Re: Lightning Strike and surge

david <none@xxxxxxxxxx> wrote:

On Sat, 02 Aug 2008 04:27:53 +0000, John Doe rearranged some
electrons to say:

david <none@xxxxxxxxxx> wrote:

On Fri, 01 Aug 2008 18:40:37 +0000, John Doe rearranged some
electrons to say:


shunting electricity is not really what protects the circuit.

Incorrect. The surge energy is dissipated in the MOV.

http://en.wikipedia.org/wiki/Varistor

Don't believe everything you read on Wikipedia.

I don't, but this article happens to be correct. You can search
for yourself if you don't believe it.

I have. A MOV regulates the voltage at the circuit's terminals.
Apparently shunting current allows it to do that, but shunting
current is not what protects the device. What protects the device is
regulating voltage at the circuit's terminals.

Since the circuit input and output voltages are the same thanks
to the MOV becoming a short-circuit, destructive current flow
through the protected device is (ideally) prevented.

Incorrect again. The MOV has a low, but non-zero, resistance
once its threshold voltage has been exceeded.

Doesn't have to be zero, it just has to be low enough to limit
voltage at the circuit inputs, and that's how it protects the
circuit.

The MOV clamps the voltage across its terminals at its turn-on
threshold,

The resistance drops dramatically, so it becomes like a closed
switch, a short-circuit, or whatever you want to call it.

threshold which could be more than 400 volts, depending on the
breakdown voltage of the particular device. It is not a short
circuit.

Use whatever terminology you feel like using.



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