> Why do you need the MOVs? Why not just take the L & N to ground via a gas
> tube each?
Indeed!
Why, even, use any suppressors?
Supposedly, there is only insulation from L and N
to ground (earth). As such, it is easy to achieve
5 kV worth of insulation. Without much effort, this
can go to 10 kV.
5 kV will easily withstand most mains transients.
If there is concern for transient suppression above
this value, simply use an air gap between a pair of
terminals in the circuit. Use the minimum spacing
allowed by the safety standard. Make sure the
terminals are robust and coated with solder. This
way, there will be little or no degradation when an
arc occurs. (The solder may melt, but it will re-
form when it cools.)
We always test mains circuits to breakdown. Most of
our mains circuits go to >5 kV simply by meeting the
standards' requirements for spacings and Y-caps.
Our typical >5 kV breakdowns occur between the terminals
of the Y-caps (on the back side of the PWB, between the
Y-cap leads protruding on the back side).
I am often amused by the commercial "surge suppressors"
offered by computer stores and similar stores. If a
product meets the various "surge" and safety standards,
there is no need for such devices.
Best regards,
Rich
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