Wire Gauge and Ampacity
Ampacity is the ability of an electrical wire to carry electric current. An electrical wire that has a small diameter is capable of carrying less electric current than a wire with a large diameter. In North America, wire diameter is commonly expressed in American Wire Gauge, or AWG. A 14 AWG insulated copper wire -- which has a diameter of 1.29 millimeters -- is often used to wire household circuits that will draw 15 amps of current or less. For circuits that will draw up to 20 amps of current, the wire that is most commonly used is 12 AWG insulated copper wire, which is 2.05 millimeters in diameter.
Many electric circuits in a home use one of the two output phases on the home’s transformer. Each output phase provides 120 volts of AC electrical power. However, electric dryers require 240 volts to operate; this requires the dryer to receive power from both phases to receive the full 240 volts. Dryer electrical sockets provide two “hot” connections -- one connected to each phase on the transformer -- to provide the necessary voltage to the dryer.
Dryer Outlets Require Thick Wire
An electric dryer may require as much as 5,000 watts of power. At 240 volts, this appliance would require wiring that is capable of handling more than 20 amps of power continuously. To provide that much electric current without overheating any of the conductor wires, the wires in a dryer electric outlet must be at least 10 AWG, or 2.59 millimeters in thickness. Dryer electrical circuits are often wired with 10 AWG three-conductor (also known as “10/3”) insulated copper wire.
For new electrical circuits, a dryer outlet must have four wires connected to the outlet. These wires are color coded as to function. The red wire is the hot wire coming from the first transformer phase. The black wire is the hot wire coming from the second transformer phase. The white wire is the neutral (or “return”) wire. The bare copper or green wire is the ground wire.
Despite its name, a 10/3 electrical wire contains all four colored wires in the cable assembly.