Re: Carriage bolt spark gap equation

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

> In the course of hi-pot testing some capacitors, I also took the
> opportunity to measure the DC breakover potential for
> the 1/4" thread carriage bolt safety gaps which protect the capacitors.  I
> used a hi-pot testing station which generates
> DC voltages to 35kV.  Over the range of 4500V to 20,000V, the relationship
> of gap spacing to voltage was very linear.
>
> The equation I derived from the data is:
>
>  gap spacing (inches) = 1.338 V + 0.0257, for Voltages from 4500V to
20,000V
>
>
> Perhaps this equation will prove useful for those who use these types of
> carriage bolts for building safety gaps and the
> like.
>
> Aric

Only for absolutely identical carriage bolts (same head size / radius
etc...)  Also, did you ensure that your carriage bolt heads were
COMPLETELY smooth and free from dirt, dust, and anything else.

A single piece of dust is enough to initiate a big arc at a lower voltage
compared to the rather large radius surface of your carriage bolt.

I did the same experiment awhile back using 3/8" corona balls for electrodes
and again using 1/2" corona balls.  There was considerable
difference in the measurements for arc-overs vs. distance measurements.

I think if you did the same experiement using a slightly larger or slightly
smaller carraige bolt, your formula would be different.

Dan