Question

When troubleshooting signal noise in a sensor circuit, why is the drain wire of a shielded cable connected to the chassis ground at only one end?

Accepted Answer

Connecting a cable shield to the chassis ground at only one end prevents the formation of a ground loop. A ground loop occurs when two points in a circuit intended to be at the same potential (zero volts) actually have a slight voltage difference between them, causing current to flow through the shield. Because a cable shield acts as a conductor, any potential difference between the ground points at the two ends of the cable will force a current to circulate through the shield wire. This circulating current creates its own magnetic field, which induces unwanted electrical noise—known as electromagnetic interference or EMI—directly into the sensitive signal wires inside the shield. By grounding the shield at only one end, you provide a path for static charges to drain to the chassis ground without completing a circuit, thus breaking the path for current to flow. This effectively blocks high-frequency interference from being captured by the shield while eliminating the risk of injecting current-based noise into your signal path.

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When troubleshooting signal noise in a sensor circuit, why is the drain wire of a shielded cable connected to the chassis ground at only one end?

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