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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