Light Fixture Wire Sizing for Beginners Light Fixture Wire Sizing for Beginners

Determining the right light fixture wire size is important to ensure the safety of all the home's inhabitants, including the home itself. Currently, the American Gauge Wire system is the standard used in sizing electrical wires. In general, the higher the amperes, the bigger the wires needed. Utility pole wires carry hundreds of amperes, so naturally it will require thicker wires, while household appliances and lighting fixtures only need thin wires since they generally carry low current.

Wire Size and Wire Ampicity

Wire ampicity is the recommended amount of current that can run through a wire without it melting, catching fire or getting dangerously hot. You need to match wire size with rated ampicity to ensure safety and efficiency. Wire gauge or size can be found printed on wires. You will normally see number series labels such as 12-3 and 14-2 on wires: the first number is the wire gauge.

More Factors That Influence Wire Size

Other factors that affect wire size are length and wire type. If your wiring circuit length is in excess of 50 feet, you will need a larger gauge wire. There are various types of wires, such as outdoor wires, weatherproof wires, cable wires, to name a few. Light fixture wires generally are standard copper wiring since they are mostly installed indoors.

Light Fixture Wiring Circuits

Light fixture wiring circuits are not as simple as wiring found in household devices, so finding the right wiring size for them can be a bit more tedious. For example, a microwave that only uses one dedicated wire typically has a rated ampicity of 20 amps; following the American Gauge Wire system as guide, you would find that 20 amps requires a size 12 wire.

With lighting fixture circuits, you have to take into consideration the voltage capacity of the circuit and the wattage of all the lighting fixtures that run through the circuits to get the recommended wire size. In a 120-volt circuit, you add up the total wattages of the light fixtures on that circuit and divide that by 120. You then use the resulting quotient to research for the recommended wire size according to a recognized electrical reference chart such as the Audel Mechanical Trades Pocket Manual or Ugly’s Electrical Reference.

As an example, you have eight incandescent bulbs, each with a wattage of 100 watts that run through a 120-volt circuit. First get the sum of the wattage of all the five bulbs, which is 800 watts. Then divide 800 watts by 120 to get 6.7. Using the Audel Mechanical Trades Pocket Manual as a reference, you will find that the equivalent rated ampicity rating of the resulting quotient is 15, which would require a 14 wire.

As wire sizing involves electricity, it is important that safety precautions are observed to avoid accidents or injuries. If you are unsure about certain procedures, it is highly recommended that you seek the services of a highly trained professional to assist you.

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