seperate bonding conductor

[ianphilip007]

hi

when running a 10mm bonding( seperate to the cpc proctected distribution circuit) conductor for a pme supply to a detached garage that contains (water/gas services) is it ok to run from exisitng house cu to gargae cu and then bond the services to garage cu. or does the bonding conductor have to be unbroken all the way back to the house cu

many thnaks

 

[Deleted member 26818]

Yes technically you should first contact the DNO before exporting PME.
However in practice, it's a complete waste your time.
The DNO connot refuse to allow you to extend the PME, without good cause.
The DNO would be hard pressed to justify their refusal, if the work complies with BS7671.

 

[Edd]

You cant export the earth on pme if there is water or gas services in the outbuilding unless you have permission from the energy supplier.
You would install a rod then bond from outbuilding consumer unit
Terminate exported cpc at garage end in plastic enclosure so that the two earthing systems are totally seperate

Thats how I would do it, I hate the Idea of Extending TNT (PME) earthing outside..(makes me shiver when i see hot tubs on PME) but thats just me because ive seen lost neutrals before!! not nice seeing the whole instalation live compared to the mud outside!
but this arguments been done to death.. as its been mentioned there is a sticky thread somewhere on this

 

[ses]

Agreed

 

[Engineer54]

Thats how I would do it, I hate the Idea of Extending TNT (PME) earthing outside..(makes me shiver when i see hot tubs on PME) but thats just me because ive seen lost neutrals before!! not nice seeing the whole instalation live compared to the mud outside!
but this arguments been done to death.. as its been mentioned there is a sticky thread somewhere on this

You must be one of the very, very few that has!! lol!!!

 

[GLENNSPARK]

nowt wrong with exporting PME....of course there are certain things...such as hottubs....that you would rod....but come on....whats this thing about exporting a good, reliable earthing arrangement where low impedences are easily acheaved..?...

 

[Engineer54]

wouldn't use the armour for the cpc or main bonding conductor. would use either separate 10mm main bonding conductor or use the cpc (3rd core of the swa if 10mm or above) The armour wouldn't have the required csa necessary

I would have absolutely No Problem with using the SWA as my CPC and a 3rd core (10mm and over) as my bonding conductor. SWA CSA will generally comply with CPC requirements up to 95mm in both PVC/XLPE insulated cables (unless of excessive length) from 2 core to 4 core configured cables.

Another point to consider, ...when taking a bonding conductor to an outbuilding or whatever, you are effectively ''Extending'' the equipotential zone, NOT Exporting it!!

 

[Edd]

You must be one of the very, very few that has!! lol!!!

Im sure we have had this conversation before!! and as i said before.. it only takes one lost neutral to kill someone.. stepping out the hot tub! i would prefer a crappy stake and a tingle if there was a fault, than 230v going up me leg!! I prefer the fact that it would take a few faults to ocour to get a dangrous touch voltage with a TT than the single fault with exported PME.. but thats my EXPERIANCE when ive seen flexy hoses blown out under sinks etc but as previously stated its been argued before

 

[GLENNSPARK]

Im sure we have had this conversation before!! and as i said before.. it only takes one lost neutral to kill someone.. stepping out the hot tub! i would prefer a crappy stake and a tingle if there was a fault, than 230v going up me leg!! I prefer the fact that it would take a few faults to ocour to get a dangrous touch voltage with a TT than the single fault with exported PME.. but thats my EXPERIANCE when ive seen flexy hoses blown out under sinks etc but as previously stated its been argued before

well you could always quickly withdraw said leg back into hottub....there! Problem solved!....

 

[ses]

I know which way id rather do it

 

[ianphilip007]

if you were using swa 3core 10mm or above wouldnt the 3rd core be used as a combined cpc/bonding conductor ??

i also agree the armour could be used as either cpc or bonding conductor if csa is adaquate, i just prefer to use the extra core or a seperate bonding conductor.

totally agree with your point re extending the equipotential zone if you provide a suitblly sized bonding conductor back to MET.

the number of people who just want to bang in a rod and replace a low resistance earth path with a relatively high resistance rod when not needed is staggering. the actual circumstances of the installation dont seem to be beeing assessed. just because its PME doesnt mean it has to be TT at the outbuilding. Exporting a pme supply under the right circumstances is not dangerous, extending the equipotential zone via bonding conductor is not dangerous, you just have to assess the installation and use your common sense and knowledge as to which earthing arrangement is required.

 

[Engineer54]

well you could always quickly withdraw said leg back into hottub....there! Problem solved!....

Hear-say scaremongers Glenn, i'd take it all with a pinch of salt!! lol!!

 

[ianphilip007]

i just dont agree with people stating that exporting/extending pme is dangerous or not allowed. the hot tub example shows each installation must be assessed, and the earthing arrangement selected accordingly. As long as the main equipotential zone is extended to include the outbuiding/garage/shed in the event of a lost neutral a dangerous potential should not arrise. surely that the whole point of extending the equipotential zone to include the outbuilding

 

[ianphilip007]

Im sure we have had this conversation before!! and as i said before.. it only takes one lost neutral to kill someone.. stepping out the hot tub! i would prefer a crappy stake and a tingle if there was a fault, than 230v going up me leg!! I prefer the fact that it would take a few faults to ocour to get a dangrous touch voltage with a TT than the single fault with exported PME.. but thats my EXPERIANCE when ive seen flexy hoses blown out under sinks etc but as previously stated its been argued before

was said hot tub effectively bonded back to the MET ? (equipotential zone extended) or had the pme earth just been exported. Just wondered big difference between exporting/extending zone.

for this installation a local earth rod, inrelation to the hot tub would make perfect sense. especially if the hot tub was located on open ground.

 

[Edd]

The hot tub Was an example Ive exported PME to out buildings and have no problems doing so,, as long as the risks are known. But having seen the mess that can be caused by a lost neutral, im just a little wary.As said above a PME supply to a hot tub with an external stake makes good sence. BUT how many people have installed hot tubs without the extra safty feature? oh and remember the RCD wont save you as it wont be unbalanced
PME is a good CHEAP for the DNO earthing system, but people should know the risks. long live TNS

 

[ianphilip007]

i agree tncs does have it problems but how many times does the dno loose the nuetral?? i guess its a case of making sure in the event of a lost neutral the ground and any extrenuous conductive parts are kept at the same potential to limit the risk of electric shock. this can be acheived by effective bonding or by using a seperate earth rod. in my expieirence with pme it comes down to weather it is more cost effective to install a earth electrode or extend the main bonding. if thers no extrenuous conductive parts then just export the earth as you would with a tns system.