TN-C-S and an Earth Rod?

[bernardgreen]

Another form of "bonding" but at several thousand volts above Earth potential

 

[JohnW2]

No they are not John, you are correct.

Thanks for confirming. It's nice to get something right

Earthing is what we do at the supply, whether from the supplier or own earth rod/plate et etc and it relies on the Earthing principle. Bonding is what we do to join things together to equalise the potential.

Indeed so.

Main Bonding we , not long ago, named EEBADS or Earthed Equipotential Bonding Disconnection of Supply.

I think that it actually stood for "Earthed Equipotential Bonding AND Automatic Disconnection of Supply", the 'bonding' and the ADS being two totally separate/different things - so I don't think it is true to say that Main Bonding was "named" EEBADS".

We were told there is no such term as "Earth Bonding" but I do not quite agree with that in reference to main bonding.

In order to create an equipotential zone and therefore theoretically remove risk of electric shock when someone touches two things within the building, the Main Bonding theoretically does not need to be 'earthed' (although, in reality, it always will be). However, if one wants ADS to disconnect the supply in the event of an 'L-E' (usually L-CPC' fault), it is essentially that exposed-c-ps are not only all 'equipotential', but also that they have a low impedance path to hearth (hence to the neutral at DNO's transformer).

If we have two or more "Earth Sources" in a supply they must be joined together - ...

Sure - as is true of any extraneous-c-ps which enter the property, whether they be thought of as 'earths' or not.

So if you have an Earth Rod etc you must robustly join it to your Main Earth

Indeed -f a connection to it enters the property, that represents an extraneous-c-p which needs to be Main Bonded.

(System earth if you like), ...

For what it's worth I personally do not particularly "like" - I find this distinction between "System" and "Equipment" earths to be more confusing (and, as I've said, potentially misleading, unless you count human beings as 'equipment' ) than helpful .... but maybe that's just me !

Kind Regards, John

 

[EFLImpudence]

Indeed -f a connection to it enters the property, that represents an extraneous-c-p which needs to be Main Bonded.

Mmmmm. Where would that "connection" be going if not to the MET - therefore would it not BE the Main Bonding?

Would it not be just as well to remove that "connection" so as to render the rod's "connection" not an extraneous-c-p but just another isolated piece of metal in the garden?

(I realise there are plans afoot to require an earth rod in addition to the supplier's earth but until then...)

 

[ebee]

I think that it actually stood for "Earthed Equipotential Bonding AND Automatic Disconnection of Supply", the 'bonding' and the ADS being two totally separate/different things - so I don't think it is true to say that Main Bonding was "named" EEBADS".

Yep, my bad on that one, you are quite correct, in fact it was sometimes named EEBADOS too. LOL

 

[ebee]

I find this distinction between "System" and "Equipment" earths to

No I said System Earth to mean the Suppliers facility and/or Earth Electrode. I did not intend to infer as opposed to "Equipment Earth" as such, more like everything else or much of it.

 

[JohnW2]

Mmmmm. Where would that "connection" be going if not to the MET - therefore would it not BE the Main Bonding?

If a connection from the rod goes to the MET, then that is the #'Main Bonding satisfied. If a cable connected to the earth rod simply enters the property by 'goes nowhere', but with a 'touchable end' (not uncommon when TT has been changed to TN), then it would be an extraneous-c-p which needed to be connected ('bonded') to the MET. That was my point - that, if the cable enters the property it must be connected to the MET, whether yiou choose to call that 'bonding'or not.

Would it not be just as well to remove that "connection" so as to render the rod's "connection" not an extraneous-c-p but just another isolated piece of metal in the garden?

Sure - but, as above, if a conductor connected to that bit of metal in the garden enters the property, it needs to be treated as an extraneous-c-p.

I suppose my main point is to remind folk that an 'earth rod' is merely one example of an extraneous-c-p - which meant that it made no sense that some people got concerned when BS7671 'nearly' required earth rods in all TN installations!

(I realise there are plans afoot to require an earth rod in addition to the supplier's earth but until then...)

As above, when it happens (I suspect in the next ed of BS7671, there will be no real reason for any concerns, since many/most installations have bonded extraneous-c-ps already!

 

[JohnW2]

No I said System Earth to mean the Suppliers facility and/or Earth Electrode. I did not intend to infer as opposed to "Equipment Earth" as such, more like everything else or much of it.

In that case, I think that you're confusing things even more, by using "System Earth" to mean something different than has been suggested

Kind REgards, John

 

[EFLImpudence]

I suppose my main point is to remind folk that an 'earth rod' is merely one example of an extraneous-c-p -

Not if it is outside.

That is what seemed odd about what you wrote.
Why would a "connection" - presumably a conductor - be regarded as an extraneous-c-p?
It would either BE the main bonding conductor (what else could it be?) or could be removed; thus removing the extraneous-c-p.

which meant that it made no sense that some people got concerned when BS7671 'nearly' required earth rods in all TN installations!

Well - unless they don't have one now and have to pay for something else now deemed essential.

 

[ericmark]

I do fancy getting a picture of a bag Fullers earth with an earth rod in it. The running out of the leads for testing earth rods was a pain, how can one put the test probes in 25 yards away on a tarmac drive or road?

Once there is a supply, one can compare to the DNO earth, it will show higher than it really is, but at least you know it is good enough.

 

[JohnW2]

Well - unless they don't have one now and have to pay for something else now deemed essential.

I was talking about the electrical concerns ('dangers') that some expressed, not financial ones.

If I recall, I think some even went as far as saying that one "MUST NOT" connect a local earth electrode to a TN installation's 'earth' ('because that would be dangerous') - but I presume the same people were happy to (as 'required') connect any other extraneous-c-p to a TN MET (because it was then called 'bonding')

 

[ebee]

I have seen some installations with substandard main bonding and the "Electricians" have deliberately

but I presume the same people were happy to (as 'required') connect any other extraneous-c-p to a TN MET (because it was then called 'bonding')

yes I know LOL

 

[ebee]

In that case, I think that you're confusing things even more, by using "System Earth" to mean something different than has been suggested

Go on the, I did not see the you tube video before commenting (remiss of me I lknow).
What was meant by "System Earth" I meant the MET as we use from our supply, OK the Installation Earth as used at the MET- the BIg One I suppose, the defining Earth of our Electrical Installation

 

[JohnW2]

Go on the, I did not see the you tube video before commenting (remiss of me I lknow).

Nor had I - but reading Frodo's post was enough to tell me that "System Earthing" (or "System Grounding") was being used in a sense that I would never have imagined, and nor a sense in which I can recall having seen/heard it used in the UK.

What was meant by "System Earth" I meant the MET as we use from our supply, OK the Installation Earth as used at the MET- the BIg One I suppose, the defining Earth of our Electrical Installation

Exactly. If I were to use the term "System Earth" (which I doubt I would) I would be referring to "the 'earth' of the system (aka Installation, aka the MET).

Kind Regards, John