Main earth bonding protective conductors

[cliffed]

EICR recently done, Swa sub mains armouring used for cpc & MEBPC.
Installed 40 years ago, water/gas/structural bonding required, these are @ 10mm
Tncs earthing system @ origin which is remote from buildings 120mm tails.
The sub mains vary in sizes from 25mm to 50mm….what’s your thinking on coding,if any

 

[westward10]

What do you think on the situation.
With 120.0 supply conductors what size of main protective bonding is actually required 10.0 sounds undersized and this is relevant when assessing the adequacy of the armour.

 

[timhoward]

As above, it sounds as though the main bonding size relative to PEN size is an issue. I think you need 35 sq mm main bonding. (Table 54.8). C2 for me, as another issue has to happen to become immediately dangerous.

This may help: https://www.askthetrades.co.uk/hosted_images/Armour CSA.pdf
regarding adequacy of the SWA armour size in copper equivalent for cpc and bonding.
You'll see that whether the 25mm is PVC or XLPE becomes pertinent.

Also, remember that calculating required CPC size using adiabatic might solve the problem, subject to whether things need bonding in the sub-main locations. I had one a bit like this once, I ending up TT'ing the outbuildings and introducing plastic water pipes to simplify bonding requirements.

 

[cliffed]

As above, it sounds as though the main bonding size relative to PEN size is an issue. I think you need 35 sq mm main bonding. (Table 54.8). C2 for me, as another issue has to happen to become immediately dangerous.

This may help: https://www.askthetrades.co.uk/hosted_images/Armour CSA.pdf
regarding adequacy of the SWA armour size in copper equivalent for cpc and bonding.
You'll see that whether the 25mm is PVC or XLPE becomes pertinent.

Also, remember that calculating required CPC size using adiabatic might solve the problem, subject to whether things need bonding in the sub-main locations. I had one a bit like this once, I ending up TT'ing the outbuildings and introducing plastic water pipes to simplify bonding requirements.

Agree its never been an issue before, the MEBPC are definitely undersized, there’s no easy fix, for new MEBPC to be installed, it’s all 3p supplies a Rcd TT system maybe optional.

 

[cliffed]

What do you think on the situation.
With 120.0 supply conductors what size of main protective bonding is actually required 10.0 sounds undersized and this is relevant when assessing the adequacy of the armour.

Definitely 35mm required it’s how you actually do it.
They are remote buildings quite a distance away from the DNO intake.

 

[cliffed]

As above, it sounds as though the main bonding size relative to PEN size is an issue. I think you need 35 sq mm main bonding. (Table 54.8). C2 for me, as another issue has to happen to become immediately dangerous.

This may help: https://www.askthetrades.co.uk/hosted_images/Armour CSA.pdf
regarding adequacy of the SWA armour size in copper equivalent for cpc and bonding.
You'll see that whether the 25mm is PVC or XLPE becomes pertinent.

Also, remember that calculating required CPC size using adiabatic might solve the problem, subject to whether things need bonding in the sub-main locations. I had one a bit like this once, I ending up TT'ing the outbuildings and introducing plastic water pipes to simplify bonding requirements.

Once mentioned this to the Niceic he replied it’s been in place & there seems to be no problems relating to the system so why change it.
Which definitely goes against all we know

 

[timhoward]

For me the key detail is whether there are metal pipes running from origin to other buildings.
If there is then TT isn't really an option as even with TT the extraneous conductive parts still need bonding according to the intake's sizing requirements. (at least that is my understanding)
If there's gas doing this, TT used to be a non starter, though I think plastic gas pipe does now exist.

I think you either need to end up insulating the services, having nothing to bond, and proving CPC is ok by calculation, or insulating the services and TT. Either way understanding the services is rather key to finding a solution.

 

[westward10]

If 35.0 bonds are required then your 10.0 bonds are inadequate. For the armour of a swa cable to support a 35.0 bond it needs to be at least 240.0.

 

[LastManOnline]

.. I ended up TT'ing the outbuildings and introducing plastic water pipes to simplify bonding requirements.

I do appreciate hearing this type of commonsense approach to bonding issue,s. It has never felt right in my view to allow the plumber, gas installer or builder to dictate the bonding requirements of an electrical installation.

 

[timhoward]

If 35.0 bonds are required then your 10.0 bonds are inadequate. For the armour of a swa cable to support a 35.0 bond is needs to be at least 240.0.

I'm going to admit to being a little bit confused now. Tin hat going on...
The only way I can arrive at that number is following the non-PME rules with the main bonding needing to be not less than half the cross sectional area of the main earthing conductor, so for a 35.0mm bond main earthing would need to be 70 sq mm copper, and 240 sq mm SWA being the smallest to have 70 (ish) copper equivalent.
I think for this one we need the next paragraph in that reg saying to dive straight to table 54.8 in PME conditions, which is where I got the 35.0 sq mm bond requirement from in the first place, based on the 120 sq mm PEN conductor. So I get 95.0 sq mm XLPE as a minimum unless it's 4 core then 70.0mm is ok.
Apologies if I'm wrong!
In either case the OP is unfortunately stuffed!