Main Bonding - Multiple Buildings

[snipersmith87]

Could somebody please put me on track.

Main bonding conductors are sized relevant to earthing conductor (TN-S / TT) or PEN conductor (TN-C-S).

On a large installation (Industrial / Commercial) with multiple buildings containing Extraneous parts should ALL the bonding conductors be sized the same throughout according to origin or sized accordingly with supply to that specific building??

 

[westward10]

They should be the same size if using the same source of supply.

 

[snipersmith87]

They should be the same size if using the same source of supply.

So if my main bonding is 35mm at origin building, any Sub mains to seperate buildings will have to be a minimum 35mm?

 

[westward10]

You will require a cpc of at least 35.0 to the separate buildings. If using the armour of a swa cable then it's conductivity will have to equate to the 35.0 copper. If using the armour the cable would have to be at least 240.0, four core.

 

[James]

would you not consider the submain to be the origin of supply to say building B fed from Building A?

i.e. main building A has 400A supply with 35mm earth provided.

from there a board feeds things in same building and has 2 feeds out to other buildings, say 100A each building.

would you not consider the private supply to buildings b & c to require bonding suitable for a 100A supply and its associated disconnect times.

I am not necessarily disagreeing with you @westward10 but was wondering what the thought process and/or associated reg. was?

 

[snipersmith87]

would you not consider the submain to be the origin of supply to say building B fed from Building A?

i.e. main building A has 400A supply with 35mm earth provided.

from there a board feeds things in same building and has 2 feeds out to other buildings, say 100A each building.

would you not consider the private supply to buildings b & c to require bonding suitable for a 100A supply and its associated disconnect times.

I am not necessarily disagreeing with you @westward10 but was wondering what the thought process and/or associated reg. was?

This is where I'm getting confused also

 

[westward10]

Is this TN-C-S.

 

[James]

Is this TN-C-S.

consider it a training exercise, i would like to understand the principals for any type of supply.

 

[snipersmith87]

Is this TN-C-S.

It is Westward...however i too would like to know the principles with each supply. My understanding was more along the line of James.

 

[Ian1981]

If you have one main supply and earthing arrangement then you have only one MET, bonding if pme must take into account the size of the dno PEN conductor and connect to the MET, so all extraneous parts in each building must connect back to the MET so are sized all the same.
In each building from each sub main you will have an earth marshalling terminal, the submain cpc must be large enough to act as a cpc and combined protective bonding conductor.
It is exactly the same principle when people ask about supplies to garages/outhouses and everyone pipes up about any extraneous parts in the building need to be connected to a 10 mm to the house if pme etc etc.

 

[Wilko]

Hi - I think of it as the fault loads must be able to be handled at the furthest point. So as per @Ian1981 no reduction as you go to another board on site.

 

[James]

Thanks guys

 

[snipersmith87]

Thankyou for the replies however I'm still slightly lost... Could someone tell me where my theory is wrong?

If i had a 35mm sub main to a seperate building, why couldn't my main bonding for extraneous parts within that be 10mm and fed from the relevant DB?
As surely this will be adequate enough to limit touch voltage within that specific building as per table 54.8

Also regarding loss of PEN conductor would the fault current not take quickest route back to transformer via earth which would be the main bonds / extraneous parts at origin limiting the fault current further downstream...therefore not needing same size bonding conductors throughout?

 

[dave992]

Thankyou for the replies however I'm still slightly lost... Could someone tell me where my theory is wrong?

If i had a 35mm sub main to a seperate building, why couldn't my main bonding for extraneous parts within that be 10mm and fed from the relevant DB?
As surely this will be adequate enough to limit touch voltage within that specific building as per table 54.8

Also regarding loss of PEN conductor would the fault current not take quickest route back to transformer via earth which would be the main bonds / extraneous parts at origin limiting the fault current further downstream...therefore not needing same size bonding conductors throughout?

Hi buddy. Did anyone provide you with more information and clarification? I would be interesting to know more. Thanks