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All the outbuildings I do have a seperate earth TT so will be very different to ZE at house unless that is TT also.
Testing Ze for a new consumer unit in a garage
- Thread starter matt1987
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Help Support Talk Electrician Forum:
batty,
Ze at an outbuilding on the end of a sub main, can never be Ze mate!
Ze is defined as the earth fault loop impedance external to the installation.
This must be measured at the origin of the installation, i.e. at the DNO "head".
It can never be measured anywhere else in the install and be a real true Ze.
It may be an effective Ze but it can not be recorded as such in accordance with the definition in BS7671.
:Salute
Ze at an outbuilding on the end of a sub main, can never be Ze mate!
Ze is defined as the earth fault loop impedance external to the installation.
This must be measured at the origin of the installation, i.e. at the DNO "head".
It can never be measured anywhere else in the install and be a real true Ze.
It may be an effective Ze but it can not be recorded as such in accordance with the definition in BS7671.
:Salute
I'm afraid I'm with Batty on this one.
If the outbuilding has a seperate TT earth, then you would treat this as a 'seperate' installation - i.e. -
You would measure Ze (or Ra, depending on method) at the outbuilding CU, with the rod 'earthing conductor' disconnected.
Any 'Extraneous Conductive Parts' within the outbuilding would be bonded to the MET in the outbuilding - not the MET in the house............all needs to be kept seperate.
Test results for outbuilding CU and 'earthing arrangements' would be recorded on additional sheets.
BUT, the Zs for the 'Distribution Cable', from main building to outbuilding, would still be taken at the 'outbuilding' CU and recorded on the Main Building Installation certificates.
ADS,
You cannot do this and comply with the definitions in BS7671.
There is no interpretation possible here with regard to this sorry.
We are talking here about definitions of values from the standard.
These are black and white.
You cannot deviate from the definitions, else you are talking about a different value.
Check the definition of an installation or a system.
Have you possibly not even considered mixed earthing systems in the outbuilding,g have you, any of you, perhaps?
You can only have one MET in an install.
Any other "main" earthing terminal is a BEMT, a Building Earth Marshalling Terminal.
Now unless this stays civil and polite, I will not post any more in this thread, and I will have no hesitation in reporting any abusive posts to the mods and the admins.
IF, we can all stay polite and civil, we can discuss this further.
HOWEVER, if you choose to do this, please back up your definitions with the appropriate regulations, definitions, or irrevocably sound science!
You cannot do this and comply with the definitions in BS7671.
There is no interpretation possible here with regard to this sorry.
We are talking here about definitions of values from the standard.
These are black and white.
You cannot deviate from the definitions, else you are talking about a different value.
Check the definition of an installation or a system.
Have you possibly not even considered mixed earthing systems in the outbuilding,g have you, any of you, perhaps?
You can only have one MET in an install.
Any other "main" earthing terminal is a BEMT, a Building Earth Marshalling Terminal.
Now unless this stays civil and polite, I will not post any more in this thread, and I will have no hesitation in reporting any abusive posts to the mods and the admins.
IF, we can all stay polite and civil, we can discuss this further.
HOWEVER, if you choose to do this, please back up your definitions with the appropriate regulations, definitions, or irrevocably sound science!
Im on the side of only ONE Ze,ADS,You cannot do this and comply with the definitions in BS7671.
There is no interpretation possible here with regard to this sorry.
We are talking here about definitions of values from the standard.
These are black and white.
You cannot deviate from the definitions, else you are talking about a different value.
Check the definition of an installation or a system.
Have you possibly not even considered mixed earthing systems in the outbuilding,g have you, any of you, perhaps?
You can only have one MET in an install.
Any other "main" earthing terminal is a BEMT, a Building Earth Marshalling Terminal.
Now unless this stays civil and polite, I will not post any more in this thread, and I will have no hesitation in reporting any abusive posts to the mods and the admins.
IF, we can all stay polite and civil, we can discuss this further.
HOWEVER, if you choose to do this, please back up your definitions with the appropriate regulations, definitions, or irrevocably sound science!
after all, you only have ONE earthing conductor,
even if you have a TNCS with localised rodding its still only one MET at the source, doesnt matter where you earth your rods too, they are merely BEMT's.
No mixed earthing systems sidewinder - that's why you have to do what I describe.
If you choose to 'rod' the outbuilding that is supplied by a distribution circuit off a TN system, then you have to keep the earthing systems seperate.
To do that, you would terminate the TN earth at a suitable point where it enters the outbuilding and keep it seperste from the TT earth that you are introducing to the outbuilding.
The outbuilding then becomes a seperate install with it's own earthing system - TT
How else could you possibly do it??
---------- Post Auto-Merged at 20:17 ---------- Previous post was made at 20:15 ----------
If you choose to 'rod' the outbuilding that is supplied by a distribution circuit off a TN system, then you have to keep the earthing systems seperate.
To do that, you would terminate the TN earth at a suitable point where it enters the outbuilding and keep it seperste from the TT earth that you are introducing to the outbuilding.
