Re: MOV's

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

The MOVs in the Terry filter will not just wear out.  They will either last 
forever, or get fried directly.

If used within specs, MOVs will last forever.  Power strips and many 
applications us them to take large hits vastly over their ratings where 
they might only work "once", but they will still save equipment even if the 
MOV is destroyed.

I have seen cases where a MOV tests perfectly good, but the leads were 
blown off buy a single spike ;-))

If they are pounded hard over time, they will fail too.  Normally, they 
last forever.

Cheers,

        Terry

At 04:56 AM 6/12/2005, you wrote:
>     This seems like a good group of people to ask about MOV's, since 
> they're used in NST protective circuits.
>
>     I have seen wildly different views on MOV's out there in engineering 
> land.
>
>     One group maintains MOV's last pretty much forever and replacing 
> things like power strips with MOV's is not necessary.
>
>     Another group maintains that MOV's break down at [whatever] voltage 
> above 120 VAC and the MOV shorts the current across it. This group 
> maintains that whenever this happens, a portion of the MOV's dies, and 
> when all the surface area of the MOV is gone, the thing is useless and 
> must be replaced.
>
>     My own experience is that I've seen them die after fun things like 
> lightning strikes.
>
>     I'm wondering: Could the first group just live in a place without 
> much lightning? I'm in Colorado and we get more than our fair share :-)
>
>     Would this also mean periodic replacement of the MOV's in the Terry 
> Filter?
>
>     Thank you!
>
>
>
>     Dave Small