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Is A Tt Earth Required For A Site Supply ?


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#1 Alphonsox

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Posted 10 September 2015 - 12:36 PM

Over the last few weeks our electricity connection has been slowly progressing. We have had a new transformer fitted to a pole 100m away and a an underground cable and earth laid to provide a TN-C-S (PME) connection to the meter box.
Today we had NIE turn up to fit a meter in the box to provide a site supply. They refused to fit the meter due to the lack of a TT earth and stated that all site supplies must be TT earthed. This came as a bit of a surprise as I cannot see how a rod stuck in the ground can be anywhere near as safe as the TN-C-S system we have just had installed.

All I can think of is that is is due to the site meter they want to install
Can anyone confirm/explain this requirement ?

Edited by Alphonsox, 10 September 2015 - 12:37 PM.


#2 ProDave

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Posted 10 September 2015 - 12:42 PM

He is right, it should be a TT earth.

A PME earth may not be exactly at local earth potential, and in the event of a N fault can be a very long way from local earth potential. So for portable buildings (e.g static caravans) and site supplies they should be connected to a local TT earth and supplied via an RCD.

Your electrician should have known this and provided a rod, connected to an earth terminal in your meter box.

Up here, SSE normally expect at least one tested circuit before they will provide a supply, which is usually just the site power socket and it's earth rod.

EDIT

As Jeremy's reply below, my initial meter box is to remain as the final meter box location for the house.

It's no problem exporting the PME earth from the meter box to the house, while still providing a TT earth for the site socket and caravan.

Edited by ProDave, 10 September 2015 - 12:46 PM.


#3 jsharris

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Posted 10 September 2015 - 12:44 PM

The simple answer is "YES".

I argued that we were really putting in the final house supply, but with just a small CU to feed the site and the DNO (SSE) refused to accept a PME and insisted I TT it. It was no problem to bang a rod in to give them the TT connection, then take it out and PME the connection after they'd fitted the meter...................

#4 djh99

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Posted 10 September 2015 - 01:15 PM

Interesting. Our DNO is SSE as well. We built our garage and had our meter installed on that. No problems about earthing. Then we just ran the site from sockets inside the garage. I have no idea whether that somehow gets around the issue, or if the guys that installed ours simply missed the issue.

Correction: SSE isn't our DNO; they handle new connections for our supplier, Ebico. Our DNO is UK Power.

Edited by djh99, 10 September 2015 - 02:12 PM.


#5 Alphonsox

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Posted 10 September 2015 - 01:31 PM

Thanks for the replies. Our electrician was explicitly told by the cabling crew that a TT earth wasn't required as the meter was going into its final position (much the same argument as Jeremy's above). The meter install guy from the same company disagrees. Time to go and order a rod or two....

#6 ProDave

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Posted 10 September 2015 - 03:56 PM

You will end up with two earths in your meter box, the TT one for the site supply and the PME for the house.

I assume you have a CU in the meter box just for the site supply, so connect that to the rod, that's all you need to do.