A MOV is somewhat like two back-to-back Zener diodes.
It
is
a voltage clamp.

no,it's not. it does not "clamp" the voltage.

You do not pass energy to ground, you pass
current to ground just like you do with any load. The
energy
is totally dissipated in the MOV.

Uh,"passing current to ground" IS passing energy to
ground.


David




totally wrong.
Wiki has a nice article on metal-oxide varistor,I
suggest
you read it.

--
Jim Yanik
jyanik
at
localnet
dot com

Jim, I am not going to get into a flame war over this
topic.
Maybe you should check this out:

http://www.cliftonlaboratories.com/metal_oxide_varistor_(mov).htm

David



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

Varistors can absorb part of a surge. How much effect this
has on risk to
connected equipment depends on the equipment and details
of the selected
varistor. Varistors do not absorb a significant percentage
of a lightning
strike, as energy that must be conducted elsewhere is many
orders of
magnitude greater than what is absorbed by the small
device.

--
Jim Yanik

This is my final say on this topic. In the quote above, you
assume the section saying that "... energy that must be
conducted elsewhere ..." goes to ground through the MOV.
This is where your error resides. The energy is going
elsewhere but being dissipated somewhere else completely
such as blowing up a transformer. The article should also
use the term dissipated elsewhere to make things clearer.

You also assume that passing current is equivalent to
dissipating energy. Current can *move* energy somewhere, but
electrical energy is only dissipated when the current causes
a voltage drop. A perfect ground will not have a voltage
drop so that is not where the the energy is being
dissipated.

David