# Re: Minimum distance

Original poster: Mddeming@xxxxxxx I thought that the original question had to do not with flashover distance but rather with what effect the proximity of the mass of the transformer had on the coupling and tuning of a coil. Perhaps I misunderstood.

Matt D.

In a message dated 8/23/06 2:11:37 P.M. Eastern Daylight Time, tesla@xxxxxxxxxx writes:
Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>

Hi Ben, all,

A 10 kV/inch rule of thumb should prevent almost any
flashover danger, at least at 60 Hz or DC, as you say.
However, there are a number variables when determining
the breakdown distance vs voltage, such as atmospheric
conditions (temperature, humidity, barometric pressure)
and the physical size and geometry of the electrodes.
This makes an "ironclad" voltage/spark length graph all
but impossible. I think the theoretical maximum voltage standoff that
1" of air can withstand is 76 kV, but of course that's with smooth
spherical electrodes of at least the dia-
meter of the spark gap distance itself. Any deviation from this
"controled" laboratory spark gap setup will result in a much lower
kV/inch rating. I've heard that with needle
point electrodes, the kV/inch is somewhere between 15
kV and 25 kV(DC). And of course, with high frequency AC, all bets are
off as the voltage/spark length ratio goes
down significantly with a subsequent increase in frequency. Also,
remember that a 60 Hz AC rms voltage  reading must be multiplied by
1.4 to determine the true sine wave peak
voltage.

David Rieben