TT or TNC-s

[flyer]

Hi, Just doing some work in the garage for sign off, the garage is fed TNC-S from the house, with the addition of an earth to an adjacent spike, as in TT. There are no extaneous conductive parts in garage. trying to finish the paperwork on this and how to describe the arrangement.

Comments welcome

Flyer

 

[Engineer54]

In effect the rod has become an extraneous-conductive-part, that requires bonding back to the MET in the house.
This will require a minimum 10mm² copper bonding conductor.

There is absolutly no reason why you can't connect a good earth rod electrode to a PME installations MET!! In fact most European PME Regulations, Require a Rod electrode to be present at the installations MET... No reason why you shouldn't have a Rod or electrode at a TN-S MET either, in fact on most of the old council house estates of the 50's that's exactly what was provided...

 

[Des 56]

In effect the rod has become an extraneous-conductive-part, that requires bonding back to the MET in the house.
This will require a minimum 10mm² copper bonding conductor.

You are more often than not faultless when it comes to regulations and their interpretation so I need to tread very carefully

but the final part of its definition "not forming part of the electrical installation"would appear to me to exclude a rod ?
Your opinion would be appreciated

 

[flyer]

Just the point Spartykus.

The garage already wired this way, and have just changed a small radial cct to a ring. The earth from the TNC-s feed from the house is a1.5mm and increases to 4mm for the armour into gargae. The bonding onto the spike from the garage is 10mm to a spike. Not clear why this was required. House is 5 years old.
Have read most of over threads on the rights and wrong.

Flyer

Trying to make the paper work reflect the arrangement....

 

[Deleted member 26818]

There is absolutly no reason why you can't connect a good earth rod electrode to a PME installations MET!! In fact most European PME Regulations, Require a Rod electrode to be present at the installations MET... No reason why you shouldn't have a Rod or electrode at a TN-S MET either, in fact on most of the old council house estates of the 50's that's exactly what was provided...

Yes I agree, there is no reason why you can't connect a good earth rod electrode to a PME installation's MET.
However, in the UK the CSA of the conductor used, has to be a minimum of 10mm² if copper, or if another material is used, have the same conductivity.

 

[telectrix]

i would not be happy relying on a 1.5mm to carry a prospective TNC-S fault current

 

[Deleted member 26818]

You are more often than not faultless when it comes to regulations and their interpretation so I need to tread very carefully

but the final part of its definition "not forming part of the electrical installation"would appear to me to exclude a rod ?
Your opinion would be appreciated

That's why I used the term 'In effect' Des.

 

[SPARTYKUS]

:seeya:

What do you think then flyer? As Tel says the 1.5 bit is dire as the main earthing conductor.

Whats the rest of the set up, is the garage all protected by a 30mA RCD...? Or can you easily run a new bit of g/y back to the house...? Whats the score.

Doesn't sound like a good idea leaving it the way it is. Will you be paid for this extra work?

Returning to your orig post, it may be like that because a muppet did it :rifle:

 

[Engineer54]

Yes I agree, there is no reason why you can't connect a good earth rod electrode to a PME installation's MET.
However, in the UK the CSA of the conductor used, has to be a minimum of 10mm² if copper, or if another material is used, have the same conductivity.

Very true, i skipped over that bit didn't I !! ...lol!!

 

[flyer]

Thanks Spartykus

Yes there is a 30ma rcd in the gge CU. Very difficult to re wire from the armour join back to the CU in the house. I reckon they made a mistake in the original choice of wire from the house.

Flyer

 

[brman]

I'm confused. If the garage has an RCD and a earth spike with 10mm2 isn't in an acceptable TT system?
That is the way I read it from a 2005 IIE article on wiring sheds and garages. (from a thread here) Or has it changed since then?

The only thing I could find was "Where the installation inthe garage is supplied by an armoured cable, the armour or any protective conductor in the cable must not be
connected to and must not be simultaneously-accessible with any exposed-conductive-parts in the outbuilding"

 

[flyer]

So that takes me to my original question, Do i describe this as a TT system for installation certificate?

flyer

 

[telectrix]

only if you disconnect the SWA armour from the garage end will it be TT.

 

[Deleted member 26818]

If the installation, is connected to the TN-C-S installation, in the house.
Then it is TN-C-S, with an undersized earth/bonding conductor to the earth electrode.
The earth electrode has become one of the multiple earths, of the PME system.

 

[SPARTYKUS]

So will you be describing & legging it(!) or describing & disconnecting or.....

 

[flyer]

Is the best answer here to run a new earth to the CU in the house, and do without the earth and spike at the garage CU??

Flyer