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Capacitor Specifications

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The specifications for a capacitor usually include the value of capacitance (expressed in μF, nF, or pF), the voltage rating (i.e. the maximum voltage which can be continuously applied to the capacitor under a given set of conditions), and the accuracy or tolerance (quoted as the maximum permissible percentage deviation from the marked value).

Other practical considerations when selecting capacitors for use in a particular application include temperature coefficient, leakage current, stability and ambient temperature range.

Tolerance

Due to manufacturing tolerances, a capacitor marked with a value of 100nF will not usually have a value of precisely 100nF. For example, a capacitor marked 100nF and produced with a tolerance of ±10% will have a value which falls within the range 90nF to 110nF.

Capacitors are usually produced with tolerances of ±5%, ±10% or ±20% but the tolerance rating is often not marked on the body of the capacitor.

Voltage rating

All capacitors have a maximum voltage rating which specifies the maximum continuous potential difference that can be safely applied to the component. Exceeding this rating can have serious consequences as the dielectric material (e.g. plastic or ceramic material) can break down and become permanently conductive. Typical voltage ratings are 50V, 100V, 250V, 400V and 1kV (but note that different voltage ratings may apply for a.c. and d.c. working).

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