Discuss Outbuilding with exported earth from main house, but also an earth spike... in the Electrical Forum area at ElectriciansForums.net

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DNS1

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As a scam inspection piece I'm looking at a rewire of my folks garage.

Going to be a really simple job, just adding a few sockets and updating the CU to a 17th edition board.

The supply to the building is a 15ish metre run of SWA from the main CU, sheath earthed to the MET.

Oddly though, it appears there is also an earth spike in place (not yet verified, but there is a length of green and yellow from the garage DB earth terminal which goes into the concrete outside.

The local substation is actually the same building as the garage (everyone else in this area has a double, we have a single with the substation in the other half) so I'd assume that I'd find the earth impedance on the spike to be pretty decent.

What would everyone else do in this situation?

Isolating the SWA sheath from the installation and treating as a TT?

Disconnect the earth spike and treat as a TN-C-S?

Leave both in place and work on worst case scenario?

To me, all of those sound fairly reasonable, but being a potential NIC inspection piece I'm being extra-cautious!
 
If there's a supplied earth that is TN, why not use it?

My initial thought, just wondered why someone went to the hassle of putting in an earth spike...

I guess I'll disconnect the spike, do Ze and if it's good then leave it disconnected...
 
I had the self same situation yesterday although it was around a 25m exported supply where the 2 core SWA which was jointed 3 times throughout its length was carrying the exported earth from the TN-C-S supply in the house and a spike was in situe at the garage end of the install. My decision was to run a new supply cable devorcing the TN earth at the house end and installing a new spike at the garage end to make it a stand alone TT situation in the garage.
 
Yo DNS

yeah sounds good. Wouldn't matter if you left it connected though apart from it looking confusing. It'll only help!

If there is a service in the garage it'll need a separate Main bond back to MET which is when all this becomes a pain. Potentially.
 
i've this unsettling feeling the earth rod hes found is for the dno transformer lol.
er , best reconnect it pretty damn quick. ;_D

HAHA!!!

I can imagine a comedy moment with the NIC inspector... Me holding a massive cable from a DNO earth rod and saying "Didn't need this so disconnected it!"

Amp David, the substation isn't actually in OUR garage! There's a brick wall down the middle to separate us from certain death thankfully!
 
As a scam inspection piece I'm looking at a rewire of my folks garage.

Going to be a really simple job, just adding a few sockets and updating the CU to a 17th edition board.

The supply to the building is a 15ish metre run of SWA from the main CU, sheath earthed to the MET.

Oddly though, it appears there is also an earth spike in place (not yet verified, but there is a length of green and yellow from the garage DB earth terminal which goes into the concrete outside.

The local substation is actually the same building as the garage (everyone else in this area has a double, we have a single with the substation in the other half) so I'd assume that I'd find the earth impedance on the spike to be pretty decent.

What would everyone else do in this situation?

Isolating the SWA sheath from the installation and treating as a TT?

Disconnect the earth spike and treat as a TN-C-S?

Leave both in place and work on worst case scenario?

To me, all of those sound fairly reasonable, but being a potential NIC inspection piece I'm being extra-cautious!

Check the TT connection if it has a good Ra value then leave it in place, connected to the garage EMT. All PME/TNC-S installations should have a locally driven earth rod. This is basically the rule in the rest of Western Europe, and makes perfect sense too, as it acts as another point of earthing the neutral on such systems.
 

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