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Bonding in a Garage


Sam7

Question

Hello all

I have a quick question.

I am upgrading a c/u and it's circuits in a detached garage.

The current c/u is connected to the house Consumer unit (on the RCD side) via 4mm 3 Core SWA.

As the garage is a TT system, do i need to install an earthing rod instead of the SWA's Earth or is the current 3 core SWA sufficient ?

The new circuit will consist of a 2way lighting circuit and a radial with 3 2G sockets.

Thanks

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10 answers to this question

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Sam - I don't understand!

Are you saying the garage already has a rod??

Is the SWA earthed from the CU and then isolated at the garage? So the garage's earth is TTed?

I don't see how the garage can already be TT and you are asking if you need to insert a rod?

What's the house's earthing arrangement?

And welcome

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Sorry Apache.

The garage does not currently have a Rod but i ask this because surely a detached building should be classed as a TT system, or am i wrong ?

The SWA is earthed from the house c/u (3core SWA) to the Garage, from where the old system is then run.

The house is TNS

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Sorry Apache.

The garage does not currently have a Rod but i ask this because surely a detached building should be classed as a TT system, or am i wrong ?

The SWA is earthed from the house c/u (3core SWA) to the Garage, from where the old system is then run.

The house is TNS

I'm no spark but I expect the advise will be to TT the outbuilding!

:D

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Evans Electric

On a TNS system you can use the earth from the main board . Any other method and the lid of the dreaded can of worms begins to unscrew. So the garage isn't actually a TT. I'd say the set up was fine myself.

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I have got a job doing almost the same as you and I will be putting a rod in. The only difference with mine is, at the moment the garage is fed by a 4mm T&E suspended from the house. The guy is eventually going to have a cable buried, but at the moment I'm a little worried with how it is now.

Malc

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There's nothing wrong with exporting the earth from the house on a TN-S system as long as the disconnection times are met ... there's likely to be an RCD in a new garage cu so this would help if the times are a little close to the maximum allowed ..

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Indeed - There is nothing wrong with exporting the earth on a TN-S system.

I know that NICEIC assessors (Down here, at least) like to see the SWA armour - Earthed from the Source (TN-C-S). BUT the earthed armour ends where it enters its destination. And Not taken into the CU. (Has to be terminated before it enters any Metal Clad CU).

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Ok I went on our NICEIC inspection last week and put this question to him.

He told us there was no distance PME couldn't be taken outside the building as long as disconnection times could be met, and in fact said we could even install a rod making it TT, at say the shed linking the 2 systems together. After questioning about this he insisted that this was OK as all transformer's are staked down to Earth.

Still not convinced but thats what he told us CJS

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The argument will go on for ever. I personally TT all outbuildings that are seperate from the house. As said dno do not allow pme to seperate buildings on tncs well edf don't anyway. You have got to do what you are happy with. As for NICEIC its not really anything to do with them what I do.

Batty

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Indeed - There is nothing wrong with exporting the earth on a TN-S system.

I know that NICEIC assessors (Down here, at least) like to see the SWA armour - Earthed from the Source (TN-C-S). BUT the earthed armour ends where it enters its destination. And Not taken into the CU. (Has to be terminated before it enters any Metal Clad CU).

So best to attach an earth rod and not the swa then.

I was going to contact Elecsa to make sure but wanted you guys thoughts on it. The garage c/u is metal clad by the way.

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