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Re: [TowerTalk] MOVs in Stackmatch

To: Pete Smith <>
Subject: Re: [TowerTalk] MOVs in Stackmatch
From: "Roger (K8RI)" <>
Date: Wed, 03 Jun 2009 17:44:10 -0400
List-post: <">>

Pete Smith wrote:
> I am repairing a Stackmatch that was damaged by voltage induced on 
> the control lines by a nearby lightning hit.  Most of the traces 
> going from the terminal strip to the hot side of the MOVs protecting 
> the relay coils are gone.  Do MOVs fail open or closed? 
The straight answer is ...Yes.
MOVs fail in both modes.  Typically I've seen the smaller ones do both 
depending on the strength of the surge.
All of the large ones failed leaving nothing but a pair of leads where 
they used to be located.

GE had a fairly large manual that included the theory of operation, 
manufacture, and use of MOVs. It may be on-line, but I've never looked 
for it.  The book is in the large format about the size of QST but of 
much heavier paper and maybe a 1/2" thick. is 
similar and most likely a lot more than you ever wanted to know about 


Roger (K8RI)
>  Is there any 
> way with minimal equipment to see if an MOV is still good? The relay 
> coils all appear OK, so I guess they did their job.
> 73, Pete N4ZR
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