Re: MOV lightning arrestor in place of safety gap...MCOV?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FIFTYGUY@xxxxxxx 

In a message dated 5/1/05 1:53:48 PM Eastern Daylight Time, 
tesla@xxxxxxxxxx writes:
These 'Arrestors' sound like a good idea, but, do they have a limited life
as with small MOVs , ? , they can only take so many hits ?

    I wonder the same thing:
    From my limited understanding, a MOV is typically works by boundary 
layers between particles of zinc oxide. If the clamp voltage of an MOV is 
exceeded, and enough current flows through the MOV, some particles fuse 
together and thus eliminate boundaries. Thereafter, the clamp voltage of 
the MOV has been changed.
    I've seen a spec that a MOV is within "standard" tolerance if the 
clamp voltage is still within 10% of the original spec at 1mA current. I 
suppose big arrestors may have different construction and tolerances? In 
any event, it seems even if the clamp voltage point has moved, it doesn't 
mean an MOV is useless... just that it's got a new voltage spec.
    So the wise thing to do would be to gently test the clamp voltage of 
any surplus MOV unit one wishes to use, to make sure it still does what 
it's supposed to when it's supposed to.

-Phil LaBudde