Exporting Earth

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Shropshire
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Hi,

I have referenced the IEE Electrical "Electrical Installation Outdoors: A supply to a detached outbuilding" but am unsure about a few aspects of exporting earth.

In my example (recently upgraded earth bonding in the house), I will have 6mm SWA running from the house CU to the garage CU (3 core). The earth is being exported via the connection in the house CU all the way through to the garage CU.

I have no metal services (ie. taps etc) in my garage.

A T&E tail from the CU provides a supply to a junction box which is where the SWA is glanded from (source).. it then runs to a junction box in the garage where it is terminated. All along this route the 3rd earth core is connected via the tails of T&E to both CU's.

Now should I earth my SWA armour from the source via my newly added earthing block, and then earth it at the end of it's run to my garage CU. Is there any benefit in adding additional earthing in this manner ? if so, what size cable should I use for this ? Basically by doing this am I adding additional earthing which will provide a benefit.. ie. bonded to the house ?

I also understand I could always just earth it with the 3rd core of the T&E. Cost is no object, and I have no problem going above code/regulations so I have a proper install.

I am notifying and doing the work myself, so would additional thoughts like this give me brownie points when inspected by LABC ?
 
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From the conversion of twin and earth to SWA you will need to go to a metal adaptable box such as this://www.diynot.com/wiki/electrics:swa-gland.
The CPC (earth) of the circuit needs to connect to both the armour and the black core (sleeved gn/y).
You can do the same at both ends, or use a metal clad CU and terminate the SWA directly into that.
As you don't have any extraneous conductive parts there is no need to worry about main protective bonding (you may hear it referred to by its 16th edition name main equipotential bonding)
 

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