"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
Tim Wescott fired this volley in
:

I think you're missing the point.


no... I got the point. The real point is you don't know the current
capability of the circuit.

You WILL get the highest heating at the point of highest resistance (or
highest unbalanced inductive reactance) but you usually don't know where
that point is.

Just as a really simplistic example, consider a breaker in series with a
circuit that has (say) .1 ohm across a 220V line. Likely, the _breaker_
will be the point of highest resistance, and the heating will occur
there, not in YOUR "circuit".

You have to know the whole distribution system from end-to-end (at least
from the pole to your device) to know where that point is. That was a
point I didn't make in my original "blanket" statement, and it's the key
one.

LLoyd

You get the highest dissipation in the load when its resistance equals the
resistance of the power source. Actually it's equal impedance in AC
circuits, but inductors don't dissipate power as heat. The source in this
case is the pole transformer. At max load power the voltage across the load
will be half the open-circuit value.

Intuitively if the load's resistance is lower than the source's, the source
limits total power, their currents being equal and P=E*I.. If the load's
resistance higher the current through both is less than if they were equal.
In the limiting cases a dead short's current is whatever the source allows
and its voltage drop is zero, so no power. A very high load resistance
limits the current and thus power to a low value.

When you graph the load power vs resistance with the source resistance and
total voltage constant you get a parabola that peaks at equal resistances.

jsw