Electrical issues in older houses

The wiring in our 19th century farm house seems to be a mixed lot. Some of it is cable with a black covering that looks something like canvas. Some has a metal jacket. There may even be other types of wire in the walls or ceilings that we haven't uncovered yet. When do you know it's time to replace old wiring with more modern materials?

Like plumbing, the electrical distribution system in an old house can become a hodge-podge of parts and pieces over the years as a variety of people -- not all of them professionals -- make patches and repairs.

A plumbing problem can cause quite a mess. An electrical malfunction can kill you or burn your house down.

So my own first and foremost rule of thumb with wiring is to err on the side of caution. Be proactive - that is, fix problems when you find them, even if they seem minor. Buy a good circuit tester and learn to use it.

And, unless you know what you're doing, call in a licensed electrician.

Old cables can get brittle

Old electrical cable can remain functional for a long time as long as it hasn't been damaged and the insulation hasn't become so brittle that it flakes off.

Even knob-and-tube wiring (named for the ceramic insulators that routed wire through wall studs and cavities) still keeping many old houses up and running.

But age catches up with wire. The cloth-covered wire in your house probably dates from the first half of the 20th century. If the insulation fails - because it has become abraded, or chewed by a winter guest in the walls -- a short, an electrical arc and a fire could result.

There are several kinds of electrical cable with a spiral metal jacket. One is metal clad cable which is still used, especially in areas where the cable is exposed to potential damage.

Another is armor clad, or AC, which does not have a separate ground wire inside the metal sleeve. It uses the sleeve itself as the ground and for that reason is often barred in new construction.

The right time to replace old wiring like this is when there are obvious signs of a problem, such as scorch marks on terminals in switches and outlets, missing or damaged insulation and any other condition that might expose you or your house to a live wire.

The many splendors of new wiring

One benefit to replacing outdated cables and receptacles is that you can add grounding wires and three-prong receptacles. Grounded circuits are not only safer but also more convenient.

You can add ground-fault circuit interrupters and arc-fault circuit interrupters, both now required by building codes in new construction. These devices sense problems and shut off the power before you're electrocuted or a fire starts.

In the unlikely event you still have an old fashioned fuse box, you can upgrade to new circuit breaker panel with sufficient capacity - 200 amps is the standard in new construction these days.

Snaking wires through walls and ceilings

We once owned an old house in which a previous owner had installed an alarm system. Every door and window in the house was hard-wired to a control panel.

After years of working on the house I came to know its every dusty crevice and still couldn't figure out how the installer ran wire where he did. I came to think of him admiringly as a magician.

The point is that a good electrician can keep disruptions to your house at a minimum. By drilling discrete holes in top and bottom wall plates and using fish tapes to route wires through wall and ceilings cavities, most of what has to be done to accommodate new wiring can be hidden.