# Re: "human" topload

• To: tesla-at-pupman-dot-com
• Subject: Re: "human" topload
• From: Terry Fritz <twftesla-at-uswest-dot-net>
• Date: Sun, 10 Sep 2000 19:36:45 -0600
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

```Hi Jim,

At 01:59 PM 9/7/00 -0700, Jim Lux wrote:
snip...
>For what it's worth, a sphere 1 meter radius in free space has a capacitance
>of about 110 pF.  If it is close (within 5 radii) of a grounded surface, the
>C is going to rise.  The mathematically inclined (and masochistic) can do
>this by considering the ground as a reflector and calculating the
>capacitance between two spheres separated by 2d, where d is the distance to
>ground.  This in itself is non trivial (there isn't a closed form solution).
snip...

Actually, a single graph would do it all.  The only defining aspect to the
capacitance of a sphere above an infinite plane is the diameter to distance
factor.  So if you knew the capacitance of a 1 meter ball 1 meter above a
plane, the capacitance if a 1/2 meter ball 1/2 meter above the plane would
simply be 1/2 of the 1 meter ball's capacitance.  A chart with a normalized
1 meter ball's capacitance vs. distance above the plane could be used for
any diameter sphere just by multiplying the capacitance by the diameter
factor.  A toroid is a bit different, but the answers would probably still
be close.

The terminals we use are far enough above ground that this effect would
probably not be significant.  E-Tesla5 does this stuff already taking into
account the other TC variables, so the generation of such a chart would
probably not be useful to us...

Cheers,

Terry

```