MAIN EARTH BONDING domestic installation

[piz]

Hello
When we are asked to change a CU i have been told on pme and tns the main earthing conductor is the responsibilty of the electricity board.
so if this is the case why is a 16 mm earth sold on packs of 2meter tails?,
example change board 25mm tails or 16mm if 80amp main fuse 10mm to gas and water but only sometimes 4 or 6 mm main earth do we just record this on an EIC
Cheers

 

[Deservices]

No you should be changing this to 16mm earth. When they say the earth is there responsibility they mean the earth coming in not the earth wire going to the board.

 

[piz]

So from earth comming in say 6mm earth block connected then 16mm from there to the board?

 

[dagrat]

As above, the dno may or may not supply an earth facility but its always up to you to sort one out. You can decide the size of the earth by selection or calculation via the adiabatic equation.

 

[topcat]

DNO only have to provide earth to the instalation not from service head to CU as I understand it.
thats why tails come with earth .

 

[dagrat]

If after contacting the dno they refuse to supply an earth, which does happen, then a tt is the only way.

 

[polo1]

As above, the dno may or may not supply an earth facility but its always up to you to sort one out. You can decide the size of the earth by selection or calculation via the adiabatic equation.

Beat me to it ^^^^^ as the man says!

 

[Deservices]

So from earth comming in say 6mm earth block connected then 16mm from there to the board?

Yes from the earth terminal to the board either 10 or 16 mm depending on tails size but generally i always fit 25 mm tails and 16mm earth.

 

[DurhamSparky]

Who buys packs of 2 meter cables???

That's a screw fix / tool station trick .....

 

[Spazz]

When I do a CU change I always install 16mm or 25mm tails and 16mm earth (25mm for TT).

It is so surprising how many TN-S and TT still have 2mm earths attached.

 

[piz]

CEF special offer

 

[Engineer54]

When I do a CU change I always install 16mm or 25mm tails and 16mm earth (25mm for TT).

It is so surprising how many TN-S and TT still have 2mm earths attached.

Why on earth (excuse the pun) are you installing a 25mm earth conductor from a Rod??

 

[Des 56]

I'm wondering when the thread title will be relevant to the thread

 

[Spazz]

Why on earth (excuse the pun) are you installing a 25mm earth conductor from a Rod??

Because none of the rods around me are buried, they are always exposed and Regs state 25mm for none protected and none buried rods

 

[Spazz]

I'm wondering when the thread title will be relevant to the thread

As said in post 2 - the DNO must supply a suitable earth - if they cant provide one within regs then you must supply a TT rod!
The DNO must only make an earth available (if they can) and it is your job then to ensure the cable between the termination of the DNO and the CU is upto regs

 

[Engineer54]

Because none of the rods around me are buried, they are always exposed and Regs state 25mm for none protected and none buried rods

Pretty pointless exercise then, to have an earth rod that's not buried!! lol!!!

 

[Spazz]

Pretty pointless exercise then, to have an earth rod that's not buried!! lol!!!

I know your taking the **** - its driven into the ground but the top is exposed - therefore not buried and not protected against mechanical protection - regs states 25mm - I cant be bothered to get OSG or BGB out for the Reg number

 

[Spazz]

Burry it it's not hard ! Drill , then get good old lumpy out for that bit your drill won't do!

It is when someone has put a concrete path around it - I have a SDS with a Rod driver attachment but that wont drive it past the concrete

 

[MDJ]

I thought a 4mm2 unprotected and a 2.5mm2 protected ie (in conduit) was adequate for a TT system, I may be wrong again of course.

Mike

 

[Spazz]

I will go get my regs in a bit

 

[spark 68]

I know your taking the **** - its driven into the ground but the top is exposed - therefore not buried and not protected against mechanical protection - regs states 25mm - I cant be bothered to get OSG or BGB out for the Reg number

Nicholas I think you have mis-read the OSG.

it says min 25mm if buried but not protected against corrosion

2.5mm if not buried but protected against corrosion and mechanical damage,
4mm if not protected and not buried

 

[Des 56]

Nick,if the earth conductor is protected against corrosion, its not buried,its not mechanically protected,then 10.0mm is ok

542.3.1

 

[spark 68]

Nick,if the earth conductor is protected against corrosion, its not buried,its not mechanically protected,then 10.0mm is ok

542.3.1

I usually use 10mm Des, seeing as how I carry that size anyway.

 

[sparks1973]

I'm wondering when the thread title will be relevant to the thread

well i think we may struggle there Des....
i mean whats `earth bonding`?...

 

[spark 68]

More to the point, how do you terminate 25mm into a domestic CU ?, unless it get's a 'haircut' (Geordie sparks term LOL)

 

[Engineer54]

Nick,if the earth conductor is protected against corrosion, its not buried,its not mechanically protected,then 10.0mm is ok

542.3.1

More than OK for a domestic installation!! lol!!!

 

[Spazz]

542.3.1:
Protected against corrosion and mechanical = 2.5mm copper
Protected against corrosion and not mechanical = 16mm copper
Not Protected against corrosion and not mechanical = 25mm copper

Most properties in Pembrokeshire with TT are not protected against corrosion or mechanical protection so must be 25mm

To terminate 25mm into a CU is a pain I had to split the cable to 4/3 wires and terminate that way over 2 connections - NAPIT said that was the best way

 

[spark 68]

542.3.1:
Protected against corrosion and mechanical = 2.5mm copper
Protected against corrosion and not mechanical = 16mm copper
Not Protected against corrosion and not mechanical = 25mm copper

Most properties in Pembrokeshire with TT are not protected against corrosion or mechanical protection so must be 25mm

To terminate 25mm into a CU is a pain I had to split the cable to 4/3 wires and terminate that way over 2 connections - NAPIT said that was the best way

That reg refers to the cable being buried directly in the ground, see the extract from the OSG I posted earler

 

[Spazz]

Either way in Pembrokeshire its not possible because all the rods have been concreted to make a path - i will take the trunking idea into consideration next time

 

[spark 68]

see reg 543.1.1 on the next page of the BGB:wink_smile:

 

[Engineer54]

542.3.1:
Protected against corrosion and mechanical = 2.5mm copper
Protected against corrosion and not mechanical = 16mm copper
Not Protected against corrosion and not mechanical = 25mm copper

Most properties in Pembrokeshire with TT are not protected against corrosion or mechanical protection so must be 25mm

To terminate 25mm into a CU is a pain I had to split the cable to 4/3 wires and terminate that way over 2 connections - NAPIT said that was the best way

The PVC sheath is the protection against corrosion. Bare copper conductor is the type of cable not protected against corrosion... I wouldn't use 16mm for a domestic UK TT system with an Ra value hovering around 200 Ohms!! lol!!

 

[Engineer54]

Either way in Pembrokeshire its not possible because all the rods have been concreted to make a path - i will take the trunking idea into consideration next time

Shame they didn't install a concrete earth rod pit on the rod and buried the earth conductor in the path too!! Why not run this cable in a metal of heavy duty PVC conduit between rod and where it enters the house, even better chasing the cable into the path. Surely got to be better than a a cable running across a pathway??

 

[spark 68]

Nicholas I have used a Max csa of 16mm before where there is no alternative (or at least a cheap alternative) but never 25mm on a domestic TT, as I say I usually just use 10mm simply because I carry this size for main bonding purposes anyway.