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Collaboration, Voice & AV · Intermediate

Ground Loop

An unwanted current path formed when equipment is grounded at multiple points with different potentials, causing hum.

Definition

Ground loops produce 50 or 60 Hz hum and buzz on audio and rolling bars on analog video. Remedies include proper single-point grounding, balanced interconnects, isolation transformers and ground lift switches on signal shields. Safety ground on power cords must never be removed.

Example

A projector and an audio rack on different electrical panels create hum, cured with an audio isolation transformer.

Exam tip

Never lift safety ground; break the loop on the signal path instead.

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