Consumer unit upgrade TT system

[monkeyhanger]

Appreciate a bit of advice regarding this that I'm doing in the morning-

Consumer unit upgrade in house with 6mm gas & water bonding existing (leaving bonding as it is). Existing rod in house with 6mm up to CU.

(Existing install) From a TT system in the house there is a 2.5/1.0 T&E running to a detached outhouse (perhaps, four meters from the back of the house) feeding an existing fuseboard in there with BS3036 fuses for 15A sockets radial and 5A one light.

The outhouse has a copper water pipe supplying a washing machine. This isn't bonded where it rises from the concrete floor in the outbuilding and there isn't a seperate rod in there. The only earthing of anything in there is the 1.0mm CPC of the T&E submain & CPCs of light/sockets.

Am I right in thinking that the CPC in the T&E won't suffice in the requirements for equipotential bonding in the outbuilding (it appears that the T&E is ran under the concrete back yard in plastic conduit.. many years ago). If I install a rod & earth conductor to the existing BS3036 unit in the outbuilding and bonding between this unit & the copper pipework in the outbuilding, should I insulate the 1.0mm CPC in the T&E submain from the outbuilding installation (at the outbuilding end)? Or leave it connected at both ends- in the house and the outbuilding. If either is acceptable would it be best practice to leave it connected both ends?

I am quite aware of requirements when exporting TNS and TNCS but I've never came across TT in the main building with an outbuilding where bonding is required.

This is hopefully obvious to one of you who may read this before tomorrow

 

[monkeyhanger]

Because I want to know what the "bare minimum" is that will comply for me to be able to upgrade the consumer unit in the house and reconnect the submain. I don't want to tell them that the tenant needs to take a day off work & move all their furniture & all the flooring needs to come up etc. to put a new submain in from the front door to the outbuilding over the back yard IF IT ISN'T NECESSARY!

"What is the point in asking questions" whats the point in the tone of these replies-
"Something is certainly obvious, but i'll limit my comments to the job you are asking about"
"What do you mean by 'especially for a letting agent'? Are their lives worth less than other peoples and so it's ok to install substandard earthing ?"
"To be honest i just can't be arsed"
"He'll probably just bung a twig in and call it a day"
I think you're trying to help but equally you want to shoot me down at the same time haha

Please tell me what would be wrong with the following-
Keep existing 2.5mm submain from 20A 30mA RCBO in house.
Disconnect 1.0mm CPC of 2.5 t&e in outhouse.
Install rod & bonding in outhouse.

Be as condescending as you like if you answer the question

 

[Deleted member 9648]

Your OP reads as though you haven't got a clue how to install a TT system properly. It sounds like you are planning to have just a single rod for the main earth and that you don't understand either the regulations concerning earthing of multiple buildings nor the theory behind them.

Go on then,what are the regulations then? Where is there a requirement for more than one earth electrode for a multiple building install from the same source of supply?

 

[davesparks]

Go on then,what are the regulations then? Where is there a requirement for more than one earth electrode for a multiple building install from the same source of supply?

The regulations require that any Protective conductor common to multiple buildings or earthing systems be sized adequately to handle the highest possible fault current from either installation. GN8 is the best source of info on this with clear diagrams and explanations.

There is no regulatory requirement for multiple electrodes in that situation, bit I never said there was.
I have said multiple rods will be required to make up an acceptable electrode, but this was based on the assumption that standard 4' rods will be used, obviously if he uses 10' rods then it's a different story

 

[Deleted member 9648]

The regulations require that any Protective conductor common to multiple buildings or earthing systems be sized adequately to handle the highest possible fault current from either installation. GN8 is the best source of info on this with clear diagrams and explanations.

There is no regulatory requirement for multiple electrodes in that situation, bit I never said there was.
I have said multiple rods will be required to make up an acceptable electrode, but this was based on the assumption that standard 4' rods will be used, obviously if he uses 10' rods then it's a different story

"It sounds like you are planning to have just a single rod for the main earth and that you don't understand either the regulations concerning earthing of multiple buildings nor the theory behind them."

