So far nobody has mentioned insulation material. The rating of a cable has
little to do with melting the wire and mostly to do with melting or
softening the insulation which would create a shock and/ or fire hazard.
The same size wire insulated with PVC is allowed to rise to a much lower
temperature compared to insulation of PTFE or numerous other materials. And
what is good or bad for mains circuits will not be the same in a vehicle or
aircraft circuit.
David
G3UNA
----- Original Message -----
From: "Don Wilhelm" <w3...@embarqmail.com>
To: <elecraft@mailman.qth.net>
Sent: Monday, October 07, 2013 11:14 PM
Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11
OK Joe, You are correct. It has been a very long time since I have been
involved with heat related science issues. More current equals more heat
(for a given resistance) has been sufficient for me most of the time
without getting into the exact math.
It is good to know that some folks here still have those formulas on the
top of their heads.
73,
Don W3FPR
On 10/7/2013 5:57 PM, Joe Subich, W4TV wrote:
On 10/7/2013 5:31 PM, Don Wilhelm wrote:
> Geesh, how is that possible - twice the current equals twice as much
> heat and will exceed the capacity of the wire.
Sorry, Don ... twice the current => *four times* the heat. Heat
(energy in Joules) = Watts * seconds. One Joule (one Watt-second)
is 2.78e-7 kW*h
73,
... Joe, W4TV
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