Garden room

[Pat Tester]

Hi chaps, any chance of some input. I have been asked to wire summer house from cottage. TT system Ze 32.4 ohms, R1+R2 of supply cable 0.09 ohms Question If I put a new rod in for the summer house should I 1) use the cottage MET and the new rod
2) only use the cottage P+N and use new rod for summer house cpc and armour
3) don't fit a new rod and just use the cottage MET 4) tell them it doesn'e need an earth
as the cottage is made from wood (joke) Thanks in advance

 

[Shakey]

use rod for summer house, wire in SWA, but connect armour as CPC at house end only, armour should be insulated at summer house end

presuming CU is already on an RCD, this will pick up any faults to earth at the summer house, even without exporting the CPC

 

[Pat Tester]

Thanks for reply, the cottage has old earth trip only, 2 consumer units in kitchen cupboard
with seperate metal clad switch to kitchen sockets, wired out back on one consumer unit. 2 6mm T&E feeds to 2 wooden boxed fuse baords with ceramic fuse holders. cables clipped to beams. 2.5 swa run to garage, no earth on armour. loose cables in loft. Cottage is thatched ! I am going to do full survey / test for re wire. Would you put another eatrh rod in for cottage to lower Ze ?

use rod for summer house, wire in SWA, but connect armour as CPC at house end only, armour should be insulated at summer house end

presuming CU is already on an RCD, this will pick up any faults to earth at the summer house, even without exporting the CPC

Just re read your reply, Are you suggesting that the eath at garden room is only conected
at new earth rod and not back to cottage ?

 

[slrichardson]

Ze seems ok to me think it has to be less than 200 ohms for tt, so wouldn't need extra rod at cottage.
I would also rod at garden room as suggested by shakey and use small cu with rcd

 

[Shakey]

Thanks for reply, the cottage has old earth trip only, 2 consumer units in kitchen cupboard
with seperate metal clad switch to kitchen sockets, wired out back on one consumer unit. 2 6mm T&E feeds to 2 wooden boxed fuse baords with ceramic fuse holders. cables clipped to beams. 2.5 swa run to garage, no earth on armour. loose cables in loft. Cottage is thatched ! I am going to do full survey / test for re wire. Would you put another eatrh rod in for cottage to lower Ze ?




Just re read your reply, Are you suggesting that the eath at garden room is only conected
at new earth rod and not back to cottage ?

That's exactly what i am saying. What you WOULDNT do is connected the earth in summer house to the an earth rod, AND connect this to the house earth through the SWA

 

[Pat Tester]

Many thanks

 

[LukeScotty]

why is this shakey? could you explain why u can't use the earth from the cottage?

 

[Shakey]

why is this shakey? could you explain why u can't use the earth from the cottage?

Lots and lots of reasons Luke.

If it was a TN system, the DNO does not allow you to export the earth out of the equipotential zone. Lets say there is an extraneous conductive path in the shed, garage etc. (perhaps a water pipe)

So you connect the house earth to an MET in the shed, then bond to the extraneous.

And suppose the water pipe picks up a live to earth fault somewhere else, you will now be bringing the earth fault INTO your house. AND onto the DNO's earth system (appreciate this a very simplistic explanation)

with earth rods you have 'step and touch' voltages. So if an earth fault current flows down the rod (to try and get back to the supply) it flows through the ground which has a resistance. Current and resistance? oops, theres ohms law, so you now have a voltage drop. And that voltage will vary over distance because of the grounds resistance. So by giving the shed/summer house its OWN earth, you are creating a mini equipotential zone and 'localizing' any fault problem

With the SWA, by connecting the armour as a CPC at the house end only, you are 'directing' any fault current on the cable back to the house, where you want it to go so the CPD can operate!


this is really quite an in-depth subject, Luke, and worth looking into further. I have got a very good leaflet on it which i will ping to you monday from work (remind me though!!). You may be able to post it up here?

 

[wayne]

shakey this is something im interested in too whats dno?
where can i find more info on this

 

[Shakey]

shakey this is something im interested in too whats dno?
where can i find more info on this

Distribution Network Operator (your lecky supplier!)

I have a very good article on it, i will send it to luke monday, and see if he's allowed to post it on here

 

[wayne]

ahhh! the old LEA
the iee.org has something on this type of thing (sheds /outbuildings) their main concern was two different earth potentials and the pd between them no mention was made of exporting /importing earth ,but im with you importing an earth fault could be dangerous

 

[MacSparky]

I have got a very good leaflet on it which i will ping to you monday from work (remind me though!!). You may be able to post it up here?

Hi shakey, just perusing and found this, i dont suppose you still have a copy of that leaflet?? if you have i sure would appreciate a copy and would gladly ad it here if permitted

 

[Shakey]

Hi shakey, just perusing and found this, i dont suppose you still have a copy of that leaflet?? if you have i sure would appreciate a copy and would gladly ad it here if permitted

hi Mac, yeah still got it in work,

PM me (so i remeber when i log in!) and i will fly it accross to you

 

[rme]

Shakey, any chance I could have a copy of the leaflet?

 

[Guest123]

The thread is nearly 4 years old and shakey is no longer a member.

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