So a wire has to be sized to safely carry whatever X load is at Y temperature in Z situation. How much current any given wire can carry depends on A) the wire type (copper, aluminum, tinned, bare, stranded, etc.), B) the insulation's temperature rating, and C) how you use it.įor instance, a wire that is rated to safely carry 100a in open air might only be safe at a max of 55a if it's used inside an air conditioner or a microwave (called chassis wiring), and that same wire might only be rated to be safe carrying 30a inside of a pipe (conduit) or bundled with other wires. So you have to determine what the chart is telling you. The minimum wire size for this will almost always be much larger than a safety chart because starting with 12V or even 24V means you have a lot less margin for error at the load end. Going to a larger wire with, say, 0.015 ohms of resistance reduces this to 1.5V and might be the difference between a radio working or a fridge not cutting out. 50 milliohms), this produces a 5V drop, which means you're feeding 14V on one end and getting 9V on the other. Say a wire is carrying 100A and has a resistance of 0.05 ohms (e.g. That same resistance causes a voltage drop at a certain current. So let's assume you are within the safe zone of the wire itself, the other concern is the capacity of the conductor. Two wire gauges could have two different ratings, so you have to read into the chart to know for sure. Safe handling charts will be functions of the insulation type (various plastics, teflon, silicon, etc) for one and conductor alloy or purity of the copper, e.g. This will be a lower temperature than the wire fusing temp and is the cause of shorts and arcing, which starts fires. a fuse), but more so the temperature where the insulation melts and fails. All wire heats up a little, what you are concerned with is the wire itself heating to the point of failure (e.g. So small currents produce less heat even with a higher resistance. This is a derivative of Ohm's law, power = current ^2 * resistance. Since a wire has a resistance, a given current will produce heat. If you Google parallel resistors you'll see the formula. Stranded wire might confuse you, but this is several smaller wires in parallel, which lowers the equivalent resistance. The larger the diameter (or cross section), the lower its resistance. It has slight resistance that is a function of the diameter of the wire. ![]() Wire is made of a conductor, typically copper, that is not perfect. There are two factors mainly to be concerned with on wire sizing, safety and ratings.
0 Comments
Leave a Reply. |