On Mon, 03 Oct 2011 19:09:42 -0500, the renowned "Lloyd E.
Sponenburgh" lloydspinsidemindspring.com wrote:
Brian Lawson fired this volley in
:
A point to note that amazes me some people don't know.... with
electric current, the point of HIGHEST resistance will be the point of
highest heat(ing). Think about it.
I did. It doesn't. I'm a career electrical engineer, now 'converted to
the dark side' (explosives industry).
IF you even understand Ohm's law, consider that a few hundred megohms in
series with (even) a 575V main won't conduct enough current to even warm
up.
That's a "HIGH" resistance. A complete "open" with no conduction at all
would be the "HIGHEST" resistance. And in that case, no current would
flow, at all. No current, no power dissipation -- no heat. So
obviously, the point of highest resistance does NOT create the highest
heat.
Brian is correct, given the assumption of a simple series circuit.
Consider a series circuit of several resistors. It's a series circuit,
so the current is the same in each. The power dissipated by each
resistor is I^2*R. So it's easy to see that the highest value resistor
dissipates the most power. For example, the wires, which have low
resistance, dissipate little power.
Try this, instead -- a resistance of _exactly_ what will dissipate the
maxiumum POWER across a shunt is the one that will be the point of
highest heat(ing). (hint... heat is energy... power dissipated as heat)
That's the answer to a different question. The maximum power you can
deliver is when a resistor is equal to the total source resistance )of
the line, transfomer, etc. If the power line has a 0.2 ohm source
resistance (1200A short circuit current at 240VAC) then the maximum
power would be delivered (until the breaker blows) by a 0.2 ohm load
(144kW dissipated in each of the load and in everything else).
Think about it. If that doesn't work, try looking up Ohm's law and the
power vs. resistance vs. current formulae.
It's a bit amazing to me that the trades still allow this kind of myth to
perpetuate, and even allow them to be the basis of training their
apprentices. But they do; even today, so don't feel deprived.
The Navy was full of this stuff, too. That's one reason why all I ever
wanted out of the Navy was ME.
LLoyd
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
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