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Posted by David Combs on July 4, 2008, 8:49 pm
>David Combs wrote:
>> In article
>>> Clamping means limiting the voltage difference between different
>>> circuits or conductors. When MOVs in a typical surge protector turn
>>> on, the voltage difference between the various conductors is kept to
>>> the turn-on threshold of the MOVs, which is typically a few hundred
>>> volts. So, the appliance, instead of seeing a differential voltage of
>>> say 2000 volts between say hot and neutral, only sees a maximum
>>> voltage of 350 volts, which is survivable. Plug -in surge protectors
>>> have this protection between the various conductors passing through
>>> them, AC, phone, etc.
>>
>> My *next* stupid question: what's a MOV?
>.
>http://en.wikipedia.org/wiki/Varistor
>
>MOV = Metal Oxide Varistor
>A varistor is a resistor with a resistance that is not constant.
>
>If you know what a Zener diode is, a MOV is like a bidirectional Zener
>diode.
>
>A MOV tries to limit the voltage across it. As surge voltage rises above
>a characteristic clamp voltage rating, the current rises very rapidly.
>That can result in thousands of amps through the device (for a very
>short time). Most surge suppressors are based on MOVs because MOVs have
>high current and high energy dissipation ratings in a small package, and
>they are cheap.
>
>(Clamp voltage) times (current) times( time) equals energy that is
>absorbed by the MOV as heat. That can produce some damage.
>
>MOVs have an energy rating, which is the max energy the MOV can absorb
>in a single event. After that, they will still function but with further
>hits will degrade.
>
>If the single event energy rating is far above the actual energy hits,
>the cumulative energy rating is far higher than the single event rating.
>With high ratings a plug–in suppressor is not likely to fail.
>
>--
>bud--
Cool!
And for an educational thread, thanks to one and all!
David
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