Wire Type and Sizing Considerations

Last Updated on Thursday, 12 November 2009 01:40 Written by Richard Friday, 12 December 2008 05:07

Tags:

Wire Type and Sizing Considerations

wire type and size, hvac electrical wiring, wire sizing

Sometimes it necessary for HVAC technicians to know what size and type of wire to use for the job and application. Sometimes it is necessary to call and electrician and ask them what the right size would be. Many HVAC technicians are not trained in electrical considerations such as wire size or type noer do they have access to the National Electrical code as the would have available access to the Mechanical code.

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, 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 Sizing Chart

* 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.

Maximum Ampacity for Copper and Aluminum Wire
Wire Size	Copper		Aluminum
Wire Size	167°F (75°C)	194°F (90°C)	167°F (75°C)	194°F (90°C)
*14	20	25		.
*12	25	30	20	25
*10	35	40	30	35
8	50	55	40	45
6	65	75	50	60
4	85	95	65	75
2	115	130	90	100