At 05:30 PM 8/31/2009, Rocket J Squirrel wrote: >The differences between your ampacity chart and the one I referred to >might be what one can expect stranded wire (which has less copper >cross-section) versus solid-core wire. Also maybe different DC vs AC, 12v vs 120, wire in free air vs in a bundle, type of insulation, different applications, different codes.
>But the writer talked about how current is carried on the surface of the >wire and he right -- at high frequencies, I've never heard anyone describe >a "skin effect" at DC, so I am not certain whether that writer knows his >onions or not. No skin effect at DC. It starts to have a perceptible though slight effect at audio frequencies. Hams working on 6-meters (~55 Mhz) or higher often use silver-plated copper tubing cause they can get a lot of surface that way.
>If in doubt, when looking at two ampacity charts, use the one that is more >conservative. Your chart shows 8 gauge capable of carrying 150A for "short >runs" at 12v and 46A at 110V, and the difference must be due either to >worrying about heating effects Heating effects is what ampacity is all about -- that's why it's more or less length-independent but changes when you change insulation or start bundling wires together.
-- David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/ '89 Po' White Star "Scamp" |
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