RE: She cannah take tha' mooch pawr-r-r, Cahptain!

["Robert S. Wilkinson" <wilk@domain.elided>]

While the subject of how much current a conductor can handle has been dealt
with, one point that hasn't been emphasized is voltage drop.  The entire
National Electrical Code is based on fire safety, as are most other codes
that specify or recommend conductor size.  To prevent fires or lesser
insulation damage from ohmic heating of wires, 20 A for 12 gauge, 15 for 14
gauge, 30 for 10, etc. are quoted.  But wires drop voltage (in proportion
to their length), which is a somewhat different problem.  At 120 V, loss
of, say, 5 V is negligible.  In a 12 V car, however, loss of 5 V is
disaster.  For example, the wiring to the fuel pump on Spica cars is safe
(big enough), but the pump could benefit from bigger wire to get more
voltage (most people also add a relay).  For lighting, it also makes a big
difference.  If a halogen filament gets 12 V instead of 13, (92% of the
voltage) there is a loss of power in proportion to the voltage squared--you
get 144/169 of what you'd get at 13 volts, or only 85% power
(approximately, as tungsten filaments are nonlinear resistors).  Not only
that, but the color temperature goes down drastically.  Same with audio
systems--that's why thick wire to power the amp, plus to drive the
speakers, is considered worthwhile (although people go way overboard here).
 So in deciding on wire gauges, there's benefit in going quite a bit larger
than what is adequate from a safety point of view, particularly if the wire
is long.

Bob Wilkinson
72 Spider

Where my experience falls short is i'm not sure how much current you can
safely draw through 12 gauge wire, but i'd think it can take 30 amps. any
EE types who can answer that?
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