- Ground loops DATA SHEET

Ground loop problems and how to get rid of them

Written and copyright by Tomi Engdahl 1997-1999.

Why grounding is so important ?

Improper grounding can create a lethal hazard. Correct grounding is essential for correct operation nad safety of electrical equipments. Grounding can solve many problems, but it can also cause new ones. One of the most common problem is called "ground loop".

Why ground loop is a problem ?

Ground loops are a mystery to many people. Even college-trained electronic engineers may not know what ground loops actually are. Engineers have either concentrated on power distribution (for the electric company) or on equipment that happens to plug in to the power distribution system. Not much thought has been given to power distribution and equipment as a single entity where ground loops arise.

Ground loops are the most common cause of AC line frequency hum in sound systems. A ground loop in the power or video signal occurs when some components in the same system are receiving its power from a different ground than other components, or the ground potential between two pieces of equipment is not identical.

Ground loop is a common problem when connecting multiple audio-visual system components together, there is a good change of making a nasty ground loops. Ground loops commonly cause humming noise to audio signals and interference bars to picture. Ground loop makes the system sensitive to pick up interference from mains wiring which can lead to erratic operation of the quipments or even damages to the equipments. Audio-frequency groundloop problems are typically in the low millivolt range, so it does not have to be much interference in grounding system to cause problems in audio systems.

Remeber that there is no absolute ground. There is a certain amount of resistance to electrical current between all grounding points. This resistance can change with humidity, temperature, connected equipment and many other variables. No matter how small, the resistance can always allow an electrical voltage to exist across it. The ground wires between wall sockets and power company transformers are not perfect conductors and neither is the shield of your coaxial video cable. If they were, ground loops would not be a problem.

General topics

• Why grounding is used in electrical wiring
• Basics of groundloops
• Electrical wiring in buildings
• Examples of different AV system with and without ground loop problems
• How the signal cable grounding is done in typical AV equipments
• Mains connectors
• Naming Electricity System Earthing Arrangements
• Solving typical home AV system ground loop problems
• Other than ground loop related sources of humming
• Why do you have to use a separated conductor for grounding and for neutral?

Home audio and video systems

• Audio signal grounding in audio equipments
• Solving AV problems in typical home system

Professional audio systems

• Advice on setting up hum free safe PA system
• Balanced power systems
• How to correctly wire audio equipment racks
• Methods for breaking ground loop
• Reducing microphone hum
• Wiring audio equipment racks and studio
• Ground lift circuits
• Audio isolation circuits and how to build your own
• Digital audio and groundloops

Professional video systems

• Ground loops in video systems
• Antenna cable isolators and how to build your own

Data networks

• What causes computer problems
• Datacom isolation
• Mains isolation possibilities - and why does it not help always

Laboratory environment

• Mains isolation possibilities

Design tips

• Design tips for balanced audio connections
• Ground loops inside circuits

  Further info from Tomi Engdahl's site at http://www.epanorama.net

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