TT system what set up would you use

[Welchyboy1]

have to re wire an industrial unit and surrounding work shops but in two minds of how to install

currently there is NO EARTH for the whole site, the place consists of a large storage shed with the mains coming in, TPN 100a supply, the place at the moment is a death trap

no current RCD protection at all(not that it would help with there being no earth)

Loop test between L1/2/3 and N is 0.57ohms and has been confirmed no PME connection is available

4 surrounding buildings rented out, few workshops, 1 mechanics hut, mainly lighting and sockets with 2x tpn hydraulic ramps, no major loads

proposed new install will be

TPN dist boards in each building, 16mm swa submains from each outbuilding back to 63a switchfuses via 100A busbar to origin



my plan was to have a 300mA s type 4 pole RCD at scource with earth rod 2x large coupled together



either 30mA rcd main switches at all distribution boards, or mainswitch isolators and 30mA DP rcbos for additional protection as required

thing is im a bit nervous about this install as i know whatever set up i choose nusiance tripping is likely in the future and may take out the whole site in some cases, so im leaning towards the 30ma RCD mainswitch at each dis board so i can at least keep a fault from knocking out all the sites at once and keep it local to the building affected

most of the existing final circuits are staying for now(i am pushing for a full site re-wire but have to start at the distribution for now)and there are lots of bodges and add ons all over the place

i have made agreements with the landlord to correct C1 and C2 faults with the testing as i find them at extra cost

have a feeling this one will bite me on the bum in the future

any input? have i missed any thing that could improve the RCD set up or other suggestions?

 

[Engineer54]

Not really considering we're only talking about a 30m run from the main intake to each rod. For a site this size I'd say it was fine. That's my opinion anyway, it's what I was taught as a lad, it's what I have always done and it's what I will continue to do.

Any links to further info about the subject of muliple earth rod installations and the most effective distance between them would be much appreciated though. I'm not too stubborn to learn why what I'm doing is OTT if indeed it is!

I'll see what i can dig up and get back this evening!!


Off out on site now, ...some of us have got to work while you lot are far away in the land of Nod!! lol!!

 

[GLENNSPARK]

I'll see what i can dig up and get back this evening!!


Off out on site now, ...some of us have got to work while you lot are far away in the land of Nod!! lol!!

not going out shopping then?..lol

 

[Richard Burns]

This basic document on P7 says multiple rods should be installed at a spacing greater than their depth.
View attachment Earth Electrodes And Earth Electrode Testing (1) (2).pdf

This slightly more HV one, in section E5 seems to use a standard spacing of 3.6m for 2.4m rods.
View attachment East Earthing Manual Feb 2002.pdf

This one on pages 40/41 states that rods should be separated by at least their insertion depth
View attachment pub-119-earthing-practice.pdf

However this does not mean I fully understand everything they are saying!!
Just some references.

 

[Engineer54]

Grateful for R Burns to post those PDF's above, as i don't have a PDF of the data i typically use. But generally concludes with that of the ''East Earthing Manual'' above, except it goes into a little more detail of when you need to extend distances between connected rod/electrode positions. That will generally be down to soil conditions, eg the better (lower resistivity values) the soil conditions, the greater the distance required, so as not to overlap zones of influence, but i hasten to add, will also generally require less rod positions, if working to attain a specific Ra value.

I'm far more used to installing ground fields (ground nests) and based on soil resistivity and the depth of rods, we will generally space the rods to 1.5X to 2X the depth of rod, and occasionally up to 3X. On a grid system of say 30 rods (wow!! ....just thought about the amount of land needed if working to 10 times the driven depth...lol!!) each will be tested for both active individual Ra value, and for any deterioration in that plateau value caused by adjacent rods, which if present, will clearly show a dip in that plateau. Rarely have i ever seen that plateau dip during final testing. BTW all our rods are copper clad steel 3.2m X 3/4'' supplied by the industry leader in all things on Earthing!! ...lol

 

[D Skelton]

Cheers RB, I shall have a read through them later