As remodeling contractors we've often peeked inside the wall cavities of homes...old and new. Some of the older ones date back to when electrical wiring first was installed. What a joy to see how it was once done, how it now is done, and to be able to compare them. It is intriguing to witness changes over the years, as researchers, manufacturers, tradespersons and lawmakers have combined to do things more safely and sensibly. They really don't build them like they used to...they build them much better now.

Electric wiring has always been mostly copper. Other metals have been tried, but copper seems to work best. It is reasonably soft, making it easy to bend around corners, and it conducts electricity well. The antique wire that we've seen installed was almost all copper...pretty much the same copper that is being used today; but there are other major differences. The diameter of the copper, the distance that it is allowed to travel in a circuit, fuse size, how much load a given circuit is allowed to carry, grounding, sheathing quality (which insulates against shorts) and other factors have drastically improved performance and safety of electrical circuitry.

There are stringent regulations about how many wires can be in an electrical junction box. The relationship has to do with the amount of air space that is needed for a given number of wire connections to properly cool. Or, the amount of air space needed to prevent a given number of wires from overheating and causing a fire.

When you go looking for a length of wire in the electrical department of your local hardware store you might see the term "nonmetallic cable." It's not nonmetallic wire. It refers to the casing or sheathing. That's right, some wire comes in a metal casing and some have a plastic or rubber nonmetallic (NM) casing. NM cable is the most common kind of electric cable used in homes. In one city where we worked, homes are required to be wired with metallic cable. Check with your building department before you begin any wiring. Also, be sure that the casing material that surrounds the wire is approved by the building code. The casing description or "code" will be on the box. "THHN," for example, specifies the type of casing that covers the wire. We have been in stores that had wire for sale that was illegal (and unsafe) to install in a home.

When thermo-coupled recessed light fixtures became mandatory, we witnessed stores selling the old-fashioned and outdated (and illegal) kind by the case. That's probably because they weren't illegal to sell...only illegal to install. Makes you wonder how many unwary consumers were duped by dopey clerks and money-hungry proprietors.

It also is important to know how to properly prepare the end of an electric cable so that a top-notch connection can be made. There are several steps:

* Strip the outside casing

* Remove the paper wrap

* Strip the individual wire casings

* Cut the wire squarely

* Expose the correct amount of wire

The outside casing can be removed by pulling a cable stripper along the length of the cable. Be careful here. Some types of encased wire run parallel while others are twisted. Using a cable stripper on a wire housing where twisted wires exist could cut across the individual wire casings into the protective casing beneath. We use a razor knife at its most shallow setting, slowly cutting between the wires below. Next, remove all the paper wrapping back to the same point as the outside casing. One thing you don't want in an electrical box is paper.

Note: Wire nuts are used to make most modern wire connections. It really is important that the end of each wire be squarely cut and straight. It is far more difficult to perform this simple connecting task when the end of the wires to be tied together are not straight and square.

Finally, don't whittle the covering off the individual wires. Instead, use an approved wire stripper. The cutting edge of the stripper is designed to take the covering off the wire without cutting the wire itself. Even the slightest nick in copper wire can cause an eventual break. In that respect, copper wire is like glass. All you have to do to make two pieces is slightly notch the surface. But, with glass that's a good thing.

Cut the casing back about three-quarters of an inch. That's the length that works best with wire nuts...enough exposed wire to make a connection, but not so much that the wire can't be completely covered by the wire nut.

*Corrective

In a recent column about building a doghouse, we recommended using pressure-treated wood for all framing to enhance lasting quality.

However, we inadvertently omitted the recommendation to use new pressure-treated woods which do not contain CCA (Chromated Copper Arsenate). Newer preservatives and pressure treatments such as ACQ Preserve, NatureWood and Wolmanized Natural Select, which are now available, do not contain arsenic or other toxic chemicals and are fully approved for all residential uses by the Environmental Protection Agency (EPA).

Also, redwood and cedar have natural pest-resistant properties that can be used in lieu of the new generation of pressure-treated materials.