Wire Type and Sizing Considerations

When a professional electrician looks at a job to wire a house or a new circuit in any structure the primary consideration in the wiring job is the size and type of wire to be used for job. The same for a plumber when looking at a job the plumber will size the pipes based on the number of gallons needed to carry the proper amount of water to its destination. If the pipe is too small then the water needed will not reach its destination. This is almost the same for electrical wire except under-sizing electrical wire is dangerous. Electrical wire carries voltage but it is the current rating of the power loads which is the primary factor in determining the size and type of wire to be used for the job. The current or amps, like the water pipe, is measured by how much flow there is in the wire. If the wire is too small and the flow too fast then wire gets hot. If it gets too hot then the insulation melts and a dangerous condition exists. If the wire runs for a prolonged period of time at a higher than rated temperature there are also corrosive effects at terminal connections. Eventually the corrosion and the excessive heat will cause the wire to become brittle. Solid wire will become brittle enough to eventually break off completely while stranded wire will lose strands one strand at a time from this effect. This causes the wire to become smaller and the heat increases. Eventually the current becomes too much for the wire and it breaks off again creating a dangerous condition. The equipment or device being supplied electricity from this wire, when it breaks, ceases to function while a live wire is hanging inside a control panel or other panel. This is why it is very important to properly size electrical wires for any type of electrical work and not to overload existing circuits in homes and businesses. Imagine a wire inside of a wall getting too hot and the insulation melting. This creates a dangerous electrical situation and also is a fire hazard.

Wire Type for the Application 

One other consideration in electrical wiring is choosing the right wire type. This usually refers to the insulation of the wire and its temperature rating. Selecting the approapiate insulation type and temperature rating is important and depnds on the environment and application of where the wire will be used. Romex is an all purpose wire almost used exclusively in residential wiring where the heat is not excessive and the wire is not subject to damage. Each specific type of wire has its own application and temperature rating and must be used in accordance with the NEC (National Electrical Code). Some wire is rated for direct burial underground while other wire is not rated for direct burial and must be used on conduit when run underground. Always refer to the NEC or your local electrical inspector for rules pertaining to the type of wire and the application.  

Wire Sizing Chart

The following chart  shows the proper wire size or wire guage ( awg ) for the desired current or amperage.

* The national electric code (NEC) specifies that the over-current protection device (breaker, fuse, or motor over-load) not exceed 15A for 14 AWG wire, 20A for 12 AGW wire, and 30A for 10 AGW wire.

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