Ground loop (electricity)From Wikipedia, the free encyclopedia

In an electrical system, a ground loop is an unwanted current in a conductor connecting two points that are supposed to be at the same potential, often ground, but are actually at different potentials.

Ground loops are a major cause of noise, hum, and interference in audio, video, and computer systems. They can also create an electric shock hazard, since ostensibly "grounded" parts of the equipment, which are often accessible to users, are not at ground potential.

Contents

1 Description■2 How it works■3 Common ground loops ■

3.1 Ground currents on signal cables■3.2 Sources of ground current■3.3 Solutions■3.4 Balanced lines■

4 In circuit design■5 See also■6 References■7 External links■

Description

A ground loop in a system causes circuits designed to be at the same potential to be at different potentials. Ground loops can be hazardous, or cause problems with the electrical system, because the electrical potential and soil resistance at different points on the surface of the earth can vary.

In a floating ground system, that is, one not connected to earth, the voltages may be unstable, and if some of the conductors that constitute the return circuit to the source have a relatively high resistance, or have high currents through them that produce a significant voltage drop, they can be hazardous.

Low-current wiring is particularly susceptible to ground loops. If two pieces of audio equipment are plugged into different power outlets, there will often be a difference in their respective ground potentials. If a signal is passed from one to the other via an audio connection with the ground wire intact, this potential difference causes a spurious current through the cables, creating an audible buzz at the AC mains base frequency (50 or 60 Hz) and the harmonics thereof (120 Hz, 240 Hz, and so on), called mains hum.

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