In this video, we're going to discuss the commonly used,
but often misunderstood term, 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 …
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.
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 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.
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.
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.
As we said earlier,
every electrical circuit needs to be complete for 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.
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 this
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.
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.
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 ground within a facility,
the chances of needing more than one ground point are great.
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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