3 worrisome areas for old wiring

Perhaps nothing flashes a warning light more about an old house than the word "electricity." Antique and aging circuits can be cause for concern. Here are three "hot-button" electrical considerations when looking to buy an old home.

1. Knob and tube

Houses built before the '30s may still have what is called knob-and-tube wiring (K&T), in which individual wires are run from porcelain knob to knob and through porcelain tubes in studs, similar to what you might find on an old electrified fence. There is no ground wire, just the hot wire and the neutral; hence there will be no three-prong receptacles.

The best way to check for K&T wiring is to pop your head into the attic, says Howard Maxfield, a longtime home inspector in the greater Seattle area.

Nowadays, an old house with K&T wiring is rare; the wiring carries many problems and the house probably already has been rewired. Lenders don't like K&T and some insurers won't touch it. Some old traditionalists may argue that as long as the wiring is not deteriorating, K&T works just fine; however, most experts nowadays recommend ditching the old wiring.

Among the concerns about K&T wiring are these three:

1. Many jurisdictions won't let you cover K&T with insulation because of heat buildup, so how do you insulate?
2. K&T wasn't designed to carry the heavy electrical loads of a modern household. When the house was built, maybe the electricity had to power a few light bulbs and the fireside radio; today you may have several televisions, computers, a furnace, ovens, microwaves and other major kitchen appliances, shavers, hair dryers, curling irons and any number of handheld power tools.
3. The insulation on K&T wiring can turn brittle and fall off if disturbed.

2. The next phase

The successor to K&T wiring was a two-wire bundle insulated with rubber and fabric. By now, that insulation could be deteriorating. Like K&T, it did not carry a ground wire and had no three-prong receptacles. Not only that, the service panel is still likely to be too small for modern needs.

This wire evolved into the modern bundled wire, often called by the trade name, Romex, which is three wires -- hot, neutral and ground -- encased in a plastic shield.

3. Concerns about the service panel

An old house that has not been updated will have the old fuse box instead of a circuit-breaker box. Even in the unlikely chance that the fuse box is large enough for the modern electrical demand, the need to keep spare fuses of all sizes, and replace them in the dark, is downright inconvenient.

Some owners of fuse-box houses, tired of replacing fuses and perhaps also harboring a death wish, might install a fuse rated higher than the circuit is designed for -- say, a 20-amp fuse in a 15-amp hole. The owner can certainly increase the electrical load for his house that way -- until he burns the place down.

More circuits may have been added to the panel, pushing it beyond its rating. Old houses may have 100-amp panels and the total amperage in the box should not exceed that; the standard for an average house today is 200 amps.

Even if a house has been rewired, you should look at the service panel to make sure the simple things are correct. Maybe the owner's consummate do-it-yourselfer, third cousin did the rewiring, and he made a few mistakes.

• A 15-amp circuit uses 14-gauge wire, but a 20-amp circuit must be at least 12-gauge. (The smaller number means thicker wire).
• Lights usually are on 15-amp circuits.
• A laundry room, bathroom and kitchen need 20-amp circuits for receptacles (two circuits for the kitchen), though other rooms may have 15-amp receptacles.
• An electric clothes dryer should be on a 30-amp circuit with 10-gauge wire.
• Any circuit that may be exposed to water (laundry, bathroom, kitchen, garage and exterior) is to be on ground-fault-circuit interrupts (GFCI).
• Today all bedrooms are supposed to be on arc-fault-interrupt circuits.

These are just some of the electrical problem areas common in old homes. It's good to have an idea of what is right and wrong when you are house-shopping, but you still need a professional inspection before money changes hands.