Re: MOVs and surge suppressors

On Aug 22, 10:38 am, "griz...@xxxxxxxxx" <griz...@xxxxxxxxx> wrote:
...
I thought the only way to test a MOV was to send a surge
through it, and then you will only know what condition it was in
before you sent in the surge. What is the circuit diagram for one of
these indicator LEDs, and is this a way to test any MOV or MOV device?

As others have noted, an MOV is 'protected' by a thermal fuse. If a
surge is so large as to cause MOV to vaporize, then a major human
safety threat exist (see scary pictures). A thermal fuse is placed in
series with MOVs in a desperate hope to disconnect an MOV before it
vaporizes Vaporizing MOV is a complete violation of MOV manufacturer
specs AND a human safety threat.

Think about it a minute. MOV is so grossly undersized as to
vaporize or be disconnected. It leaves the appliance to fend for
itself from surges? Yes, the fuse does not disconnect appliances.
Fuse leaves the appliance to protect itself from a surge.

So why is that appliance working while the protector failed? Surge
was too small to overwhelm protection inside the appliance. But MOV
protector was so grossly undersized as to be permanently destroyed.

By undersizing it, a plug-in protector manufacturer gets the naive
to recommend a grossly undersized protector. Effective protectors
earth surges AND remain functional - do not blow the fuse. Any
properly sized protector remains functional after a surge. So that
'failed' protector light says what about the protector? Grossly
undersized?

Another problem when that fuse does not disconnect fast enough:
http://www.hanford.gov/rl/?page=556&parent=554
http://www.westwhitelandfire.com/Articles/Surge%20Protectors.pdf
http://www.ddxg.net/old/surge_protectors.htm
http://www.zerosurge.com/HTML/movs.html
http://tinyurl.com/3x73ol or
http://www.esdjournal.com/techpapr/Pharr/INVESTIGATING%20SURGE%20SUPPRESSOR%20FIRES.doc

IOW many plug-in protectors will fail even on smaller surges to
avoid those scary pictures. Failure also promotes sales among the
naive.

How to test an MOV? Apply a 1 ma current source to it and measure
its voltage. Remember, a vaporized MOV is a complete violation of
manufacturer specifications. MOVs must degrade; never vaporize. When
has an MOV degraded excessively? When that voltage during a 1 ma
current is more than 10% of its rated voltage. See the data***. A
fully degraded MOV remains functional - does not vaporize.

So again, if a surge was so large as to trip that indicator lamp,
then the protector was grossly undersized - completely ineffective.
If a power strip protector is reported defective by its indicator
light, then you have no business buying more of those grossly
undersized devices. Otherwise even the house is a risk per those
scary pictures. See the Gaston County Fire Marshall report to
appreciate the threat - the fifth citation.

.

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