Outbuilding supplied from TT

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lilman

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Doing PIR remedials. House with TT supply; 100mA main incomer. 10mm T&E feed from 30mA RCD side of split load board appears at outbuilding (used as accomodation) in 10mm 2 core SWA (so obviously a joint under the ground somewhere outside, and armour used as the cpc). The CU in the outbuilding is metal and the SWA is terminated to this. There are water pipes and a metal staircase in the outbuilding.

So presumably I remove the SWA armour from the metal CU, and put in a new earth rod for the outbuilding, connecting water pipes and staircase to this?

Or do I leave as is?

 
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if it's a metal CU and the swa is attached to it, the earth terminal also attached to it then we have successfully exported an earth.

Under an earth fault the current could move from the house down the swa armour and to the outbuilding's earth rod? Could the armour take this? Is it not safer to isolate the earthing totally?

 
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Erm.....

There is also the issue of metal CU on a TT - Think that is contra-regulations???

You may have a point, `pache, but what if the "water pipes" are soft copper, underground, between the buildings? Perhaps we shouldn`t bond them, in that case?

Mind you, if the water pipes ARE soft copper, they belong to the property, not the water supply company. Hence you could use them AS the Earth connection.....

(Devil`s advocate!!!!!)

KME

 

steptoe

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HMMMM,

as the SWA is 10mm the armour will supply the earth no problem, is there good continuity between the armour and cpc of 10mm?

not so sure about the metal CU tho,,, do you want to class this as a different installation? or simply a sub main?

I would think about changing to plastic CU.

I would suspect that the water pipes come from the main building(?) so could therefore just be supplementary bonded. this would raise concerns about disconnecting the armour earth and putting a seperate rod in place....

have you tried a continuity between the water pipes and the exported earth?

would indicate if there is any continuity between the water pipes and supply earth at present, if so, then simply leave as is and supplementary bond the water,(as a good practice measure only, its not strictly required in the 17th regs)

as is, I deffo would NOT put a seperate earth(rod) in place. this is a lot dependant on the water pipes having continuity back to MET though.

HTH, Albert.

 

lilman

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Thanks all - particularly Steptoe.

So leave as is if good continuity exists between water pipe-work in outbuilding and MET in house CU. Replace metal CU though; and re-terminate SWA armour to earth bar in new insulated CU? Am I right?

 

steptoe

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yep, you said it a lot better, and shorter than me!

if you have good continuity between MET in main building and pipework in outhouse then I'd be happy enough to just swap the metal CU for plastic.

you can get some fancy gland nuts for providing an earth from the armour now without requiring all the messing about with banjos on plastic.

and bang in some supplementary bonding just for good measure, a bit of 4mm from the pipework to the CU will be more than OK.

re,member tho, its only MHO, other people may disagree, and its only based on the limited info we can share in cyber world.

 
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you can get some fancy gland nuts for providing an earth from the armour now without requiring all the messing about with banjos on plastic.
Got some - they're good. :)

For what its worth if pipes are linked to MET, then would use earth through SWA - but at the moment I'm peed off with earth rods,cos I seem to keep hitting buried concrete and getting Ra of 250 ohms, so not happy bunny (6 attempts so far) :_| . Will be back with big drill and 5/8ths rods tomorrow ]:)

 

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