No source or formula; just a rule of thumb: about 20,000 volts/inch for the
conditions you describe. I have run tests with 1 cm diameter stainless
steel spheres and with one sphere and one sharp hypodermic needle for an
electrode.  In air, the average breakdown was right around 20kV per inch.
With sharp points the breakdown separation is less...

As the saying goes, ymmv.

Digikey carries some and google turned up this outfit:
http://www.citelprotection.com/citel/gas_cover.htm

Hope this helps -
Tom

At 09:29 PM 4/30/2004 -0500, you wrote:
>Anyone know of a source, offhand, for spark gaps with about a 2kV limit,
or failing that, the formula for breakdown voltage in sea level normal air,
between two spheres?
>
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