Bonding to Existing Earth Rod.

[Spudnik]

Chaps,

Got a little job coming up which involves running bonding to gas and water etc.

Supply was TT, but has recently been made TNCS.

i would like your opinions on running bonding to existing earth rod, rather than back to the DB as it is a LONG way from the incoming supplies.

Personally i dont really want to use the rod, however, if someone can give me an excellent reason why i could use it, i would be much grateful.

Ta.

 

[Mr Mark Sparks]

hello js
cant see how you can use the rod as it will import a different potential earth in to the property
also how did they convert tt to tns wouldnt it normaly convert to tncs

 

[Guest123]

also how did they convert tt to tns wouldnt it normaly convert to tncs

They did convert it to TN-C-S.....have another read mate.


J, doesn't the old rod cable run back to the DB then???

 

[Mr Mark Sparks]

They did convert it to TN-C-S.....have another read mate.


he has changed it with the use of magic to make me look stupid

 

[Deleted member 9648]

Not really sure I understand what you are saying....surely if it's now tncs the earth rod will come out....are you thinking of running the bonding to the earth rod position, and then joining in a block to use the earth rod cable to get back to the DB?

Not too sure how you stand anyway...bonding requirements on tncs systems are pretty strict and if you dont go back to the MET it may get picked up on a future PIR or something.

 

[Des 56]

Leaving the rod + earth in as additional to the Tnc-s, yes
Utilising the rod+earth as a remote met. no

Seems like the long run must be a marathon rather than a sprint

 

[bugsy]

Having thought of all the options I think its time to get the cable reeler out

 

[Jason Smith]

Has the service position been moved, or the DB ?

 

[Deleted member 9648]

Jason...understand what you are suggesting now after reading the other posts.
The purpose of main bonding is to ensure there can be no potential difference between conductive parts ( metallic parts of the electrical installation connected to the earthing system) and extraneous parts (incoming metallic services liable to introduce an earth potential) in the event of an earth fault. It follows then that by bonding the water and gas to an earth rod you are just connecting the intoduced earths (gas and water) to another introduced earth....the rod. Only by connecting the main bonding to the tncs system connecting the conductive parts can the bonding be effective.

Does the earth rod not go back to the MET in 10mm though?....you can extend main bonding by means of a durable compression crimp, would it not be possible to use this cable to get back to the MET and use one continuous 10mm to serve both gas and water?.....a possible option if running a new bond is totally impractical.

 

[Spudnik]

Thanks for all the replies chaps!!

Its in a scout hut and there is now (before i got there) a PME earth for the CU and an earth rod for the gas bonding at the other end of the building.

The existing earth rod was connected to the CU via unsheathed- what looks like- 6mm cable.

The gas is bonded in 6mm to the rod and the water is bonded in 10mm which goes to the CU.

So, i need to change the gas to 10mm and was hoping to avoid running to the new MET as it will be a royal pain to install.

Can anyone see anything wrong with cutting the water bond and crimping in a couple of meters so that i can drop it down to loop on the gas first?

Must admit i would never even consider crimping, however, this looks like my only other option.

 

[Deleted member 9648]

I cant see it being a problem mate...provided you use a copper compression crimp,with perhaps heat shrink over.

 

[Mr Mark Sparks]

or solder i guess

 

[Spudnik]

Thanks again all.

I think ill crimp in a new section to drop down to the gas.

Its all above a suspended ceiling, so ill note it on the cert too.