4 Grounding Circuits

Basics

The primary function of a ground is safety. In electrical circuits, voltage is always measured between two points: a point of high potential and a point of low or zero potential. The voltage at the low reference point is often referred to as a “ground” or “earth ground” because it is tied directly to the earth. Grounding electrical circuits is necessary for safety in the event that a fault occurs within the system. Without a good ground, there could be potential shock hazards on any piece of electronic equipment.

You should know the following terms:

  • Chassis Ground
  • Earth Ground
  • Floating Ground
  • Ground Loop
  • Ground Noise (Hum)

Types of Grounds

In an earth ground, the term “earth” literally indicates a reference point to planet Earth. The point of contact with earth reference is generally achieved by driving a conductive spike several feet into the ground, ensuring a solid earth connection. Thus the term earth ground denotes a connection to an actual earth-based reference point as in the illustration below. 

https://en.wikipedia.org/wiki/Ground_(electricity)

The term chassis ground indicates a ground reference on a dead metal point on an electronic device. A device can have both a chassis ground (if it is grounded to a dead metal point) and an earth ground (if the device that it is grounded to is also grounded to the earth.) A good example of this is a three-prong outlet. The outlet has a ground wire in it but the wiring to the plug is also ultimately attached to the earth ground that grounds the building.  If the equipment has a chassis ground but no earth ground, it is said to have a floating ground.

In the illustration below, the 3-prong plug is grounded to the panel box and the panel box is grounded to the earth as is the transformer. 

This article provides more information about floating grounds.  

What is a ground loop?

A  ground loop occurs when two points of a circuit are intended to have the same ground reference potential but instead have a different potential between them. This is typically caused when enough current is flowing in the connection between the two ground points to produce a voltage drop and cause two points to be at different potentials. Current may be produced in a circular ground connection, otherwise known as a ground loop, by electromagnetic induction.

Ground loops are a major cause of noise, hum, and interference in audio, video, and computer systems. Wiring practices that protect against ground loops include ensuring that all vulnerable signal circuits are referenced to one point as ground. Removal of safety ground connections to equipment in an effort to eliminate ground loops also eliminates the protection the safety ground connection is intended to provide.

A ground loop typically occurs when one or more pieces of your entertainment system are plugged into the AC (alternating current) at different locations, then connected together by electrical (versus optical) signal cables—RCA, HDMI, composite, component—whose shielding is connected to ground. In the simplest terms, this creates a single-loop antenna that just loves to suck in various types of noise via electromagnetic induction.

https://en.wikipedia.org/wiki/Floating_ground#/media/File:Instruments_with_floating_ground.svg

Here are additional resources you may find useful:

Complete the following task or self-assessment:

Identify any Floating Grounds in your building(s) and correct as needed to prevent danger to students and staff.