Difference between earth, chassis, and power supply grounds

[Involute]

This would be a great topic for Fundamentals Friday (if it's not too basic).

[TVman]

I "think" it's all the same.

[Monkeh]

I "think" it's all the same.

It really isn't.

Ground is not ground, and it's certainly not earth.

[SeanB]

Earth ground - The connection that goes to the power line earth, that eventually goes to a spike or earth mat that is in the outside earth, used mostly to dissipate static charge.

Chassis ground - The connection to the metal chassis the unit is supported on. It may be floating from earth ground or connected to it, or even to one side of the mains.

Power supply ground - The current return path for the power supply. It may be connected to the chassis or not.

Thus you can have a power supply ground that is isolated from the chassis ground, while the chassis ground is sitting at 300V from a mains bridge rectifier, and the metal parts of the case that you can touch are connected to earth ground.

[TVman]

Earth ground - The connection that goes to the power line earth, that eventually goes to a spike or earth mat that is in the outside earth, used mostly to dissipate static charge.

Chassis ground - The connection to the metal chassis the unit is supported on. It may be floating from earth ground or connected to it, or even to one side of the mains.

Power supply ground - The current return path for the power supply. It may be connected to the chassis or not.

Thus you can have a power supply ground that is isolated from the chassis ground, while the chassis ground is sitting at 300V from a mains bridge rectifier, and the metal parts of the case that you can touch are connected to earth ground.

I just learned something, Thank you!

[Neilm]

Earth ground - The connection that goes to the power line earth, that eventually goes to a spike or earth mat that is in the outside earth, used mostly to dissipate static charge.

This is the one used for safety return on mains powered equipment

[AG6QR]

One more point about earth ground:  The earth isn't always a great conductor, so two stakes hammered into the ground at different places, even relatively close together, aren't always at the same potential.  This can be especially true if lighting is in the process of striking the ground close by.

Electrical codes may vary from one region to another, but the ones I'm familiar with require an earth ground at the point where utility service enters a building.  Some radio antennas also require an earth ground, and if you have antennas on towers, it's common to require that the tower have an earth ground for lightning protection.  These ground points may or may not be right near the utility service entrance.  For safety's sake in case of lightning strike, if you have more than one stake pounded into the earth, it's important that all such stakes be bonded together with a conductor with very high current capacity.  If there's going to be a potential difference between different earth ground stakes, don't force the potential difference to go through any radios or other delicate equipment.  It's not a good idea to have the shield of a radio's antenna connector going to one earth ground by the antenna tower, while its chassis is connected to a different earth ground next to the utility service entrance.

[Monkeh]

One more point about earth ground:  The earth isn't always a great conductor, so two stakes hammered into the ground at different places, even relatively close together, aren't always at the same potential.  This can be especially true if lighting is in the process of striking the ground close by.

This is why ground isn't ground and isn't earth, either.

[miguelvp]

Simple:

Earth:


Chassis:


Power Supply Grounds:

[Dave Turner]

Used to have the return (ground) for our telephone provided by a copper spike driven into the ground. In dry weather we could improve reception/transmission by pouring water over the spike. Think about it!

[VEGETA]

yes! i do aid such a topic!

[nixfu]

Most of this confusion comes into play when you have AC vs DC or you have both in your device.  There are important differences to keep in mind when you work with them. 


Dave did touch on this in "how to keep from blowing up your scope", but more could maybe help with maybe a video of "how to keep from blowing up YOURSELF and your project". 

[tggzzz]

Earth ground - The connection that goes to the power line earth, that eventually goes to a spike or earth mat that is in the outside earth, used mostly to dissipate static charge.

Chassis ground - The connection to the metal chassis the unit is supported on. It may be floating from earth ground or connected to it, or even to one side of the mains.

Power supply ground - The current return path for the power supply. It may be connected to the chassis or not.

Thus you can have a power supply ground that is isolated from the chassis ground, while the chassis ground is sitting at 300V from a mains bridge rectifier, and the metal parts of the case that you can touch are connected to earth ground.

You might like to add: PCB/circuit ground -a fiction, especially when considering RF. Suc a "ground" can act as an excellent antenna and/or part of the passive circuit elements that determine the circuit's operation.

[janoc]

Most of this confusion comes into play when you have AC vs DC or you have both in your device.  There are important differences to keep in mind when you work with them. 

It is enough to work with most commercially made lab power supplies. You get a black terminal (ground) and a green one (mains earth, most often chassis connected). They are often bridged by a slab of metal between the binding posts, but sometimes they are not (floating PSU).

And yeah, it is important to be aware of the difference, because having non-floating connections is a good way to blow up your instruments (by shorting through the common mains earth wire).

[robrenz]

Practical Electronics for Inventors has quite an extensive section on this topic.

[LabSpokane]

When in doubt, ohm it out.

[gilbenl]

+1 for this suggestion. Maybe some practical considerations as well when designing circuits as well.