SWA Sub Main advice/comments

[TheCodboy]

OK, so you just need to meet the SWA fault protection so RCD up-front on basically any SWA choice, and a rod arrangement below 200 ohms. What is the surrounding soil/ground like?

Haven't had a dig yet but I've been looking at bentonite if I'm struggling for a good reading.

 

[timbobelfast]

Hi all, looking for a bit of advice and confirmation on my proposed plans for a SWA sub main to a ISO metal storage container. I've calculated the max demand in the ISO will be about 20A (300w of led lighting and 2 double sockets for chargers etc) It will be fed from a 3ph DB in another building. The cable run is 100 meters, I'm planning on using 16mm 2 core swa ( Volt drop calcs allow about 35A with 16mm) and installing a rod at the container (the vast majority of the cable run is at height, clipped to the building). The container will have a small 4 way board with RCD main switch.
The 16mm will be fed from a C32 breaker in the 3Ph board. Im installing double insulated 16mm tails and a 16mm earth from the 3ph DB to a meter (needs a meter installed) then from the meter to an adaptable box where I will terminate the SWA. Due to the fact that I'm using a rod at the other end, I'm planning on a 100ma S rcd for fault protection for the SWA (inside the adaptable box).
Can anybody see any glaring errors in my method? I have spoke to Napit and they were fine about my proposed plan, but they didn't mention the 100mA rcd.
Thanks in advance!

I take it the Earthing System for the upstream supply is a TN-C-S???

 

[pc1966]

Haven't had a dig yet but I've been looking at bentonite if I'm struggling for a good reading.

Clay cat litter is cheaper and the same sort of stuff!

Obviously check for any buried services as far as you can. There are sites like this for main stream power & gas, but not everyone is on there:

LSBUD - Home

LSBUD is the free to use Safe Digging Platform providing Utility Asset Maps for over 3,9 million searches every year across the UK.

lsbud.co.uk

Also remember that the main factor is soil conductivity is moisture, so if you can go deeper (say 8' = 2.4m rod, typically in two sections) you will generally do better than two short ones in parallel as more chance of the soil remaining moist.

I have used M16 stainless studding as an earth rod driven in like a giant drill (SDS adaptor and a 1/2" drive stud runner), but obviously you get purpose made ones and matching bit like access boxes, etc. For example:

Earth Rods & Fittings Archives - Kingsmill Industries

kingsmillindustries.com

Earthing Archives

Browse our range of Earthing & Lightning protection equipment and products online at AN Wallis including earth Rods, Bars, U Bolt Clamps and more.

www.an-wallis.co.uk

 

[TheCodboy]

Clay cat litter is cheaper and the same sort of stuff!

Obviously check for any buried services as far as you can. There are sites like this for main stream power & gas, but not everyone is on there:

LSBUD - Home

LSBUD is the free to use Safe Digging Platform providing Utility Asset Maps for over 3,9 million searches every year across the UK.

lsbud.co.uk

Also remember that the main factor is soil conductivity is moisture, so if you can go deeper (say 8' = 2.4m rod, typically in two sections) you will generally do better than two short ones in parallel as more chance of the soil remaining moist.

I have used M16 stainless studding as an earth rod driven in like a giant drill (SDS adaptor and a 1/2" drive stud runner), but obviously you get purpose made ones and matching bit like access boxes, etc. For example:

Earth Rods & Fittings Archives - Kingsmill Industries

kingsmillindustries.com

Earthing Archives

Browse our range of Earthing & Lightning protection equipment and products online at AN Wallis including earth Rods, Bars, U Bolt Clamps and more.

www.an-wallis.co.uk

Just did a job today where a house had no main earth. Did a Zs at the sockets and it was 290 Ohms. Did as bit of digging out, probably a couple of feet and got the 4ft rod pretty much all the way in. Ze of 28 ohms. That'll do for me!