C&D Ground

[mstrlucky74]

What's the difference between "clean" and "dirty" ground? Thanks.

 

[petersonra]

What's the difference between "clean" and "dirty" ground? Thanks.

I don't think there is any difference. people use the term "clean" and think they mean a ground free of electrical noise, and really, you might have some electrical noise on an EGC but keep in mind all the EGCs in a facility are connected together. At some point the dirty and clean grounds are tied together so it is solely a matter of degree.

 

[ron]

Depending on the context it could be the difference between a EGC and an isolated ground conductor, OR EGCs and separate supplemental grounds for a Telco or data center application (somewhat similar to an isolated ground) although all connected together at some point up stream as required by code.

 

[GoldDigger]

In terms of effect rather than mechanism, a clean ground has a low amount of stray voltage at power line frequency and above, even into the RF spectrum. It can achieve this by being well and truly grounded and bonded and by eliminating sources of current from other equipment that causes voltage on the wires both by IR drop and by electromagnetic induction and capacitive coupling.
A dirty ground is subject to unwanted voltages to remote earth caused both by other equipment and the equipment itself. These voltages can be coupled into sensitive inputs on the affected equipment, often because of poor design of signal and power ground handling in the equipment itself or attached equipment.

An alternative way to mitigate the problems purportedly caused by dirty grounds is to use differential drivers and receivers with good common mode rejection at all signal inputs and outputs and to provide isolation (as with optical couplers) that prevents unwanted currents from flowing on data ground and shield conductors.

 

[infinity]

Depending on the context it could be the difference between a EGC and an isolated ground conductor, OR EGCs and separate supplemental grounds for a Telco or data center application (somewhat similar to an isolated ground) although all connected together at some point up stream as required by code.

That would be my answer as well. Both ultimately originate at the same point but the clean ground is isolated from that point to point on the other end where it's used. The dirty ground will be connected to metal boxes, metal raceways, equipment, etc. along the way.