of the most popular and proven components in AC mains surge protection
has been the Metal Oxide Varistor (MOV). As with most things in life they
age and this aging is accelerated in high surge areas. As these devices
age the voltage at which they clamp gradually falls until eventually they
fall to the level of the mains supply and overheat. They have in some
circumstances even caught fire! Today's MOVs are coated in a flame retarding
material but this alone does not guarantee safety. This is why
all Zymax MMOV® products are thermally fused.
A number of mains SPDs on the market feature parallel MOVs with one being
smaller and lower energy than the other. When this weaker MOV eventually
fails a warning is provided (usually visually) prompting the user to replace
the device, even though protection (that's better than before) is still
present. This adds to the component cost of the device which is passed
down to the customer. With Zymax MMOV® products
is present for the FULL life of the
The MMOV® product continuously
monitors its protection status through its complete life cycle.
Other products on the market feature LEDs or Neon indicators which
light when there is a failure. With no lamp test facility, how does one
know that the indicator itself has not failed?
Zymax MMOV® products feature a single failsafe
LED indicator which is continuously lit during normal operation.
As the MOVs begin to age the LED will flash indicating that a
replacement device should be at hand. Full protection is still present.
When the MOV nears the end of its useful life an audible alarm sounds
and the LED continues to flash. At this point the protection device should
be replaced. Protection is still present. If the user fails to observe
the warnings and the MOV clamping voltage falls too low the thermal fuses
will protect the device and an audible two tone signal emitted with the
LED extinguished. At this point protection is no longer provided but power
continuity is uninterrupted.
During installation a likely scenario could be that the
engineer failed to strip the insulation properly from the earth wire.
An MMOV® device would prevent this by providing an audible indication
should there be a bad earth connection or the live and neutral wires are
MMOV® devices self check their
connections and will let you know if they are incorrect!
MMOV is a registered trademark and the technology patent