How to calculate the capacitance of coaxial cable?
Coaxial Cable Capacitance Calculation Explained.
A coaxial transmission line possesses a certain capacitance per unit of length. This capacitance is defined by:
C = 24ε / log(D/d) pF/Metre
where
C is the capacitance
D is the outside conductor diameter
d is the inside conductor diameter
ε is the dielectric constant of the insulator.
A long run of coaxial cable can build up a large capacitance. For example, a common type of coax is rated at 65 pF/metre. A 150 metre roll thus has a capacitance of (65 pF/m) (150 m), or 9750 pF.
When charged with a high voltage, as is done in performing breakdown voltage tests at the factory, the cable acts like a charged high voltage capacitor.
Although rarely if ever lethal to humans, the stored voltage in new cable can deliver a nasty electrical shock and can irreparably damage electronic components.
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