Only your local code official can tell you what he will accept. The information given is to discuss the concept. An amperage rating temperature limit would be a limit, IMO, because if the temperature in normal ambients is the rating, the actual temperature would limit the amperage further. The important information is whether you will place insulation above the wire to protect it, or are you trying to keep it inside a hotter space. "My rule of thumb is to go up to 100 ft. at the 60 deg C amp rating (20a for 12ga.) of the wire for 3% or less voltage drop, 1 phase. That's for normal residential wiring where you're allowed 5% total drop from the service entrance. It could put you a hair over 3% in some cases. Also, it's for 120v. For 12v, use 10% of that (10ft., 1 way).
Most of these formulas on the internet are for house wiring or DC applications. Note that DC wiring usually has higher amperages for ea. wire size (often 105 deg C rating) & therefore higher voltage drops. Residential wiring should never use more than the 75 deg C amperage rating (you can't get 90 deg C connectors) AC or DC. The NEC tells you how to allow for ambient or conduit (as opposed to "in air").
" http://www.fieldlines.com/story/2003/7/20/155947/196 "General purpose wiring forlighting and power - residential, commercial, industrial buildings in accordance with the NEC, maximum conductor temperature of 75°C in wet or dry locations, for circuits not exceeding 600 volts" http://www.thomasregister.com/olc/17044454/sectionb.htm |
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