Ground loop (electricity)
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In an electrical system, ground loop refers to a current, generally unwanted, in a conductor connecting two points that are supposed to be at the same potential, that is, ground, but are actually at different potentials. Ground loops can be detrimental to the intended operation of the electrical system.
Description
A ground loop in a medium connecting circuits designed to be at the same potential but at different potentials can be injurious to the electrical system. For example, the electrical potential at different points on the surface of the Earth can vary by hundreds of volts, primarily from the influence of the solar wind. Such an occurrence can be hazardous, for example, to personnel working on long, grounded conductors such as metallic telecommunications cable pairs.A ground loop can also exist in a floating ground system, that is, one not connected to an Earth ground, if the conductors that constitute the ground system have a relatively high resistance, or have, flowing through them, high currents that produce a significant voltage (I·R) drop.
Audio 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 unbalanced connection, this potential difference causes a spurious current to flow through the cables, creating an audible buzz at the AC mains frequency (50 or 60 Hz) and the harmonics thereof (120 Hz, 240 Hz, and so on). Sometimes, performers remove the grounding pin from the electrical wiring to avoid ground loops, however, this creates an electrocution risk; the correct solution is to use isolation transformers, opto-isolators or baluns to avoid a direct electrical connection between the different grounds.
In video, ground loop can be seen as hum bars (bands of slightly different brightness) scrolling vertically up the screen. These are frequently seen with Video projectors where the display device has its case grounded via a 3-prong plug, and the other components have a floating ground connected to the Cable television coax. In this case the video cable is grounded at the projector end to the home electrical system, and at the other end to the cable TV's ground, inducing a current through the cable which distorts the picture. As with audio ground loops, this problem can be solved by placing an isolation transformer on the cable-tv coax. Alternatively, one can use a surge protector that includes coax protection. If the cable is routed through the same surge protector as the 3-prong device, both will be regrounded to the surge protector.
See also
External links
Audio equipment
- [Sound System Interconnection] — from Rane Corporation
- [Grounding and Shielding Audio Devices] — from Rane Corporation
- [How to test for the pin-1 problem]
- [Equipment Wiring: Internal to Electronic Equipment]
- [Signal purity]
- [Bonding Cable Shields at Both Ends to Reduce Noise]
- [Build a "hummer" to find "pin-1" ground problems]
- [An Easily Implemented Procedure for Identifying Potential Electromagnetic Compatibility Problems in New Equipment and Existing Systems-The Hummer Test] — Available for purchase
- [Noise Susceptibility in Analog and Digital Signal Processing Systems] — Available for purchase
Video equipment
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