What Gauge Electrical Wire Is Needed for Household Lights

Wire Gauge Measurements

• Electrical wire is measured in American Wire Gauge, or AWG. When an electrician says that he has wired something with “14-gauge” wire, the wire diameter will be 14 AWG, or approximately 1.63 millimeters. As the “gauge” number decreases, the diameter increases. For example, an 18 AWG wire has a diameter of 1.02 millimeters, whereas a 12 AWG wire has a diameter nearly twice as wide (2.05 millimeters).

Aluminum Wire vs. Copper Wire

• Copper wire is most commonly used to wire a home. However, some homes contain aluminum wiring. Copper wire is a better electrical conductor than aluminum wire; to conduct the same amount of current as a given copper wire, an aluminum wire must be of larger diameter than the copper wire. For example, a 14 AWG wire with THHN insulation can handle a maximum of 25 amps. To handle the same amount of electric current, an aluminum wire with the same type of insulation must be 12 AWG in diameter.

Light Bulb Current Draw

• Many light bulbs are rated for the amount of electrical power they use. This rating is given in watts. Since the largest factor in determining what gauge of wire to use for wiring a light receptacle is electric current, it is necessary to calculate how much current a light bulb will use. The formula to calculate current is I = P/V, where “I” represents current as measured in amps, “P” represents power as measured in watts and “V” represents circuit voltage. Homes connected to the North American electrical grid are wired for 120 volts AC; therefore, you would divide the power rating by 120 to obtain the number of amps that the light bulb will use. If there will be multiple lights wired to the electrical fixture box, you will have to add together the power rating of each light and then divide that sum by 120 to get the current draw.

Typical Household Light Circuits

• Many household light receptacles are wired to safely accept one or two standard incandescent light bulbs. Many of these fixtures limit each light bulb to a maximum of 100 watts. If there is a light receptacle that uses two 100-watt bulbs, the total power used will be 200 watts. The total current draw for such a circuit is 1.67 amps. Other light receptacles – such as electric chandeliers – may use several light bulbs that do not exceed 30 watts each. If a chandelier has 8 bulbs of this type, this will produce a current draw of 2 amps. For most incandescent lighting circuits of this type, 14 AWG copper wire or 12 AWG aluminum wire would provide sufficient current to operate the lamp.