Spark gaps were mentioned in a previous entry (in the old project page) at 4. Spark gaps

Spark gaps are a "free" but lousy solution that have bad repeatability and low reliability. They work above some kV, which makes them hardly useful in common situations (like a spike above 400V when a lousy device like an electric drill or a vacuum cleaner is working from the mains)

While looking for other parts, I found a box of EPCOS surge arrestors that I had totally forgotten (leftover from another project). They are rated at 350V and are welcome because the PSU modules have no MOV or other protection device, not even a series fuse/resistor.

I usually add MOVs to the electrical box, just in case. Now I imagine that my board can also serve as an additional protection to the connected circuits...

How can I test my PSU and device for high-voltages peaks ? I don't have the suitable testing devices...