UK Swa as main earth ?!?

[westward10]

Is there no circuit protection?

 

[DJP1997]

Is there no circuit protection?

Not at the moment… do the solution I have come up with as the customer doesn’t want to run new cable is… 100amp fused switch then run the armoured . Make it off the other end properly and convert all 3 buildings to tt

 

[westward10]

What size main protective bonding is required?

 

[DJP1997]

R

What size main protective bonding is required?

Re done my calves and 16mm I believe… based on 100amp pfc of 658a

 

[westward10]

For main protective bond sizes on a TN-C-S system it is based on the DNO supply neutral not PFC.

 

[DJP1997]

For main protective bond sizes on a TN-C-S system it is based on the DNO supply neutral not PFC.

For main protective bond sizes on a TN-C-S system it is based on the DNO supply neutral not PFC.

The supply is 25mm

 

[westward10]

What is 25.0, the tails from the head?
What size earthing conductor is installed from the head?

 

[timhoward]

I'm making a lot of assumptions, but if 100A is a sufficient max demand total for the 3 properties (eyebrow raised a bit), volt drop is ok, the CPC is sized by calculation for ADS of the switched fuse and you proceed as you suggest to make this distribution circuit TT the far end so each property is not connected to a PME supply....
..then my understanding is that you need to be above half the distribution circuit's calculated CPC size to support bonding within that building.
(I've got concerns that this hasn't been sufficiently planned, you've inherited a mess and someone else's attempts at a plan, along with a customer not wanting to spend money, and it sounds as though a 3ph supply should have been considered.)

 

[westward10]

If it becomes TT the distribution cpc is not relevant.

 

[DJP1997]

What is 25.0, the tails from the head?
What size earthing conductor is installed from the head?

This is what Ive got supply end straight into the swa. Earth is 16mm

 

[DJP1997]

If it becomes TT the distribution cpc is not relevant.

This was why I was thinking TT

This is what Ive got supply end straight into the swa. Earth is 16mm
View attachment 118019

 

[DJP1997]

And this

 

[westward10]

Judging by the supply cable I doubt your main protective bonds need to be above 10.0 and if that cable is 120.0 it's armour will support 10.0.

 

[timhoward]

If it becomes TT the distribution cpc is not relevant.

Obviously it's electrically irrelevant and I'm not trying to pick an argument that flies in the face of common sense....

Thing is, I've never found anything in the regs to specifically say how to size bonding in a separate building that becomes TT at point of entry.
541.1.1 seems to make no distinction for TT, just PME or non-PME, and the line about separate buildings.
Is there another section somewhere that is relevant ? Or is it just one for common sense?
Thanks.

 

[westward10]

You would treat it as a TT installation.