Main Earthing conductor size.

[Paul Willoughby]

I have a TNC-S System (PME) , with a 100A fuse, the main Earthing conductor is 10mm, terminated in an earth block, with main bonding conductors of 10mm.
Tails to consumer unit are 25mm with 16mm earth. The Ze of main Earthing conductor is good.

British gas put an isolator last year and at the time I asked if main earth needed upgrading and they said it was standard size.

I have my part p assessment next week, so wondered If I needed to upgrade to 16mm to satisfy the inspector.

Just checking I have everything covered, thanks for any advice that conforms with BS7671


Thanks

Paul

 

[Jay Sparks]

The adibiatic equation will tell you mate. But if you do need to upgrade the 10mm from the head to the MET, you will probably need the DNO to come and do it.

 

[chilliwilly]

It should be OK as it is, and like Jay says its up to the network operator to upgrade it. The fact that the board has 25mm/16mm means you have gone as far as you can with earthing. Maybe worth noting it on EIC in the comments on existing installation box, if its the niccy that your with they like to see that you know what that box is for.

 

[MDJ]

I have a TNC-S System (PME) , with a 100A fuse, the main Earthing conductor is 10mm, terminated in an earth block, with main bonding conductors of 10mm.
Tails to consumer unit are 25mm with 16mm earth. The Ze of main Earthing conductor is good.

British gas put an isolator last year and at the time I asked if main earth needed upgrading and they said it was standard size.

I have my part p assessment next week, so wondered If I needed to upgrade to 16mm to satisfy the inspector.

Just checking I have everything covered, thanks for any advice that conforms with BS7671


Thanks

Paul

so there is a 16mm2 earth from the DNO block to the Dist board and the DNO supplied a 10mm2 to the block?

 

[Jay Sparks]

so there is a 16mm2 earth from the DNO block to the Dist board and the DNO supplied a 10mm2 to the block?

Thats how I read it Mike.

 

[MDJ]

well fine then, the DNO earth isn't our problem, the assessor will know that, providing the ZE is a decent reading

 

[telectrix]

as above^^^^^

 

[Paul Willoughby]

thanks for reassuring me guys, just trying to tick all the boxes before assessment.

 

[chilliwilly]

Is it your fist one or on going?

 

[Eggster71]

Make sure you put a "safety earth connection" label by the marshalling block mate, they like them!

 

[johnboy6083]

There's absolutely nothing wrong with what you have. It doesn't matter one bit that the earth is the same size as the minimum size of TNC-S main bonding conductor.
you size the earthing conductor to the most onerous condition. The adiabatic would almost certainly give you a smaller conductor than the 10mm anyway.
the OSG is not the only way you should design.

 

[alex kane]

Sorry to 're open' such an old post.

I'm having the same dilemma and want to keep the inspector happy. The only difference with my installation is that the 10mm earth goes directly to the consumer unit from the DNO and the fuse is 60A. Is this kosher?

 

[Octopus]

Sorry to 're open' such an old post.

I'm having the same dilemma and want to keep the inspector happy. The only difference with my installation is that the 10mm earth goes directly to the consumer unit from the DNO and the fuse is 60A. Is this kosher?

What size are the meter tails?

 

[alex kane]

16mm

 

[Octopus]

16mm

Best you review the OSG and BYB

and don't get distracted by the pretty pictures in the OSG as they are misleading....

 

[Wilko]

TNS ?

 

[alex kane]

No, TNC-S. I already have but this is the first time I've seen anything less than 16mm used before. It just threw me off. So am I safe in assuming the inspector will be happy with 10mm?

 

[Wilko]

Are you being assessed on this job? If so, it's important to be able to say why you think the install is ok as is ...

 

[alex kane]

Yes I am. It's my first one for NICEIC. I understand why we have minimum CSA's for Earths but having never seen one this small on a domestic job just threw me off a bit.

 

[Octopus]

Yes I am. It's my first one for NICEIC. I understand why we have minimum CSA's for Earths but having never seen one this small on a domestic job just threw me off a bit.

Its NOT unusual for properties to have a small link to the water pipe, or worse, no earth at all.....