Electrical Grounding Explained | Basic Concepts

What is electrical grounding? In this article, we’re going to discuss the commonly used, but often misunderstood term, Ground. Proper electrical grounding is a critical safety measure in all electrical systems and installations.

Different names for Ground

There are lots of different names for Ground…

There’s Earth, Earth Ground, Neutral, Common Ground, Analog Ground, Digital Ground, and Instrument Ground… just to name a few. And then you have terms like Ground Loops…

What is Ground?

Ok… so… what is Ground?
That’s the big question we will answer in our discussion.

Quite often, Ground means different things to different people. For example, Ground to an electrician might mean something different than Ground to electronic engineers.

Why do we Ground?

There are lots of reasons for grounding.

Proper grounding is a critical safety measure in all electrical systems and installations.

We ground the exposed part of electrical equipment so that internal wiring failures don’t raise the voltage potential of these exposed parts to dangerous levels.

Every electrical circuit needs to be complete for the current to flow. In many applications, grounding provides a circuit return path. For example, your car chassis is a common ground for all return current to the battery.

So… let’s look at some of the different perceptions of ground.

Earth Ground

It’s probably safe to say that Earth and Earth Ground are the same things.
Earth ground is the reference point in an electrical circuit that is a direct and physical connection to… well… the earth. Earth Ground is the ground that you walk on.

Earth Ground is true zero volts. It is the true zero reference for any and every electricity discussion.

You don’t have to go far to see evidence of earth ground.
You might be able to spot a copper rod in the ground with a heavy wire attached to it.

This Earth Ground wire runs to your power panel and ultimately connects to all the Ground terminals of every receptacle in your house.

What is interesting is the fact that the Neutral terminal has a wire that ultimately connects to Earth Ground as well.

Graphical Symbol

Notice that we’ve used an electrical symbol for Earth Ground.
This symbol is probably the most misused in electrical schematics.

The symbols used to indicate ground terminals are found in the International Electrotechnical Commission document IEC 60417 Graphical Symbols for Use on Equipment.

Symbol 5017 is the symbol for Earth Ground.

Common Ground

As we said earlier, every electrical circuit needs to be complete for the current to flow. In many applications, the common ground becomes the return path. For example, your car chassis is a common ground for the return current to the battery’s negative terminal.

Sometimes you’ll see the Earth Ground symbol used incorrectly on electronic schematics. The intention is to symbolize a Common Ground and it may not be connected to Earth Ground.

Typical examples of electrical grounding

Electronic schematic

Here’s a typical example of a small part of a large electronic circuit housed in a metal chassis. There are four Ground symbols that may, or may not be connected to Earth Ground. But they are intended to indicate a Common Ground point.

We do know that if we measure the voltage from Point A to any of these common ground points we will measure +15 volts.

Ideally, the circuit would be wired like the image below with all return paths to the power supply connected at one point. Unfortunately, this is usually not practical.

If points 1 through 4 are not connected to Earth Ground but are connected to a Common Ground, it would be more appropriate to use the symbol IEC 60417 5020. This symbol suggests the points are connected to a frame or chassis terminal.

This brings up an interesting question…

Are all the components at the common ground potential connected at one point on the frame or chassis, or are they connected to the chassis at multiple locations?

Unfortunately, the schematic does not provide that answer. The schematic does not provide any clue as to physical connections. Industrial schematic drawings will indicate ground points and often provide more detail but physical connection points are still a mystery.

Industrial schematic drawings

In this example of power distribution in a Control Cabinet, there are several ground symbols. Electrically this means that all of these points are supposedly at the same voltage potential of 0V. From these drawings, we can’t determine where these grounds are connected physically in the Control Cabinet.

This brings us to a term called Ground Loops.

Ground loops

A Ground Loop is an unwanted electrical current path that can cause havoc in equipment or process control systems by introducing unwanted electrical noise.

These undesired Ground Loops are created when two supposedly connected points are not at the same electrical potential. That’s when Ohm’s Law takes over and creates an electrical current flow between these two points.

In our example, Ground loops can be avoided if all three devices are grounded together at one point. This type of grounded is referred to as Star Point grounding.

Unfortunately, in large industrial plants, multiple-point grounding is the reality, and the possibility of ground loops is high.

With so many connections referenced to the ground within a facility, the chances of needing more than one ground point are great.

Summary

Ok… let’s review…

– Quite often, Ground means different things to different people.
Proper grounding is a critical safety measure in all electrical systems and installations.

– In many applications, grounding provides a circuit return path.
Earth Ground is true zero volts. It is the true zero reference for any and every electricity discussion.

– Earth ground is the reference point in an electrical circuit that is a direct and physical connection to the earth.

– A Ground Loop is an unwanted electrical current path that can cause havoc in equipment or process control systems by introducing unwanted electrical noise.

– Ground Loops are created when two supposedly connected points are not at the same electrical potential.

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