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# Re: Toroid Capacitance calculated without earth-distance?

```Tesla List wrote:
>
> Original Poster: "Gavin Dingley" <gavin.dingley-at-astra.ukf-dot-net>
>
> Hi Antonio,
> I have heard a rule of thumb figure of something like 10 x the radius of  the
> sphere/torroid used, in all directions.
>
> Regards,
>
> Gavin

The definition of capacitance is charged stored per unit voltage.
(C=Q/V).  The capacitance of an ISOLATED sphere, in electrostatic
units,  is exactly equal to the radius in centimeters.

In more usual units, the capacitance in uufd (pf) of an isolated sphere
is about 1.38 times the DIAMETER in inches. The capacitance of an
isolated disk is about 0.88 times the DIAMETER in inches.  The
capacitance of a toroid will be somewhere in between, depending on the
inner diameter.  The capacitance of a toroidal top load will be slightly
higher than, but probably by only a few percent.

A good article is given by  SCHOESSOW in TCBA NEWS, VOLUME 6, #2
1987.  The following table is also useful; it is based on Schoessow.
The appearance of the table depends on your terminal font, but you
should be able to edit it into readable form.

CAPACITANCE OF ISOLATED TERMINALS, DIMENSIONS IN INCHES

FROM Michael Schoessow, TCBA NEWS Volume 6, #2, 1987, pp 12-15

C, uufd, OD =	6	12	18	24	30	36

DISK	      	5.3	10.7	16.0	21.3	26.7	32.0

RING, d = 3	6.6	12.9	18.8	24.5	30.1	35.7

RING, d = 4		13.2	19.5	25.1	30.7	36.4

RING, d = 6		13.2	19.8   	25.9	31.7 	37.2

RING, d = 8	               	19.9	26.4	32.5	38.4

RING, d = 10                   	26.5 	33.0	39.2

RING, d = 12					33.1	39.6

SPHERE		8.4	16.8	25.1	33.5	41.9	50.3

C, uufd, OD = 	6	12	18	24	30	36

Ed

```