When choosing an size of the wire for an electrical installation, the size of the wire must be chosen correctly to prevent electrical hazards. Many peoples feel that any wire can carry any amount of current. However, the amount of current that pass through a wire must be matched to the size of the wire.
The gauge of the wire is a measurement of the thickness of the wire. The gauge of the wire will determine the amount of current that the wire can carry without overheating. Using a wire that has too thin a gauge for the amount of current that will pass through it will create excess heats in the wire.
How to Choose the Right Wire Size
The excess heat will cause the wire to fail. The table to the right provide the gauge of wire needed for specific amount of current for different lengths of wire. The electrical current passing through the copper conductor of the wire creates excessive heat.
The thinner the wire, the less copper there is to dissipate the heat created by the current. Thus, a thin wire will heat up to high temperatures much more quick than a thick wire. A thick wire has more copper in the conductor of the wire to dissipate the heat created by the current.
Therefore, a thick wire can carry more current before overheating than a thin wire. For these reason, the size of the wire must match the amount of current in the circuit. It is never appropriate to use scrap wire to perform electrical installation.
Furthermore, it is also never appropriate to guess at the size of wire for an electrical installation. Guessing at the wire size can lead to overheating of the wire. Another critical consideration in choosing the size of the wire is the temperature rating of the insulation for the wire.
The temperature rating of the insulation will determine the amount of current that the wire can carry. The insulation for the wire is the material that is wrapped around the conductor of the wire. The insulation for the wire has a maximum temperature that it will not exceed.
If the temperature of the wire reach the temperature rating of the insulation, the insulation will degrade. The degradation of the insulation will create electrical failure. For these reasons, the wire must be sized according to the lowest temperature rating for the electrical circuit.
For instance, if the breaker is rated for a lower temperature than the wire, the temperature rating of the breaker for the circuit must be used to determine the size of the wire for the electrical circuit. The material that the wire is made of will affect the size of the wire that is used in an electrical circuit. For example, copper conduct electricity more efficiently than aluminum.
Due to the higher efficiency of copper in conducting electricity, a smaller gauge of copper wire may be used to carry the same amount of current as an aluminum wire. Aluminum is more often used in electrical service entrance cables because aluminum is lighter and less expensive than copper. However, because aluminum does not carry as much electrical current as copper, a larger gauge of aluminum wire are required to carry the same amount of current as copper wire.
Furthermore, the chart to the right displays the ratings for copper wire. Thus, if aluminum is to be used in an electrical circuit, the size of the wire must be adjusted according to the efficiency of aluminum in conducting electrical current. Using copper in place of aluminum without adjusting the gauge of the wire will cause the aluminum to not be able to carry the electrical current required for the circuit.
The environment in which the wire will be installed and how the wire is installed will also reduce the current that can pass through the wire. For instance, if many wires are bundled together in a group, the wires will not be able to dissipate the heat as efficiently as if they were installed individually. Thus, if many wires are bundled together in a group, the ampacity of the wires will be less than if the wires were installed individually.
Furthermore, if the wire is installed in an area that is very hot, such as an attic, the ambient heat will increase the temperature of the wire. Thus, if the wire is too hot in general, the safe ampacity of the wire will be less than if it were installed in an area that did not reach such high temperature. Furthermore, for electrical circuits that are very long, there will be a voltage drop along the wire run.
This voltage drop may cause electrical issues with device that are connected to the circuit, such as motors struggling to turn or lights in the circuit being dim. For these reasons, the size of the wire should be thicker than what is illustrated in the chart for electrical installations that are very long. For electrical installations that are continuously loaded, such as house circuits that are continuously lit or appliances that are continuously on, the wire must be sized according to a larger gauge.
Continuous loads are those that are installed to run at or near their maximum input for a period of more than three hours. For these loads, the wires in the circuit will experience a gradual buildup of heat. Thus, to prevent heat buildup in the wires, the gauge of the wire and the breaker must be sized for 125 percent of the actual load.
Rather than sizing the wire for the electrical load of the circuit, sizing it to 125 percent of that load creates a safety margin for the wires. Furthermore, preventing the wire from working at 100 percent of its limit for the circuit will protect the insulation and connection for the wire. In creating electrical circuits for electrical appliances, several factors must be considered.
The gauge of the wire, the temperature rating of the insulation, the material of the wire, the environment in which it will be installed, the distance in which the wire will run, and the type of load that will be used in the circuit all must be considered when selecting the size of the wire. For these reasons, wire size cannot be chosen according to the nameplate of the appliance alone. While the chart to the right will help to determine the gauge of copper wire that should be used in an electrical installation, additional rules must also be followed for installations that used aluminum wire, heat, distance, and electrical loads that are continuously running at full capacity.
By following each of these rules, the size of the wire will be ensured to be correct, and the danger of using the wrong size wire can be eliminated.
