Earth bonding regulations

[JohnW2]

Yes two separate dwelling each with their own electric installation. Basement = flat 2 floors above = maisonette

In that case, there could well be some 'discussion' about (real) main bonding requirements. Some will say that the gas and water pipes should be bonded to the 'MET' of the electrical installation of the corresponding dwelling at the point that the pipes enter that dwelling.

View media item 84049

Am I right in saying that those five pipes are connected to each other, but not to any electrical earth (at CU or wherever)? If so, that is the usual (unnecessary) format of "plumbers cross-bonding"

Kind Regards, John

 

[HawkEye244]

Yes two separate dwelling each with their own electric installation. Basement = flat 2 floors above = maisonette

In that case, there could well be some 'discussion' about (real) main bonding requirements. Some will say that the gas and water pipes should be bonded to the 'MET' of the electrical installation of the corresponding dwelling at the point that the pipes enter that dwelling.

View media item 84049

Am I right in saying that those five pipes are connected to each other, but not to any electrical earth (at CU or wherever)? If so, that is the usual (unnecessary) format of "plumbers cross-bonding"

Kind Regards, John

Ah ok, well if someone is adamant on here that I need to change the earth to go to the corresponding CU that's won't be a great stretch to do, walls and cable has already been run, would just need a longer cable ( CU's are few meters apart as it happen) - I won't bother if it's not strictly necessary on H&S/ regulation grounds.

Your last question about the pipes - they join to one another but you see the last vertical pipe on the right? the cable there is clipped to the copper and then runs all the way to the CU, it's difficult to make out in the picture =)

 

[JohnW2]

Ah ok, well if someone is adamant on here that I need to change the earth to go to the corresponding CU that's won't be a great stretch to do, walls and cable has already been run, would just need a longer cable ( CU's are few meters apart as it happen) - I won't bother if it's not strictly necessary on H&S/ regulation grounds.

Unfortunately for you, you're more like to see 'a debate' as any 'adamance' (is there such a word?!). It may not only be a question of which CU to bonding cables go to - since, as I said, some people will probably say that the bonding connection to the pipes should be close to where those pipes enter the particular dwelling. Let's see what others say!

Your last question about the pipes - they join to one another but you see the last vertical pipe on the right? the cable there is clipped to the copper and then runs all the way to the CU, it's difficult to make out in the picture =)

OK. Yes, now you mention that, I can just about see it in the picture. That's a bit more than plumber's often/usually do, then!

Kind Regards, John

 

[EFLImpudence]

The Main Bonding should be from the point of entry to the building to the Main Earthing Terminal of the entire installation.

If there are separate dwellings then each dwelling should be treated the same.
I.e. from point of entry to the dwelling to its Earth Marshalling Terminal - which strictly speaking is not a MET.

 

[JohnW2]

The Main Bonding should be from the point of entry to the building to the Main Earthing Terminal of the entire installation. If there are separate dwellings then each dwelling should be treated the same. I.e. from point of entry to the dwelling to its Earth Marshalling Terminal - which strictly speaking is not a MET.

Fair enough - but have we established whether there is "one ('entire') electrical installation" or two (all we seem to know is that there are two meters and two CUs)?

Kind Regards, John

 

[EFLImpudence]

Fair enough - but have we established whether there is "one ('entire') electrical installation" or two (all we seem to know is that there are two meters and two CUs)?

Perhaps we haven't but if each dwelling is connected as I have said then it doesn't really matter as it will be correct and is, I would think, the reason for so doing it.

Plus - there may be one electrical installation yet separate gas.

 

[JohnW2]

Fair enough - but have we established whether there is "one ('entire') electrical installation" or two (all we seem to know is that there are two meters and two CUs)?

Perhaps we haven't but if each dwelling is connected as I have said then it doesn't really matter as it will be correct and is, I would think, the reason for so doing it. Plus - there may be one electrical installation yet separate gas.

