allow wires to pass through wooden framing, while keeping the wire away from wood. These do not secure wires, although electricians of your grandfather’s day would tie knots in wires at one end of a tube, thus keeping the wire from being pulled through. 

If it’s not obvious why we insulate wires, it’s because they can get hot. Wires get hot as the load increases as in, say, the case of running an electric heater. The more demand is placed on the system, the more current will flow through the wire and the hotter it gets. This is why we use overcurrent protection such as fuses or breakers. 

Wires get hottest where there is high resistance and resistance is greatest where wires either get smaller (such as in extension cords) or where wires (or other electrical parts) make poor contact with one another (like a failed singles event). Then there is the kind of resistance where people get drunk and sing La Marseillaise while hiding from the Nazis. But I digress. 

Resistance is the bane of electricians and the root cause of most electrical fires, which is why I love knob and tube wiring. Love, you say? But isn’t knob and tube an antiquated wiring from long ago, discarded in favor of safer system? No, I say. It is not. It suffers from the same warrantless ill-repute as many a system usurped by those capable of profiting from the revolt. 

Knob and tube is labor-intensive because it is soldered. And labor costs money. Remember soldering? How old are you now? I’m old enough to remember soldering Heathkit Hobby Radios with my dad and although I never soldered a knob and tube “Western Union” splice. It stunned me, the first time I got a good look at one. Flooded with molten metal, the connection between any two wires in the grid of wiring in these old houses remains just as cool as any other part, if not more so. Typically, it will be junction points, as noted above, that will overheat and lead to sparks or fire. This is why modern wiring connections must take place inside of a junction box.  

Now, junction boxes are pretty smart when we’re ready to be making final connections to switches, lamps or outlets because these connections may have increased resistance for a range of reasons. Not the least of these is that they may be changed over time with little control over diligence. But, where wires are permanently installed in the branches of an electrical system, soldering makes great sense and greatly reduces the need for a “J-box” as we call ‘em. 

Knob and tube systems are also more efficient because they utilize less wire by virtue of their single-path design. By using single conductors, in place of cables, each wire can move on to the next designated site without requiring a trip back to a common junction, as would be the case in modern cable systems.  

Some of what I like about knob and tube is based on observation and not on theory. Having looked at nearly 4,000 houses containing knob and tube, I’ve had ample opportunity to see endemic failures as well as aberrant ones and can site only a tiny number of what I would consider either installer or materials failure. This is a good system and is only lacking in overall size as relates to practical use today.  

Generally, the rubber, cloth-covered insulation on knob and tube wiring tends to be intact and elastic and I’ve yet to see a solder that was pulling apart. The joints are covered with a sticky cloth-covered tape of high quality in nearly every case and it’s rare to see one that’s falling apart. That said, tampering and poorly executed modifications are common.  

The worst of these are those that extend the range of these original circuits. When this is done, it means that the design ratings of the original circuits are violated by being asked to perform tasks beyond their original intent. 

These additions are usually spliced in the modern method of simply twisting wires together (although a wire nut or some tape may have been used) and this connection has higher resistance than the soldered type. Often, the same low-velocity brain that conceived these electrical branches that tap off the existing ones struggles to come up with adequate splicing methods, wire stapling and a range of other creative surprises. So watch out.  

The smarter cookie will leave the knob and tube circuits alone and run new ones from a competent source using modern wiring methods. One elegant result of doing this in an older house is that the new circuits one adds will (and must) be grounded, unlike the original ones. 

Grounding (on outlets, it’s signified by that third roundish prong-hole) isn’t needed for most of your appliances. If you were to lay all your electrical devices out in one place (have you seen those books of people from around the world photographed with all their possessions?) you’d find that only a small fraction have a grounding prong and that most will work just fine in your original two-prong outlets.  

If you add a few new circuits to your old knob and tube system, you will both increase the overall load capacity and accommodate the need for grounding (assuming that you place them where those particular devices live). That list includes major appliances such as dishwashers, refrigerators, microwave ovens and both the washer and dryer, so laundries and kitchens are good places to start. Desktop computers require grounding so one or two new outlets where you place your home office is a good idea too. 

An older knob and tube system can be easily connected to a modern breaker panel by a suitably skilled electrician at the time that new circuits are added. This usually requires an upgrade at the main panel since most older main panels associated with knob and tube lack adequate minimal capacity. 

A last thought that I think is more than a little relevant is the issue of capacity. Current building standards call for every house to be capable of providing 100 amps. This is really quite a lot, although some people will use nearly all the 24,000 watts that this allows. That’s right, this is the same as 240 100-watt bulbs running at the same time or 12 2,000-watt heaters. In practice most people use far less and some use almost none.  

A client of mine some years ago mentioned that he was planning on buying a bicycle powered washing machine. He isn’t the only Berkeley client of mine who’s wading in the shallow end of the grid. Some people just don’t use that much power either by political temperament or by prudence.  

So, when you meet with your electrician, be sure to tell them what you need. There are basic code requirements that they will need to observe but there is, without question, room for choice on your part. Don’t feel that you have to be absorbed by the Borg Collective and bring your entire electrical system up to the most current code. Remember, Resistance (the French kind) is never futile.