Metallic pipes and outbuildings!!

[digital_boy]

Morning all.

Couple of questions regarding the 18th in regards to outbuildings with metallic pipes in them, causing very different answers between a few of us in the pub!

Right so. If a metallic pipe enters any building but has an 'insulating section' then it need not be earthed? I do not understand this, on most new builds it comes in with blue alcathene water pipe and then usually out in plastic around the services, by regs do we still need to earth the tap!?

If I was to wire up an outbuilding say with a 3core SWA from the dB 1 in customers house and THERE IS metallic pipe work in there... What is the correct earthing method here, isit take a 3 core and connect a core to the earth bar, earth the armourings (db1) but at the other end do not connect the earth core or the armourings and instead run an earth to a rod from the MET in the new outbuilding board?

On the other hand if no metallic pipe works are present then 3core SWA with armourings connected to met in outbuilding is fine ?

Not my aspect of work but very intrigued

Thanks
DB

 

[cliffed]

If there’s an insulated part entering the premises,no bonding required.(water/gas).
Swa supply,& bonding required, Earth bonding conductor sized correctly,to size of Rec intake.
This May require TT System,if no bonding Swa would be fine,this relates to Tncs.

 

[Leesparkykent]

What you doing in the pub at 6:08AM?

 

[Midwest]

You were need to verify that the metallic pipes in the outbuilding were extraneous or not firstly.

 

[digital_boy]

Ok.... Still not too clear.

If it's a tncs at origin. A new dB in the outhouse with metallic pipe work in there I DO NOT connect the swa CPC / armourings at all and instead TT at the outbuilding?

Thanks all

 

[cliffed]

Ok.... Still not too clear.

If it's a tncs at origin. A new dB in the outhouse with metallic pipe work in there I DO NOT connect the swa CPC / armourings at all and instead TT at the outbuilding?

Thanks all

Yes TT this outbuilding, then earth bonding can comply to regs.
Separate the earthing on the Swa cable,including Swa armouring,so a new Tt system will exist.

 

[Midwest]

This has been talked about numerous times. Have a look in the resources section, there’s a piece in their about the subjects.

Are the metallic pipes extraneous?

 

[radiohead]

Morning all.

Couple of questions regarding the 18th in regards to outbuildings with metallic pipes in them, causing very different answers between a few of us in the pub!

Right so. If a metallic pipe enters any building but has an 'insulating section' then it need not be earthed? I do not understand this, on most new builds it comes in with blue alcathene water pipe and then usually out in plastic around the services, by regs do we still need to earth the tap!?

If I was to wire up an outbuilding say with a 3core SWA from the dB 1 in customers house and THERE IS metallic pipe work in there... What is the correct earthing method here, isit take a 3 core and connect a core to the earth bar, earth the armourings (db1) but at the other end do not connect the earth core or the armourings and instead run an earth to a rod from the MET in the new outbuilding board?

On the other hand if no metallic pipe works are present then 3core SWA with armourings connected to met in outbuilding is fine ?

Not my aspect of work but very intrigued

Thanks
DB

There is no requirement to earth any pipe or tap. There may be a requirement to bond, that is not the same as earthing.
The requirement to bond a metallic service is because it IS at earth potential, not because it isnt.
A metallic service coming into a building is likely to be in contact with the general mass of earth and will therefore introduce an earth potential into the property. In the event of a fault on the electrical installation there may be a rise in potential on conductive (earthed) parts of the installation until the protective device disconnects the supply. Anyone in simultaneous contact with say a kettle and the tap may be subject to a serious shock. By bonding the two (conductive and extraneous parts) together there can be no potential difference and a reduced shock risk.
If the incoming water service is in plastic or has an insulating section close to the point of entry it cannot introduce an earth potential so will not require bonding.
Regarding outbuildings. The requirements depend on the CSA and material of the distribution circuit cpc. As long as it is in copper and meets the minimum CSA for a bonding conductor it can be used as a combined cpc and main bonding conductor. For example if the supply is TNS a 6.0mm cpc would be adequate (for a standard 60/100a service head), but if the supply is TNCS then a minimum bonding requirement of a 10mm copper conductor back to the MET applies. If the outbuilding was served by a 10mm 3 core SWA then that could be used for main bonding, if on the other hand it was served by a 6.0mm then it couldnt, so it would be necessary to separate the TNCS at the outbuilding, install a TT, and bond from that.
Steel wire armouring is generally not compliant as a bonding conductor, so if that is used as a cpc then it could not serve any bonding requirements in the outbuilding.

 

[cliffed]

Well explained,total agreement

 

[davesparks]

Ok.... Still not too clear.

If it's a tncs at origin. A new dB in the outhouse with metallic pipe work in there I DO NOT connect the swa CPC / armourings at all and instead TT at the outbuilding?

Thanks all

Incorrect, if you have a TNCS supply and there are extraneous parts in the outbuilding you EITHER connect main bonding to them from the origin OR you create a seperate TT system and connect main bonding to that.

Main bonding from the origin does not mean running a seperate bond, the CPC of the submain can be the main bond as long as it is big enough. So if the installation requires 10mm main bonding and your 3 core SWA is 10mm or bigger then it can be used and you don't need a seperate TT system.

Sometimes there are other considerations such as if the submain is ridiculously long (hundreds of metres) you may consider adding earth rods.

 

[telectrix]

Incorrect, if you have a TNCS supply and there are extraneous parts in the outbuilding you EITHER connect main bonding to them from the origin OR you create a seperate TT system and connect main bonding to that.

Main bonding from the origin does not mean running a seperate bond, the CPC of the submain can be the main bond as long as it is big enough. So if the installation requires 10mm main bonding and your 3 core SWA is 10mm or bigger then it can be used and you don't need a seperate TT system.

Sometimes there are other considerations such as if the submain is ridiculously long (hundreds of metres) you may consider adding earth rods.

with the proviso that if it's a TNC-S supply and the outbuilding itself is of metal construction, then a TT earthing arrangement must be installed separate from the main earthing system.

 

[Ian1981]

with the proviso that if it's a TNC-S supply and the outbuilding itself is of metal construction, then a TT earthing arrangement must be installed separate from the main earthing system.

Depends if the metal work is introducing a potential and is accessible to touch, building insulated materials like plasterboard and external brickwork may mean that it is not accessible