OK - so, if I may, to get this clear in my mind ... you are saying that each service should be bonded from where it enters each dwelling to the local earth point of that dwelling (Earth Marshalling Terminal). Is that (which is what I suggested to OP, other than calling the local earthing point a 'MET') correct? I would imagine that with setups like the OPs, entry of a service into one of the dwellings will also correspond to entry into the building, so does the bonding of that to that dwelling's 'earthing point' make that a MET (for the entire installation) as well as an Earth Marshalling Point for the individual dwelling? If the service does not enter the building into one of the dwellings (but, instead, into some 'common area'), do I take it that it then has to be bonded to a MET, close to the origin of the installation, in addition to the bonding (to local Marshalling Point) in each of the dwellings?

Kind Regards, John

 

[EFLImpudence]

OK - so, if I may, to get this clear in my mind ... you are saying that each service should be bonded from where it enters each dwelling to the local earth point of that dwelling (Earth Marshalling Terminal).

Yeeeessss.

Is that (which is what I suggested to OP, other than calling the local earthing point a 'MET') correct?

Yes. (I think so without reading it again)

I would imagine that with setups like the OPs, entry of a service into one of the dwellings will also correspond to entry into the building,

I would think so for the electric and water but as I pointed out the gas may be external and separate

so does the bonding of that to that dwelling's 'earthing point' make that a MET (for the entire installation) as well as an Earth Marshalling Point for the individual dwelling?

For the first one (ground floor) it probably does.
In larger blocks it will likely be in a separate room where will be THE MET and each dwelling will be an EMT.

If the service does not enter the building into one of the dwellings (but, instead, into some 'common area'), do I take it that it then has to be bonded to a MET,

THE MET - yes. This is probably likely for the water but the gas may be external and separate.

close to the origin of the installation,

May not be close.

in addition to the bonding (to local Marshalling Point) in each of the dwellings?

It should be.

 

[JohnW2]

Yeeeessss. ....

Thanks for confirming my various points. Just one query ... on two occasions you wrote:

... the gas may be external and separate

What do you mean by that? Presumably the same principle applies as with water, with the pipe being bonded to the local EMT where it enters each dwelling (if it does - is that perhaps what you meant by 'may be external'??) and also to the MET (which may or may not be the same as one of the dwellings' EMT) where it enters the building? Is that correct?

Kind Regards, John

 

[EFLImpudence]

I have some flats where the gas does not actually enter the building until the external pipes reach each flat.

 

[JohnW2]

I have some flats where the gas does not actually enter the building until the external pipes reach each flat.

Oh, I see (I suppose the same might theoretically happen with water, particularly with a group of ground floor flats?). What happens then - do the gas pipes just get bonded to the EMT of each flat they enter, but not to 'the entire installations' MET', or what?

Kind Regards, John

 

[EFLImpudence]

That's all you can do because the meters are all outside.

 

[JohnW2]

That's all you can do because the meters are all outside.

True - and, in any event, if no gas pipe enters the communal parts of the building, then there presumably is no point/need to bond any gas pipes to the "entire installation's MET", anyway.

All this talk of Earth Marshalling Terminals is interesting, since it is something seemingly unknown to BS7671. Everything BS7671 says about main bonding (and this presumably is meant to apply to dwellings within multiple-dwelling buildings, as well as single dwellings) is in relation to a requirement to bond to the "MET".

Kind Regards, John

 

[EFLImpudence]

I suppose it is just a term used to distinguish between the two much the same as flats don't actually have a Ze - there is only one for the building..

 

[JohnW2]

I suppose it is just a term used to distinguish between the two much the same as flats don't actually have a Ze - there is only one for the building..

Fair enough. I suppose my point was that BS7671 does not use the term, and therefore is presumably calling the 'earthing point' within a flat an MET, even though you are suggesting that such is incorrect.

As for Ze, yes, I suppose what you say makes sense. However, as far as a flat is concerned, what really matters in the "Zdb" as seen within that flat, isn't it - effectively a flat's equivalent of a Ze? The fact that the flat's EMT/MET is slightly downstream of the building's MET is (assuming we're talking TN) really no different from the whole installation being a few metres further away from the substation, is it?

Kind Regards, John