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Re: MOV's

Hi Chris,

At 07:31 PM 02/22/2000 +0000, you wrote:
>As I understand it a MOV (Metal Oxide Varistor) is basically a whomping 
>Zeneer Diode in essance. It does nothing untill you reach a prescribed 
>voltage, then acts as a short circuit. A hogh voltage gate essentially. Am I 
>wrong?

You are about right...

>
>Assumeing I am right (hey, this is my dream remember?) then how is this 
>different than a spark gap?

Once fired, spark gaps stay conducting as long as there is current present
regardless of the voltage.  MOVs will open right back up once the voltage
drops below their rating.  This is good for protection circuits because
they will only clamp when needed thus keeping them cooler than if they
locked into a short.  They will not acts at all right for a spark gap
application.

>
>Do they reset after use? or simply short out and need to be replaced.

They go back to high resistance the instant the voltage goes bellow their
rated voltage.  they can take millions of hits.  In a current limited NST
situation. they will last forever as long as they don't overheat.

>
>If these behaive like a gap, then why use them in place of a gap in an NST 
>protection circuit? pros/cons?

Cheers,

	Terry

>
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