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rpiereck

FAQ: Wire gauge selection

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I see on many forums that when people ask "what size wire should I use?" the answer sometimes sounds like either "the biggest the better", or an arbitrary gauge size without basis for the choice. The gauge size might be correct, or not.

 

As an aircraft mechanic, I am obliged to use the proper size wire when I do repairs, and there are guides I must use. These two graphs are good references for making wire selections. For automotive applications, assume the circuit voltage to be 14v for this purpose.

 

This graph is to be used for continuous loads, like driving and fog lights or anything else that must be continuously powered. This chart shows two curvers, 1 and 2, for wire that are either bundled or hanging in free air. That is due to the fact that wires in bundles can't dissipate heat as well as thos hanging in free air. For most add-on automotive applications the cable is hanging in free air (not bundled), so I'd use curve 2.

continuousloads.jpg

 

This one should be used for intermittent loads, such as horns, brake and turn signals, etc.

intermitentloads.jpg

 

These are instructions for using the charts above.

wiregauge.jpg

 

Granted, these are for installation on aircraft, but if it's good enough for an aircraft, must be good enough for a car, imho. I hope this helps anyone trying to determine wire size for any application.

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