Well I'd suggest the above statement is somewhat misleading concerning regulations.
Personal preference on earthing is another matter, but on so many threads on TT installs personal preference seems to be confused with actual requirements.

 

[davesparks]

"It sounds like you are planning to have just a single rod for the main earth and that you don't understand either the regulations concerning earthing of multiple buildings nor the theory behind them."

Well I'd suggest the above statement is somewhat misleading concerning regulations.
Personal preference on earthing is another matter, but on so many threads on TT installs personal preference seems to be confused with actual requirements.

The above statement was a reply to his request that I share the opinion that I previously had said I would keep to myself.

I cannot see how the statement could be misleading to anyone with a working knowledge of the English language.

 

[GMES]

Guys please keep the thread on track and leave the bickering out of it.

 

[Knobhead]

Personal preference on earthing is another matter, but on so many threads on TT installs personal preference seems to be confused with actual requirements.

What are the actual requirements?

 

[Deleted member 9648]

What are the actual requirements?

You'll find them in Bs 7671.
If it's not in there it's not a requirement.
A prime example is the NICEIC 'max Ra of 100 ohms'.

 

[davesparks]

What are the actual requirements?

You'll find them in Bs 7671.
If it's not in there it's not a requirement.
A prime example is the NICEIC 'max Ra of 100 ohms'.

BS 7671 is not teh be all and end all, there is a seperate british standard (BS7430 'Code of practice for protective earthing of electrical installations') specifically for earthing which is referenced in bs7671.

BS7671 requirements are pretty straight forward, it needs to be designed to withstand damage, allow for increase of resistance due to corrosion, be of a type and depth that soil drying and freezing will not increase the resistance above that required.
A 4' rod is not going to be deep enough to avoid drying out or freezing from affecting it.

 

[trev]

What are the actual requirements?

A joke

 

[Deleted member 9648]

A single rod is not necessarily only 4ft long.
The only point I want to make here is that regardless of whether you approve or not the lacklustre requirements of bs 7671 with regards to TT systems are nevertheless the only requirements an electrician carrying out a small TT system need comply with.
By all means slate those requirements as wholly inadequate but please dont forward your own views on it as 'requirements'.

 

[davesparks]

Please tell me what would be wrong with the following-
Keep existing 2.5mm submain from 20A 30mA RCBO in house.
Disconnect 1.0mm CPC of 2.5 t&e in outhouse.
Install rod & bonding in outhouse.

Be as condescending as you like if you answer the question

If that water pipe you bond in the outhouse is actually extraneous then it will more than likely provide a much lower resistance earth path than the rod you install, potentially making that rod redundant and pointless. Now if you took the time to read your regulations book you would know whether it is acceptable to use the water pipe as an earth electrode or not, and if it is acceptable to use the water pipe as a bonding conductor.

Regulations 542.2.6 and 543.2.1 are concerned with this, GN8 gives further help on understanding them. If the water pipe is privately owned, you can take precautions against it being disconnected and it has suitable CSA then the absolute bare minimum allowed by the regulations may not require you to add any rods.

 

[stevethesparks]

Just to throw a spanner in the works;
A possible scenario could be that a Water/Gas supply combination could be of a much lower resistance than can be achieved by earth rod in some area's. With BS7671 not permitting the use of such a means as an earth path (unless privately owned) then where does an electrician stand having to connect all to the MET, as effectively such an installation will be heavily reliant on the extraneous pipes?
Considering some premises may not have the opportunity for additional rodding or plates etc.

 

[Leesparkykent]

Just to throw a spanner in the works;
A possible scenario could be that a Water/Gas supply combination could be of a much lower resistance than can be achieved by earth rod in some area's. With BS7671 not permitting the use of such a means as an earth path (unless privately owned) then where does an electrician stand having to connect all to the MET, as effectively such an installation will be heavily reliant on the extraneous pipes?
Considering some premises may not have the opportunity for additional rodding or plates etc.

look at the post above yours.

 

[Silly Sausage]

A 4' rod is not going to be deep enough to avoid drying out or freezing from affecting it.

Frigging hell Dave, we're not in the Arctic Tundra!