nuckolls.bob(at)aeroelect
Guest
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 Posted: Sat Dec 27, 2008 8:29 am Post subject: Is this scheme valid to save weight, add flexibility and |
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At 07:23 PM 12/26/2008, you wrote:
| Quote: |
brianrobertwood(at)gmail. wrote:
> Yep, you are right about that. Small wire=high-resistance=heat
which leads
> to smoke. How hot would a run of #4 get if it were shorted out (batt+ to
> ground)? Would it smoke the insulation?
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Wires are generally really hard to "smoke". This piece of
22AWG wire . . .
http://aeroelectric.com/Pictures/Wire/22AWG_20A.pdf
. . . had been running at 20 AMPS until the temperature
stabilized at 112C. Tefzel is good to 150C. So we're
not even pushing the wire all that hard YET. Of course
we "derate" wires for effects of bundling, hi temperature
environments, and voltage drop. But the point is that
a 22AWG wire we normally limit to a 5 amp circuit feeder
is much more robust with respect to fault tolerance than
the 5A de-rating suggests.
| Quote: | I've run 300A through #4 synthetic rubber insulated welding cable
(105 degrees-C rated) for several minutes without the insulation
smoking or failing. It did get VERY hot though. 
A lot depends on the insulation. PVC is often rated at 85-degrees
C. and will smoke a lot sooner than 400 degree-C rated fiberglass
insulation. The "fusing current" level, at which the copper will
melt and the wire acts like a fuse, is around 800A.
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Which supports the 22 AWG experiment described above.
Folks worry a lot about "smoking" wires but simple
attention to fuses and circuit breakers for small
wires and careful attention to routing and support
for fat wires is all it takes to drive the probability
of smoke down to the very small numbers.
With respect to relative weights, my data books say
4AWG Tefzel (22759/16) is 157 pounds per 1000/ft
or .16 pounds per foot. A 4" chunk of 4AWG welding
cable I have laying around comes in at 24gm or 72gm
per foot which is still .16 pounds. So if you substitute
the style cable I have here (one layer synthetic rubber)
for the 22759/16, there is no weight penalty.
Other brands/styles of welding cable may not be 1:1
but they're not going to be far off. Bottom line is
that any weight differences to be exploited with
exotic combinations of other sizes and subsequent
splices has a poor if not zero return on investment
for $time$ expended.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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