Definition of a 'Clean Earth'

[SimpleSimon]

Who would like to give their definition of a 'clean earth' when being used with IT/data equipment? My understanding would be an earth that goes back to the Original MET of the buildings incomer, by-passing any earthing terminals found in sub-boards?

Here's my scenario-
Condition Report on a large shop floor last night. One sub board identifies Tills marked as 'Clean Tills' and one marked 'Dirty Tills'. So an educated guess (and the other Spark with me who has been on site previous telling me it means clean earth) has bought me here. But the earth is exactly like the ones for the 'dirty tills', terminated in the same Sub-board earth terminal. I than begin thinking, maybe it is a high integrity earth for the socket outlets, but they are run in radials without the earth run in a ring?? They are also not terminated in seperate CPC terminals behinf the socket outlets. And no mention of any high integrity earth on the board either.
So Ive coded C3 further investigation, my plan is to use an earth leakage clamp, take a reading of the clean tills. If over 10mA than suggest circuit have its earth run as a ring.
If under 10mA, than I'll just readjust the wording of the circuit decription.:biggrin5:

 

[i=p/u]

i believe its in the form of a ring making it a functional earth...

 

[spark 68]

I have built switchgear before utilising a 'clean Earth', this Earthing bar was seperate and insulated from the protective earthing bar, with only the clean circuits (all RCBO's) terminated on this bar.

Now obviously from the scenario above I only had the specs for this part of the project, and not the full picture so to speak, but speaking to the clients engineer I was led to believe that this bar was going on a seperate Earthing system (TT, I believe) whilst the main board was a TN system.

I understand there is more than one way of doing things, and this may not be correct for all circumstances.

 

[SimpleSimon]

I have built switchgear before utilising a 'clean Earth', this Earthing bar was seperate and insulated from the protective earthing bar, with only the clean circuits (all RCBO's) terminated on this bar.

Now obviously from the scenario above I only had the specs for this part of the project, and not the full picture so to speak, but speaking to the clients engineer I was led to believe that this bar was going on a seperate Earthing system (TT, I believe) whilst the main board was a TN system.

I understand there is more than one way of doing things, and this may not be correct for all circumstances.

Something like this scenario is what I was expecting. A seperate earth bar but can't see anything like it.

 

[Darkwood]

Its unlikely you have ever come across a clean earth situe' to start with if the earth is round then its unlikely to be able to do its job.... check this link out and as cocky as hes trying to be its also informative..
Marc's Technical Pages: Power Quality Symptoms and Solutions - The Clean Earth Conspiracy

 

[spark 68]

Maybe independent Earth is a better term then.

 

[i=p/u]

filters could make it clean earth, like in a fish tank

 

[Chr!s]

Or Quiet Earth

 

[Darkwood]

I have built switchgear before utilising a 'clean Earth', this Earthing bar was seperate and insulated from the protective earthing bar, with only the clean circuits (all RCBO's) terminated on this bar.

Now obviously from the scenario above I only had the specs for this part of the project, and not the full picture so to speak, but speaking to the clients engineer I was led to believe that this bar was going on a seperate Earthing system (TT, I believe) whilst the main board was a TN system.

I understand there is more than one way of doing things, and this may not be correct for all circumstances.

I see what your saying here but having a totally seperate earthing system like this could create large potential differences between the 2 earthing systems fed from the same supply line, an uneasy feeling goes through me at the thought of such a system, there is another way to create an independant clean earth and that would be to get a delta to star transformer and create a N/E center tap point thus creating an isolated independant earthing system originating from the same incoming supply.

 

[spark 68]

Hi Darkwood,

The switchgear were PDU's, (for computer/data systems), and like I say I only had part of the information, the main part I was referring to was the fact that the 'independent earths' were physically and electrically seperate at the distribution level at least.

As I said in my earlier post, there is more than one way to achieve the same results.

 

[Darkwood]

Hi Darkwood,

The switchgear were PDU's, (for computer/data systems), and like I say I only had part of the information, the main part I was referring to was the fact that the 'independent earths' were physically and electrically seperate at the distribution level at least.

As I said in my earlier post, there is more than one way to achieve the same results.

Arrh yes see your angle now, just got mis-directed but yes agree its a confusing terminology using the term clean earth as it rarely is and clashes with other industries and their use of the term, no doubt it will be another 70quid to buy a next edition regs just for this issue :thumbs_down:

 

[MarkieSparkie]

May be nothing to do with earthing arrangements. One set of tills for the clean money and one set of tills for the dirty money (to be laundered later).:jester:

 

[Engineer54]

For IT buildings of any size, that are primarily for Data processing and the like the so-called clean earth would be derived from it's own TT earth field. Clean earth may not be a particually good name for such an earthing system, but what it means basically is that there are no, or very little dirty noise on the system from other sources. Of course when all this IT equipment is connected it will be creating it's own leakage, but should and will not be subject to all the dirty type of noise that is associated with, and most certainly will be present on a general service earth system, whether run isolated directly from the MET, or not!!...

As others have stated there are more than just the one way to achieve similar results!!

Anyway the above is basically what i would call a clean earth system, others may well call it something else... To me it's just an earthing system, that's free from outside potential harmful influences...

 

[SimpleSimon]

For IT buildings of any size, that are primarily for Data processing and the like the so-called clean earth would be derived from it's own TT earth field. Clean earth may not be a particually good name for such an earthing system, but what it means basically is that there are no, or very little dirty noise on the system from other sources. Of course when all this IT equipment is connected it will be creating it's own leakage, but should and will not be subject to all the dirty type of noise that is associated with, and most certainly will be present on a general service earth system, whether run isolated directly from the MET, or not!!...

As others have stated there are more than just the one way to achieve similar results!!

Anyway the above is basically what i would call a clean earth system, others may well call it something else... To me it's just an earthing system, that's free from outside potential harmful influences...

Thanks 54. Pretty much what i thought and pretty much whats NOT in place.

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