TT earth rod to shed or non connected garage..advice please

[dogwind]

Hi i have been trying to find in either the osg or regs book where it states that a shed or garage not connected to the house must use a TT earthing system instead of using the house PME, i have been told from a Niceic that it must be TT and also been told by elecsa that a PME is ok to use, so i would like to know for sure what it correct. Thank you

 

[davesparks]

You won't find any regulation stating that you either can or can't.

You need to assess the requirements for bonding and establish whether it is better to extend the equipotential zone or set up a seperate earthing system if it is required.

GN8 has all the info along with very good diagrams.

 

[telectrix]

as usual niceic have got their stupid head on. what a load of bollox. see above post.

 

[dogwind]

Thanks for your replies, its been driving me mad trying to find it written down anywhere, i also had a nic electrician telling me the other day he was told he had to do an earth bond to a lightning condutor on a house which i feel isnt right, if it did get struck by lightning then that could then travel through all the earthing into the house, and unless i am wrong i think a lightning conductor is sort of like a TT rod and you are told never to combine TNCS PME earthing to a TT system with a connecting earth!

 

[davesparks]

Where are you getting this nonsense from?

Lightning conductors are an ECP and should be connected to the MET by a main bond.

Adding earth rods with a good Ra to the origin of a PME installation is a very good idea.

 

[Silly Sausage]

Dog, I hope you're not an NICEIC member and paying them your hard earned for incorrect advice.

Yet another NICEIC ------- for the collection!!!

 

[dogwind]

Regarding the lightning conductors its not something i have ever done myself but was told that you must never connect a TNCS and an earth rod (TT) earth together because if a fault develops on the supply side into the building it can use your PME system down along the earth rod for its fault path.

 

[Octopus]

Oh dear......

 

[davesparks]

Regarding the lightning conductors its not something i have ever done myself but was told that you must never connect a TNCS and an earth rod (TT) earth together because if a fault develops on the supply side into the building it can use your PME system down along the earth rod for its fault path.

Told by who?

For a start an earth rod does not automatically mean a TT system, both TNCS and TNS distribution employ earth rods too!

Have you read the regulations with regards bonding? They specify lightning protection systems as one of the items which require bonding.

A metal water or gas pipe can also present as low a resistance to earth as any lightning protection system, do you not bond them either?

 

[dogwind]

Yes forget the lightning rod bit it was just another thing on my mind, and yes i do bond the gas and water, When i did my electrical training (quite a few years ago now) i can remember someone asking about caravan points have to have its own earth rod and i asked why it couldnt have both earthing systems and he said about a fault from the TNCS system has the potential to go through the caravan and into the earth rod. Myself i think the more means of earthing a system getting the resistance down as low as possible has got to be a good thing.
Also a electrician i do alot of work with has just done the car charging point course that was an NICEIC one and he had said that all buildings not connected to the main house has GOT to have an earth rod for its earthing and must not use the pme earth, when the tutor was questioned about it by sparks on the course he said it seems a thing where older electricians use a rod while the newer trained ones do it wrong and use the TNCS house earth. Also regarding the water bond i have had people tell me if the water is in plastic pipe then you need to cut some copper into it so you can bond it, but it states in the OSG that if its plastic pipe then it dosent require bonding.

 

[telectrix]

caravans and car chargers are a different kettle of smelly swimmers. with PME systems, the loss of the supply neutral could cause problems as a caravan has a metal skin. so TT is used . i imagine it's a similar scenario for the car charging points.

 

[dogwind]

caravans and car chargers are a different kettle of smelly swimmers. with PME systems, the loss of the supply neutral could cause problems as a caravan has a metal skin. so TT is used . i imagine it's a similar scenario for the car charging points.

It was the car charging points that has got me thinking about outbuildings must have a an earth rod because of what my mate who has been on the course said... going by the NIC insturctor both him and myself have been doing it wrong for years but ELECSA have told us we doing it right...god knows who is right.

 

[davesparks]

Forget what the NICEIC and ELECSA have to say and read the sodding regulations!

It is all explained clearly in guidance note 8, with nice clear pictures too!

 

[dogwind]

I will get it back out and have a read through it again, just makes you doubt yourself when so called experts are telling you different things all the time.

 

[trev]

The NIC are reknowned for making up their own regulations mate. None of them have any basis in fact.
An example is the nonsense they came out with a couple of weeks ago that anything which tests out at greater than 6.6 K ohms did not need to be bonded.

 

[Simonslimline]

Yes forget the lightning rod bit it was just another thing on my mind, and yes i do bond the gas and water, When i did my electrical training (quite a few years ago now) i can remember someone asking about caravan points have to have its own earth rod and i asked why it couldnt have both earthing systems and he said about a fault from the TNCS system has the potential to go through the caravan and into the earth rod. Myself i think the more means of earthing a system getting the resistance down as low as possible has got to be a good thing.
Also a electrician i do alot of work with has just done the car charging point course that was an NICEIC one and he had said that all buildings not connected to the main house has GOT to have an earth rod for its earthing and must not use the pme earth, when the tutor was questioned about it by sparks on the course he said it seems a thing where older electricians use a rod while the newer trained ones do it wrong and use the TNCS house earth. Also regarding the water bond i have had people tell me if the water is in plastic pipe then you need to cut some copper into it so you can bond it, but it states in the OSG that if its plastic pipe then it dosent require bonding.

A test to verify if it is extraneous or not should be carried out to confirm if bonding is or is not required. Again GN8 explains this.

 

[telectrix]

as above. if incoming water is plastic, then no bonding required. any metal pipes should be tested to see id they are extraneous or not. IR test from suspect pipe to MET. if reading is >22kΩ, then it's NOT extraneous, and does not require bonding. forget any niceic made up figures.

 

[dogwind]

The NIC are reknowned for making up their own regulations mate. None of them have any basis in fact.
An example is the nonsense they came out with a couple of weeks ago that anything which tests out at greater than 6.6 K ohms did not need to be bonded.

I have never registered myself with NIC but i used to work for a company that was and after i saw the work and stuff that was going on i decided i never would do.
A customer i work for had some electrical work done that was very bad and she contacted the council building control and was told by them they havent got time to follow it up, and would only come out if she had been hurt or maybe a fire. just shows the whole part P thing is a farce.

 

[Engineer54]

Hmmmm, now i wonder how the DNO's manage to provide all those Protective Multiple Earths in PME and even the TNC-S installations?? And NO, TNC-S isn't the same as PME!!

TT earth (rods mats, tapes etc) can be mixed with ANY of the TN earth systems, (TN-S, TNC-S, PME). It is not recommended that TN systems are mixed!!

Ignore anything a NICEIC spokesman states without confirmation from a known trusted source (that you'd be better off seeking in the first place anyway) .... Oh and it is now acceptable to use a domestic PME supply for car charging points!!

 

[Engineer54]

as above. if incoming water is plastic, then no bonding required. any metal pipes should be tested to see id they are extraneous or not. IR test from suspect pipe to MET. if reading is >22kΩ, then it's NOT extraneous, and does not require bonding. forget any niceic made up figures.

Just because a service water or gas pipe enters a building in plastic doesn't mean that the rest of the internal metal pipework will not be extraneous. Depending on the construction method of the building (especially concrete framed c/w concrete floors and ceilings) as well as the installation of the pipework, these metal pipes can very easily pick up extraneous potentials from the buildings fabric. That's why you should always test and not assume anything, even when the incoming supply pipes are in plastic....