Excerpts from CHAPTER 13

Modernizing Old Wiring

THE WIRING THAT WAS INSTALLED in a house many years earlier, or even as recently as a decade ago, may not be adequate for the job it is called upon to do today. A complete rewiring job is in order—or is it? Do not jump to the conclusion that every outlet must be torn out and every receptacle replaced. Many times a less expensive job will serve the purpose.

If the wiring does not include an equipment grounding conductor, either in the form of a separate grounding conductor or a metallic raceway or cable armor, as is often the case for wiring over forty years old, consider completely rewiring all circuits.

Assuming an equipment grounding conductor is present, is the wiring inadequate because you are using too many lights? too many floor lamps? too many radios and TVs? That is seldom the case. The wiring usually is inadequate because you have added many electrical appliances that were not considered or perhaps were not even on the market at the time of the original wiring job. The installation does not provide enough circuits to operate a wide assortment of small kitchen appliances, plus range, water heater, clothes dryer, room air conditioners and other heavy appliances. Some of these operate on 240-volt circuits, which may not be available; others operate at 120 volts but when plugged into existing circuits they overload those circuits. In addition, the service entrance equipment may be just too small for the load.

To analyze the problem of your particular house, ask yourself this: If you disconnected all the appliances, would you have all the lighting circuits you need? The answer is probably yes, which means that your rewiring job is simplified. You will still have to rewire the house, but probably not as completely as first appeared necessary. Proceed as if you were starting with a house that had never been wired, but leave the existing lighting circuits intact. (These lighting circuits, of course, will include many receptacles used for small loads like a vacuum cleaner, radio, and TV, but not the receptacles for kitchen or laundry appliances.) This chapter discusses the overall plan for modernizing an existing installation, including upgrading to a larger service and adding new circuits. It also offers problem-solving approaches to the specific challenges you are likely to encounter. Everything in previous chapters describes the wiring of buildings while they are being built, which is called “new work.” This chapter describes “old work,” which is the wiring of buildings after they have been completed.

Problems of "Old Work"

There is little difference between old and new work, except that in old work there are a great many problems of carpentry. The problem is to cut an opening where a fixture is to be installed, and another where a switch is to be installed, and then to get the cable inside the wall from one opening to the other with the least amount of work and without tearing up the walls or ceilings more than necessary.

One house to be wired may be five years old, another a hundred years old. Different builders use different methods of carpentry. Every job will be unique. No book can possibly describe all the methods used and all the problems you will meet. Watch buildings while they are being built to get an idea of construction at various points. In old work, good common sense is of more value than many pages of instruction.

In general, old work requires more material because it is often wise to use ten extra feet of cable to avoid cutting extra openings in the walls or to avoid cutting timbers. Many problems can be solved without cutting any openings except the ones to be used for outlet boxes and switch boxes. Others require temporary openings in the wall that must later be repaired. Techniques are given in this chapter for running cable behind walls and ceilings, and for installing boxes, switches, receptacles, and outlets in both lath-and-plaster and drywall construction.

The rest of the chapter covers--