WIRE
SIZE AND TYPE:
The size of wire and its type is the prime consideration when doing
any electrical work. Wires that carry electrical current are similar
to pipes that carry water: the larger its diameter, the more current
(amperes) it can carry. The American Wire Gauge (AWG) system is
the standard system used for measuring wire size (gauge). Gauge
numbers are inverse to their size; thus, for example, No. 12 wire
is smaller than No. 10 wire. Large wire is usually stranded; smaller
gauge wire is usually solid. Nos. 16, 18, and 20 contain multiple
strands twisted or braided together.
No. 12
wire has replaced No. 14 as the standard residential wire, and it
is now required by National code for all new residential wiring
to be No. 12 with ground unless, of course, specified otherwise.
Exceptions to this are the wiring used in lighting fixtures, furnace
controls, doorbells, and other low-energy or amperage circuits.
The electrical
wire in your home may be made from three different types: copper,
copper-clad aluminum, and aluminum. For any project, you should
always use the same type of wire that is installed in your home.
You can determine this by opening a switch or outlet box, pulling
out the wires, and noting the information printed on the insulation.
The method of reading wire markings is given later in this article.
Special
care must be used with aluminum wire. It does not behave like copper
wire. Aluminum wire tends to expand and contract, working itself
loose from terminal screws. This can cause trouble mainly electrical
fires. If your home uses copper clad aluminum wires, do not add
aluminum wire to it. Use copper or copper-clad aluminum wire.
If your
home has aluminum wire, check to make sure that the switches and
receptacles are marked CO/ALR or CU/AL. The CO/ALR marking is used
on switches and receptacles rated up to 20 amps. The CU/AL marking
is used on switches and receptacles rated at more than 20 amps.
If the switches and receptacles do not bear these markings, replace
them with those that do. Never use aluminum wire with any back-wired
switch or receptacle that requires pushing the wire into the device.
Aluminum wire must connect to terminal screws.
Since
recommendations for wire sizes are generally for copper and copper-clad
aluminum wires, you must readjust the designation to the next larger
size when using aluminum wire. For example, if No. 12 copper wire
is recommended but you are using aluminum wire, you must use No.
10 instead.
