That's exactly right. They're essentially semiconductors, and their
use as snubbers or clamps bear that out.
Like all semiconductors, they're affected by heat. Since they work by
converting the over-power situation to heat, in effect they kill
themselves slowly with every event.
Citations for this data appear below, in case anybody cares to look at
the original data.
Source: Simple Model of Metal Oxide Varistor for Pspice Simulation,
IEEE Official Publication
URL : http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1336959
---- Original message ----
>Date: Wed, 3 Jun 2009 21:05:16 EDT
>Subject: Re: [TowerTalk] MOVs in Stackmatch
>I was under the impression that MOV devices are "damaged" somewhat during
>each protection event and eventually enough "damage" accumulates and they
>have to be replaced.
>Maybe someone with more knowledge will comment on that.
>If this is the case, it seems that a big hit might use up a lot of the
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