The outbuilding then becomes a seperate install with it's own earthing system - TT
How else could you possibly do it??
---------- Post Auto-Merged at 20:17 ---------- Previous post was made at 20:15 ----------
But Steps, if you stay true to form and don't 'export' the PME supplied earth to the outbuilding, how can you possibly have only one Ze - what about your 'rod'??
ADS,
OK no mixed earthing.
However, IF you have a water pipe from the house which is PME then you HAVE mixed earthing, end of, unless it is isolated by a section of polymer pipework.
Yes you do need to separate the earthing systems if you rod an outbuilding and that includes all of the possible earthy services and any structural steelwork, which would be impossible in many situations.
Yes that could be one way of separating the earthing systems if that were possible.
The outbuilding does not become a separate system, check the definitions.
OK no mixed earthing.
However, IF you have a water pipe from the house which is PME then you HAVE mixed earthing, end of, unless it is isolated by a section of polymer pipework.
Yes you do need to separate the earthing systems if you rod an outbuilding and that includes all of the possible earthy services and any structural steelwork, which would be impossible in many situations.
Yes that could be one way of separating the earthing systems if that were possible.
The outbuilding does not become a separate system, check the definitions.
has an Ra, NOT a Ze,
I can honestly see where you are coming from,
but, IMHO, if you are taking the earth from the house to the shed then you simply have a Zs at the shed end, whether or not you wish to even use it is up to you,
MY BLUE
If you seperately 'rod' an outbuilding, how can you possibly treat the whole thing as one installation.
So, you record your Ze as 0.28 - because that's the measurement at the incommer and then what....
.....you measure the Zs of your socket outlet circuit in the outbuilding as 115 ohms (because of the rod) and record this on the same sheet??
What do you put on the form when it asks for Earthing Arrangements - do you tick two boxes?
Means of Earthing - tick both boxes again??
What's your PFC - 821 Amps.......not at the outbuilding it's not.
How can you possibly treat it as one system/installation?
Come on, where are all the 'I always Rod a shed' brigade............How do you do your forms????
---------- Post Auto-Merged at 20:52 ---------- Previous post was made at 20:50 ----------
What about Zs of the shed circuits??
Ze would be at service head. your outbuilding would have a Ra. means of earthing for shed DB would be the rod. simple. (at least thats how i usually do it)
my certs have a little box at the top for a DB/CU NOT connected directly at the source of the installation, with readings for Zs etc at that point.
maybe if you are doing remote installs everyone who does them should have this sort of arrangement.
What about it mate?
Zs(DB) is the figure that goes at the top of the schedule page for the sub-board; but on page 2; "particulars of installation at the origin", can only be the HED; unless you want to have 2 origins??
The final circuits at the sub-board have their individual Zs readings on the schedule, as normal - surely anyone (knowledgeable) reading the cert. will understand the readings? Besides, you would have stated on the cert. what works had been done......
Yes?
KME
you can have more than 1 installation. so you could treat the shed as its own installation, with its own MET etc if you wanted
Here's what I would do if I was supplying power to an outbuilding with it's own means of earthing.
EIC & Schedules for the outbuilding - ticking 'New' installation - and continue as normal.
EIC & Schedules for existing installation - ticking 'Addition' for sub-main distribution circuit.
Obviously, if I'm running the 'existing' installation earth to the outbuilding, then it's one set of certs.
Am I wrong??
EIC & Schedules for the outbuilding - ticking 'New' installation - and continue as normal.
EIC & Schedules for existing installation - ticking 'Addition' for sub-main distribution circuit.
Obviously, if I'm running the 'existing' installation earth to the outbuilding, then it's one set of certs.
Am I wrong??
nothing, lots of installations have more than one source of supply,
UPS, generators etc,
but are they all fed through the same origin or seperate circuits?
the law states you cannot have a supply capable of backfeeding, so if you have more than one "actual" source of independant supply then it MUST be independant of the whole installation.
does that make sense? probably not, :|
Manator
©Honorary Essex Boy™
I think you are getting confused as to what is and what is not an installation, and when it is divided, it is still an installation, regardless of how many DB's are used. Or indeed if any other earthing arrangements are utilised.
Manator
©Honorary Essex Boy™
If the regulations are confusing you, I suggest you read them again, I would also suggest that understanding the regulations, is not the same as quoting them. I can only quote the regulations you have previously mentioned, however I think I must look at them very differently.
I think you may need to check what is a "system" under 7671 and explain the situation with respect to this.
Please remember this is all with regard to staying within the remit of 7671, as if we go outside this then other requirements are needed.
Please remember this is all with regard to staying within the remit of 7671, as if we go outside this then other requirements are needed.
Reg. "GROUP" 542 as I doubt, it is a SINGLE REG. is WHAT exactly, that you feel it justifies you WHOLE argument.
I don't have 7671 to hand & I am not digging it out now, so, please, as I said earlier quote this to justify your argument else we cannot see how this is relevant.
I don't have 7671 to hand & I am not digging it out now, so, please, as I said earlier quote this to justify your argument else we cannot see how this is relevant.
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