Exported earth

[binky]

Oh no not again :^O

Right, I have been PIRing a hotel which used to be a farm house and stable block. Supply is T-N-Cs from overhead power lines to original farm house building. Supply to old barn is by 10mm FTE on catenary wire (yeah not good). Now I was thinking of seperating earthing to old barn and TTing this building to avoid exported earth, but I have a problem. Central heating boiler which supplies both buildings via large diameter copper pipes is located in old barn, with pipes buried undeground between buldings. So questions are:-

1/ As both buildings have extensive linked pipework are they then both the same equipotential zone or not? ie do I need to separate barn from house at all????

2/ Do I TT the bleeding lot to avoid issues? (currently my preferred option cos I don't like the idea of linked pipework and different electrical systems)

3/ Do I do something else ( :run )

I am needless to say trying to minimise cost to owner cos he inherited a crock of ****e and various contractors havn't helped by doing shoddy work whilst refurbishing the barn. However, I will not be cutting corners at the expense of safety.

Your opinions please

 

[Badger]

Oh no not again :^O Right, I have been PIRing a hotel which used to be a farm house and stable block. Supply is T-N-Cs from overhead power lines to original farm house building. Supply to old barn is by 10mm FTE on catenary wire (yeah not good). Now I was thinking of seperating earthing to old barn and TTing this building to avoid exported earth, but I have a problem. Central heating boiler which supplies both buildings via large diameter copper pipes is located in old barn, with pipes buried undeground between buldings. So questions are:-

1/ As both buildings have extensive linked pipework are they then both the same equipotential zone or not? ie do I need to separate barn from house at all????

2/ Do I TT the bleeding lot to avoid issues? (currently my preferred option cos I don't like the idea of linked pipework and different electrical systems)

3/ Do I do something else ( :run )

I am needless to say trying to minimise cost to owner cos he inherited a crock of ****e and various contractors havn't helped by doing shoddy work whilst refurbishing the barn. However, I will not be cutting corners at the expense of safety.

Your opinions please

i bet you were thinking f .....king Twin and Earth :^O

why dont you run 16mm armoured from one building to other, and run 10mm earth to boiler to cross bond gas a water in there, connected to the earth and armour of armoured through c/u, then connect c/u to met and bond from c/u to gas and water services in 10mm earth. ???

 

[Chr!s]

1/ As both buildings have extensive linked pipework are they then both the same equipotential zone or not? ie do I need to separate barn from house at all????

Do you have a equipotential zone in the barn? You have a similar scenario where a row of terraced on tncs share metalic services and one of the terraced is tt. Some diverted current may flow in the tt terraced, though they must feel its not an issue as theres no regulation covering it.

2/ Do I TT the bleeding lot to avoid issues? (currently my preferred option cos I don't like the idea of linked pipework and different electrical systems)

Its an option.

3/ Do I do something else

Possibly need more info, can you create a equipotential zone in the barn? are there any extraneous conductive parts, if so are they bonded and to what?

 

[binky]

i bet you were thinking f .....king Twin and Earth :^O

+3 - there is more than 1 FTE run externally to this building, which with the internal runs feed a total of 10 DBs of various sizes, shapes and ages There's only 12 rooms, a kitchen, a bar and utiklity area). I even found a small length of white VIR cable supplying a light - never seen white before. The place is a mess of bodges, add ons and re-arrangements of rooms. Most rooms have electrical supplies from more than on DB (fortunately same phases). External lighting is all FTE except a few bits of SWA where the armoured isn't earthed. The only good thing that I can see is that there is a huge amount of bonding cables, because it has only been added too as works have been done, just wish I knew where they went:slap

 

[SparkyMarky]

Excuse my ignorance but what's FTE?

 

[binky]

Possibly need more info, can you create a equipotential zone in the barn? are there any extraneous conductive parts, if so are they bonded and to what?

This is my main issue, the central heating runs extensively around both buildings and links the 2 buildings aswell so we have extensive extraneous conductive system if you get my drift.

---------- Post Auto-Merged at 20:40 ---------- Previous post was made at 20:39 ----------

Excuse my ignorance but what's FTE?

flat twin and earth

 

[Chr!s]

This is my main issue, the central heating runs extensively around both buildings and links the 2 buildings aswell so we have extensive extraneous conductive system if you get my drift

.Its not to much of an issue, just need bonding as it enter the barn, problem may be, tncs 10mm bonding req, do you have a bonding conductor from the met to the barn?, or a cpc which can be utilized for both?

