Electronics: AWG and current ratings - Straight Dope Message Board

Hi all, I'm trying to build the device linked here http://seattlefoodgeek.com/2010/02/d...-for-about-75/ . The internal wiring is in stretches of about 8 inches or so. The author recommends 16-18 AWG wire. I am wondering if this is thick enough to carry the mains-level currents required for this application? The principal current draw is the 3 heaters, which if you search "jc" you'll find a comment that calculates they draw about 7.2A. After searching for the current tolerances of the different wire gauges, I found a bunch of tables like this http://www.powerstream.com/Wire_Size.htm which indicate two values, "Maximum amperes for chassis wiring" and "Maximum amperes for power transmission". What's the difference between these two ratings? My intuition is that the more restrictive "power transmission" rating tells the gauge required to have no significant loss, while the "chassis wiring" rating is the maximum current before the wires start to burn. Is this correct or am I way off? Which number should I be going by? Chassis wiring might (but probably won't) be handling full current all the time. It's things like selector switch wiring, maybe relay wiring, something that sees the maximum current for some non-constant amount of time. Push a button, power goes through the circuit, release the button, power no longer goes through the circuit. Even if it does see the current the whole time it can handle a few more amps because it is used for very short internal runs (a few inches of wire) and doesn't have much of it's own resistance to add to the current draw (and the potential heat buildup). So the wires running power to the heating element are going to see the current draw the entire time the heater is turned on, whereas the wires going to the switch which turned on the heater probably won't (depending on how it's wired).


Current Capacity Of Awg Wire - Bookshelf

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