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Equipment Grounding and Ground Loops

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Summary: Equipment Grounding

Information about grounding and tips and tricks to ensure effective grounding and equipment performance.


What is ground?


Not all grounds are the same.


  • Earth ground refers to everything connected to the metal rod hammered into the dirt outside.
    • It connects to your main breaker panel neutral bar and then to the third prong in your outlets (check your local electrical code for details).
    • It connects to all the metal surfaces (conduit, junction boxes, metal chassis) that power runs through to help ensure a breaker trips if an AC power wire shorts to the exposed metal.
    • It dissipates static charge by providing a wide area into which electric charge can spread (the dirt near your grounding rod).


  • Chassis ground is the metal equipment enclosure.
    • Usually connected to earth ground to reduce electric shock risk, though in some designs this isn't required.
    • Often connected to signal ground, but not always.


  • Signal ground refers to a common voltage reference point in a circuit.
    • All voltages are relative. 5 V means there's 5 V between point A and B. Signal ground allows you to forget about point B by assuming it's our reference point by default. Then 5 V means 5 V above ground.
    • Often marked negative or 0 V.
    • Can be connected to earth ground and chassis ground, but this is not required. A connection between signal ground and other grounds can be made directly or through an electronic filter.



Why is Earth Ground important?


  •  Your safety. Do not ground lift equipment!
    • Without a ground connection, your breakers or fuses may not protect you from electrical faults.


  • Your equipment's safety.
    • Surge protectors divert excess energy to ground during fault conditions. They may not function without a ground connection.
    • Ground dissipates static charge. Static electricity builds up on conductors. Earth ground allows that static charge to spread out into the environment, leaving your equipment.


What is a Ground Loop?

  • Ground is only supposed to form a circuit (a loop) in a fault condition in order to trip your breaker. But when you're connecting equipment together, a loop can form through the interconnect.


  • A ground loop will pick up the 50/60 Hz hum from nearby wires, and other noise, by acting as an antenna.


                                                                  A ground loop                                                                                                                                                                                                                                                    


  • Nearby high current and high voltage carrying wires will cause the most interference.


Fixing Ground Loops

  • Lift the shield at the receiver end.
    • This breaks the loop while still providing some protection from interference.


  • Make the loops smaller.
    • Put all equipment on the same circuit.
    • Some buildings have multiple grounding rods. This in combination with the long ground wires in the walls can mean creating surprisingly large antennas through the ground connection. Smaller loops will pick up less noise.
    • If equipment can't be on the same breaker, it should at least share a panel.
    • Try to imagine the path your ground wires must take.


  • Use an isolation transformer.
    • An isolation transformer breaks the ground loop while passing signals. There are a variety of manufacturers of these kinds of devices for a variety of signal types broadly under the category "hum eliminator."


  • Avoid routing signal and ground near high current and high voltage paths.
    • Although you may have taken great care to route your signal and power separately in the rack, your equipment ground wires might be right next to HVAC power or other heavy equipment power on the way to the breaker panel.


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