Meaning of Black Stripe on Non-Polarized Capacitors—Does It Indicate Polarity?

The black stripe on one end of certain non-polarized capacitors, particularly older types like paper and some polystyrene capacitors, indicates the connection to the outer foil. This marking designates the end that should be connected to the lowest AC potential, often ground, to provide partial self-shielding and reduce electrical interference. For example, in low pass filter applications, the striped end is best connected to ground to shield the signal from noise. In high pass filters where neither side is grounded, connecting the stripe to the low impedance side helps minimize susceptibility to noise. These older paper capacitors are typically over 50 years old and prone to leakage after long service, unlike more modern capacitors such as certain red capacitors which do not exhibit this leakage. The stripe does not indicate polarity in the conventional sense but serves as a guide for optimal electrical performance and noise reduction.
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