RE: 30 amps on 12 gauge

[Jon Pike <jhpike@domain.elided>]

> Per the wire specs at www.alphawire.com, AWG 12 wire with 7/20 stranding has
> DC resistance of 1.5 ohms per 1000 ft.  That means that 2.4 ft has a
> resistance of 0.0036 ohms.  The voltage drop with 30 amps (V=IR) would be
> 0.11 volts, which is only 0.9% of 12 V.  The wire will dissipate 1.35 watts
> per foot (P=VI) - not enough to cook on, but it will heat the wire.
After the many good responses to the question,  I wished I'd gone into 
more detail myself..

Yes, it's good engineering practice to not be right up against the 
limits..  so doubling/dividing the wire,
especially dividing the fuse load and doubling the relays,  is probably 
worth doing.

In all this scaling the wire and fuses discussion,  another important 
issue came to mind.  If you are
going to add wire,  it would be worth researching INSULATION,  and 
getting some that would
be a good choice for auto service,  i.e. higher temp,  and possibly even 
oil resistant.

There's a world of different wire insulation types..  getting something 
durable, especially for under the
hood duty would be worth paying a little bit more.  Don't have any 
suggestions off the top of my head,
but a site like Alpha's would be a good place to research..

Jon
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