Rich S wrote:
> quote:
> "MOV surge protectors have little real value. Their main limitation is that
> they are consumed by doing their job and no longer protect anything. That
> may very well be why some events are protected from (the MOV is still
> intact) and some events allow damage to the gear (MOV was sacrificed
> previously, but no one knew). "
>
> per this article:
> ...
> www.electronicdesign.com/power-management/article/21800530/select-the-right-varistors-for-overvoltage-circuit-protection
> ...
> the degradation is in the form of an leakage current. As the MOV is tied
> across the 120VAC or 240VAC, the power dissipation increases, so
> the body temperature increases, I wonder if this temp-rise is reliable enough
> to detect with a few inexpensive parts and alert the owner of impending risk.
>
> I always wondered if a third "sense" terminal would be of any value.
> If the damage leads to a change in internal impedance, then
> the change in AC voltage level from the sense terminal could be
> detected.
>
>
>
>
>

On Monday, 16 January 2023 at 17:38:49 UTC, Les Cargill wrote:
> Rich S wrote:
> > quote:
> > "MOV surge protectors have little real value. Their main limitation is that
> > they are consumed by doing their job and no longer protect anything. That
> > may very well be why some events are protected from (the MOV is still
> > intact) and some events allow damage to the gear (MOV was sacrificed
> > previously, but no one knew). "
> >
> > per this article:
> > ...
> > www.electronicdesign.com/power-management/article/21800530/select-the-right-varistors-for-overvoltage-circuit-protection
> > ...
> > the degradation is in the form of an leakage current. As the MOV is tied
> > across the 120VAC or 240VAC, the power dissipation increases, so
> > the body temperature increases, I wonder if this temp-rise is reliable enough
> > to detect with a few inexpensive parts and alert the owner of impending risk.
> >
> > I always wondered if a third "sense" terminal would be of any value.
> > If the damage leads to a change in internal impedance, then
> > the change in AC voltage level from the sense terminal could be
> > detected.

Here is an example of an SPD (MOV) with both a visual indicator and an
isolated monitoring switch contact.
https://www.tlc-direct.co.uk/Products/WYNMT2SPD3W1.html
John