 

[binky]

I need to replace FTE with SWA so can install earthing as required at same time either by the armour, CPC or sparate earth bond.

 

[Chr!s]

I need to replace FTE with SWA so can install earthing as required at same time either by the armour, CPC or sparate earth bond

Providing theres an equipotential zone in the barn, i see no issue using the tncs, though tts good to, your shout. Is volt drop ok?

 

[binky]

Volt drop is absolutely fine

 

[ianmacd]

You would need to check with DNO about exporting their Earth.

If you TT the barn then you would need to run a 16mm CPC from the Barn's new MET back to the MET in the supply building (reg 542.1.8) if the supply building is still TN-C-S.

Probably easiest to TT the lot as you suggested.

---------- Post Auto-Merged at 22:02 ---------- Previous post was made at 22:00 ----------

You have a similar scenario where a row of terraced on tncs share metalic services and one of the terraced is tt. Some diverted current may flow in the tt terraced, though they must feel its not an issue as theres no regulation covering it.

542.1.8 may apply to this.

 

[Chr!s]

f you TT the barn then you would need to run a 16mm CPC from the Barn's new MET back to the MET in the supply building (reg 542.1.8) if the supply building is still TN-C-S.

If you tt the barn the earth would be divorced, am i misreading

 

[ianmacd]

If you tt the barn the earth would be divorced, am i misreading

Didn't he say there was common pipework?

 

[binky]

Didn't he say there was common pipework?

Very common pipework linked underground so chances are very good earth connection

---------- Post Auto-Merged at 22:46 ---------- Previous post was made at 22:44 ----------

If you tt the barn the earth would be divorced, am i misreading

Yep, which is why it is under consideration, problem is the pipework!

 

[kme]

OK. Sorry for delay, I`ve only just come in.........

In your situation, I`d want to drop the DNO earth, and provide a TT supply in entirety.

Do I assume you only have single phase supply; or are there multiple FTE`s?

That said, "our" hotel has a CHP plant located external to the building; the main building is PME, but we had to TT the outbuilding - irrespective of the pipework issue (which is NOT underground- it travels on basketwork into the building.

KME

 

[Larnacaman]

The whole existing installation is currently PME right?? And you want to get rid of this perfectly good earthing system and replace it with a TT system (and probably a single rod at that) ....Total madness!!!

 

[ADS]

You would need to check with DNO about exporting their Earth. If you TT the barn then you would need to run a 16mm CPC from the Barn's new MET back to the MET in the supply building (reg 542.1.8) if the supply building is still TN-C-S.

Probably easiest to TT the lot as you suggested.

---------- Post Auto-Merged at 22:02 ---------- Previous post was made at 22:00 ----------

542.1.8 may apply to this.

Really, Ian.

And yet every time we've discussed this kind of thing, (and disagreed ha ha), the 'Rod-brigade' insist that if you TT part of the installation, then this becomes a seperate earthing system and you don't connect the MET of the TT install to the MET of the PME supply install..........GN8 also states this

There are two ways of dealing with this kind of situation.

One

You can continue the TN-C-S earth to any and all buildings.

The earth that you run to the buildings would need to meet 'bonding' requirements back to the MET.

The shared metalwork running from building to building would be bonded as it enters each building - this is, after all, what we do with 'extraneous conductive parts'.

In this instance, it is bonded to the EMT of the building that it is entering.

Two

You can, indeed, TT each additional building, (leaving the main building TN-C-S).

You would not connect the two earthing systems together.

You would bond any pipework that enters the building to the MET of the building that it is entering.

.

Go and have a fag now, and wait for the fireworks :^O :^O

 

[steptoe]

Here now!

TNCS on an overhead and no-one has noticed an issue with this?!

Has it been rodded directly outside the building where it enters?

Doubtful.

IMHO, and it prob dont count for much,

Rod the whole install,

TT from the origin,

I really dont understand why none of my other esteemed colleagues hasn't pulled the overhead yet.

 

[Larnacaman]

If this overhead supply is anything like the overhead systems from where i come from, it has been fully PME'd and long before the DNO's came into existence. Ditching that PME supply for a TT system, is just pure Madness....

 

[steptoe]

Sorry Larnacaman, but I.have yet to see an overhead that has been spiked any closer than the pole, to me that is not a proper PME system, especially not as recognised in general practice.

or very safe either IMO.

TT it, then you know what you have, I bet you also rely on the guy down the pub to tell you your brakes are still good cos they worked the last time you needed to do an emergency stop too.