Electricity 101

Associated Expert

n. Electric current used or regarded as a source of power.
n. Intense, contagious emotional excitement.

Circuit breaker
n. An automatic switch that stops the flow of electric current in a suddenly overloaded or otherwise abnormally stressed electric circuit.

E-L-E-C-T-R-I-C-I-T-Y is one of those 4 letter words we dare to mutter (ok, so its 11 letters, but work with us here). Yes, electricity can be scary for those of us who have yet to tackle an electrical project, but just like a woman - electricity just needs a little respect!

Projects can range from the simple install-a-dimmer-switch to the more laborious "I'm going to re-wire my entire 1940's bungalow and bring it up to code".If you're just starting out, below are a few great starter projects you can do TODAY.

And here's a BE JANE TIP: Dimmers add value to your home with little cost!
SAFETY TIP:We think you can do it, but if you aren't 100% confident that you can turn off the power to your home before starting your project - then STOP and call either a professional electrician, or your friendly neighborhood handywoman.

Wires: Past & Present

From the circuit breakers or fuses in your main service panel, a network of wires and cables brings power to each receptacle, light fixture and electrical appliance in your home. Unless you are repairing or replacing an appliance or device, these wires remain hidden.

The appearance of the wiring in a home can vary dramatically, depending on the age of the system.

  • Wiring installed in the early part of this century, until about 1940, was covered with a layer of rubberized cloth fabric called "loom", but it had no sheath for additional protection. This wiring was commonly strung along porcelain insulators, which gave it the name of "knob and tube" wiring.
  • Starting in the 1920's, some wiring was manufactured in flexible metal cable. This "Greenfield" or "BX" wiring proved much better than the knob and tube wiring because it shielded the wires from damage. The armored cable on Greenfield wiring lacked a grounding wire; the metal coils of the cable provided the ground.
  • Metal conduit has been installed in many homes since the 1940's. Like Greenfield cable, the metal conduit shell protected wiring and provided a ground. Metal conduit is still recommended by code in some installations, such as exposed wiring in a basement or garage, but modern conduit will use a ground wire.
  • Early NM (nonmetallic) cable was installed from 1930 to about 1965. Early NM, which has no ground wire, has flexible rubberized fabric protecting the wires. Electricians loved it because they did not have to snake individual wires through conduit.
  • Modern NM (nonmetallic) cable, which includes a bare grounding wire, was introduced in 1965. The wire insulation and the outer sheathing is made of plastic vinyl; the gauge of the wire is printed on the sheathing. A "12-2" cable, for example, has two 12 gauge insulated conducting wires. Today almost all home wiring is NM, except where otherwise prohibited by code.
  • UF (underground feeder) cable is designed to be installed in damp conditions. Its wires are embedded I solid-core vinyl sheathing. Like NM cable, it too contains a bare copper grounding wire.

Inside the protective sheathing and insulation, the metal wire used to carry current is usually made of copper. In some houses, however, the wire conductors are aluminum-sometimes clad with copper or nickel. Aluminum or clad-aluminum wires have special safety concerns.

Wires in home circuitry can range from thick, #6 gauge cables, used for large appliances, to very thin #22 gauge wires, used only for low voltage applications, like doorbells.

Wires must be large enough for the amperage rating of the circuit. A wire that is too small and is overloaded can become hot enough to melt its insulation and start a fire. The "ampacity" of wire refers to how much current it can safely carry.

Ampacit varies according to the size of wire and the material used. The chart shown below shows the ampacity of copper wire. Check your home to make certain the gauges of the circuit wires match the circuit ratings, stamped on the circuit breaker or fuse. If not, have an electrician correct the situation immediately. In addition, make sure the total wattage load likely to be placed on the circuit at any one time does not exceed the ratings shown in the third column. The Electrical Code states that the wattage load should never exceed 80% of the full wattage capacity of the circuit. A 15-amp 120volt circuit, for example, has a maximum capacity of 1800 watts (15 x 120), but the load placed on it should be no more than 1440 ( 80% of 1800). Although the wires can safely carry the maximum wattage load, these high loads may eventually cause a circuit breaker to malfunction.

2880 (240 V) Light fixtures, outlets
Room air conditioner, large tools #12 20 amps 1920 (120 V)
3840 (240 v) Light fixtures, outlets, room air conditioner, appliances
Room Air conditioner, large tools #10 30 amps 2880 (120V)
5760 (240 V) Commercial equipment
Clothes dryer #8 40 amps 7680 (240 V) Electric range, central air conditioning #6 55 amps 10560 (240V) Central air conditioning, electric furnace

Important Note About Aluminum Wire
If you find aluminum wire in your home, you need to take special precautions. Aluminum wire is identified by its silver color and by the AL stamp on cable sheathing. Two variations, copper-clad aluminum wire and nickel-clad aluminum wire, have a thin coating of copper or nickel bonded to a solid aluminum core.

During the 1960's and the early 1970's, aluminum wire was installed in many houses, but by the early 1970's, all-aluminum wire was found to be a safety hazard if connected to devices with brass or copper screw terminals. The problem arose because aluminum expands and contracts at a different rate than copper or brass, and can gradually work loose from connections.

For a short while, switches and receptacles with an Underwriters Laboratories (UL) wire compatibility rating of AL-CU were used with both aluminum and copper wiring. Unfortunately, these AL-CU devices also proved to be hazardous. When connected to aluminum wire and copper-clad or nickel-clad aluminum wire.

Since 1971, switches and receptacles designed for use with aluminum wiring were introduced with making CO/ALR. Today this is the only approved device for aluminum wiring.

IMPORTANT: If you have aluminum wiring, you need to replace any switch or receptacle that does not bear the CO/ALR rating stamp. Aluminum wire or clad-aluminum wire is considered safe if proper installation methods are followed, and if the wires are connected to special switches and receptacles designed to be used with aluminum wire. A switch or receptacle that has no wire compatibility rating printed on the mounting strap is designed for use with copper wires only. (If you have copper-clad or nickel-clad aluminum wiring, see an electrician or consult a detailed description of the National Electrical Code for more information.)

But all parts of the system must be up to Code to be safe. If you have any doubts, have a qualified electrical inspector review your system.

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