Outbuilding Earth

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I'm after some opinions on some recent alterations to some outbuildings.
C50A MCB 35mm² 4C SWA to DB4
1657309457784.png
1657309573778.png
originally fitted about 2015 the exposed brass gland had insulating washers, but no sleeve, fitted, supposedly to isolate the TNCS from the local TT. 3 earth wires were TT spike and water pipe bond to internal earth bar. 3rd was added from source to earth bar 2020, effectively linking SWA armour, TT spike & TNCS.
As I understand it; Work done last week has insulated earth bar from enclosure, I don't know about the earth wire from TNCS source.

Cables on left are 16mm² split con. on right is 6mm². each ar fed with a C32 RCBO.

In particular:
1657310969260.png


1657311291323.png
Originally the splitcon earwas terminated in the grey block but the earthwire link to CU was not provided, the earth wire to the right is the TT spike. I don't know when the link was added. Blue socket was connected to B16 MCB on right.

Recently the SWA bottom left was added
1657315878644.png
for this plastic CU
1657315820193.png
The new SWA is 7C and I think 1.5mm², 3 cores each for L & N, 1 core for earth. The large earth wire is to earth spike.

I'm sure you all know my objections to brass SWA glands when not required, such as the feed to DB4 and new plastic CU but what opinions are there about the earth arrangements?
This sketch may help:
1657317411495.png

The reason i ask is I'm to provide power into tents and I'm wondering whether I should not extend what's there but provide my own earth spikes.
I've shown the earth from TNCS to DB4 in pink, it was as shown but I'm not sure where it connects to now.
There are other finals on the CU's and 4 more CU's fed from DB4 but all earth arrangements follow this design
 
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It does seem odd, a caravan has to be TT, but nothing about tents. We have the same problem were I work, EV-DB-Railway.jpg this says it is TT, but seems unlikely the box is TT, but the charging pod may well be TT, we also have sockets for powering out door equipment and common to see a caravan or motor home plugged in, I am not really worried as the building is steel frame, and is connected to the railway lines, so 8 mile of railway line should result in a good earth even if PEN is lost.

However there is a clear danger where TN-C-S is isolated to become TT, the metal should be far enough apart so you can't touch an item earthed to the PEN and TT at the same time, there are diagrams in BS 7671:2008 showing 1.25 meters clearance to side and below, and 2.5 meters above. Although with a caravan the fire regulations require 2.7 meters so if complying with fire regulations then should be no problem.

But father-in-law had caravan in his drive around a meter from the electric and gas cupboards which have the TN-C-S earth in them, and the caravan was on a hard standing so having done a risk assessment decided better to use the TN-C-S supply, as nothing really to touch near the caravan which was earthed to ground.

In the main one end of the SWA will go into a stuffing gland, so no earth exported, but the SWA will ensure an imbalance if cable damaged so will trip the RCD.

But where you show the socket can't see how you can get the distance? With the narrow boat only item plugged into mains supply was the battery charger, so the isolation transformer in the battery charger ensured no connection between the inverter 230 volt output and the shore supply.

So it is down to distance between TN and TT supply, and where an earth rod can be placed without it being near any earthed services, where I live there is no gas, so not so much of a problem, most electric cables are PVC covered, but still underground services are hard to trace, we have just installed extra drains, and found services we had no idea were there.
 
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I've been able to have another look at DB4.
The origin of this, DB4 was fitted in a wooden outbuilding in 2015, its fed with 35mm² 4C SWA from a 3P C50 MCB in DB1.
The brass gland was isolated from the enclosure with opaque washers, covered with the shroud and labelled as such.
1657750977484.png

It was designed from the outset as a TT board with an earth spike. There is water in the building and metal water pipes were bonded.

5 year inspection; 16mm² earthwire fitted from main earth bar in main building to earth bar, ie TT earth linked to PME.
1657751119966.png

At some stage the metal pipes were removed (stolen) so bond removed and second earth spike fitted.

This year another inspection; the insulating washers were removed and 16mm² PME moved from earth bar to enclosure
1657752592438.png
1657753427357.png

So it's gone from a fully TT board to one which I dislike with 2 unrelated earth systems, there was 7 Volts between them.
That twin earth system is exported to the metal DB in the adjacent toilet block where the 7 Volts exists between the DB about 2ft directly above the metal cased hand drier. It has 2 hand driers, 2 water heater on 16A MCB's and 6A lighting.
For completeness there are currently 5 DB's/CU's running on DB4 and another 2 huts/sheds to be connected to DB12
1657761096771.png

Are we all happy with all of the earthspikes connected together?
 

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