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robo83

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Hi,

Ive been asked to price for a board change in a flat.

I can see the incoming tails are 25mm. It's a PME install and the main fuse is about 50meters away at the end of the block.

The gas/water bonding is 2.5mm which I can access and upgrade to 10mm.

The issue is the earth which comes into the property looks to be a 6mm.

How do I stand about the main earth and not being able to upgrade due to access.?

Robo
 
I assume the supply has a switch fuse protecting it so the earthing conductor is a cpc, this doesn't change the fact it is inadequate to support PME bonding.
No answer to that unless you can create a TT system.
 
I assume the supply has a switch fuse protecting it so the earthing conductor is a cpc, this doesn't change the fact it is inadequate to support PME bonding.
No answer to that unless you can create a TT system.

It's impossible to create TT as is it to upgrade the cpc.

I read another thread where the supply in being a PME fused at 60amp then once it enters the property becomes a Tns due to the cpc being separate.

All I can see at the supply side being a pme L and N. This is the same for the whole block.

Wouldn't the seperate cpc make this install a tns?
 
Your responsibility is to make the flat safer... so by upgrading the CU then this is achieved.

Ring your scheme and see what they suggest..... and let us know what they say.......there are a few sites I've seen where even changing the CU isn't really possible, let alone upgrading the main earth or bonding..
 
If I understand correctly the size of the earthing conductor is set by the DNO neutral size, in your case some 50m away. I don't think anything we have can change that requirement (except TT) as it's to protect the installation against external fault currents. But it's possible DNO's local planning eng. could have useful input ? (I know, I know, the pigs are being readied for takeoff just outside here ...)
 
It's impossible to create TT as is it to upgrade the cpc.

I read another thread where the supply in being a PME fused at 60amp then once it enters the property becomes a Tns due to the cpc being separate.

All I can see at the supply side being a pme L and N. This is the same for the whole block.

Wouldn't the seperate cpc make this install a tns?
No it is TN-C-S however you look at it. You have a nice situation there, no point putting 10.0 bonds in if the supply cpc is 6.0. It is possible you need even bigger bonds than 10.0, the only way to "possibly" avoid this is if there is a common gas and water service to all dwellings which is sufficiently bonded elsewhere. You could then bond to the services in the property using the existing cpc. You would have to be certain the services are metal throughout.
 
Are there multiple DNO supplies and gas water supplies into the Building or one? If there was only one and main bonding was done to MET @ DNO/switch fuse position then just treat as circuit to flat. More info needed tho before confirming this
 
Each flat has seprate fused isolator and meter. About 40 flats, I'm unable to locate any MET within the DNO cupboard.
 
All gas meters come from the same supply, each flat has own meter.

Surly these would be earthed by the DNO, I just can't find the DNO MET.
 
Is that one gas supply bonded? Are there no certs available.. i would hesitate to guess they have been bonded to MET but you should be able to locate them. Treat the sub as a circuit and carry on with your consumer unit change, if you want to bond in flat you may but isnt necessarily req so dont worry about the 6mm cpc supplying flat. What size fuse is in submain switch fuse,
 
All gas meters come from the same supply, each flat has own meter.

Surly these would be earthed by the DNO, I just can't find the DNO MET.
How do know the earthing system then, is there a Ryefield board that could have a combined neutral/earth bar.
 
Is that one gas supply bonded? Are there no certs available.. i would hesitate to guess they have been bonded to MET but you should be able to locate them. Treat the sub as a circuit and carry on with your consumer unit change, if you want to bond in flat you may but isnt necessarily req so dont worry about the 6mm cpc supplying flat. What size fuse is in submain switch fuse,

No certs available, I located the gas meter and this isn't bonded and neither is the gas/water pipping within the flag. There is a 60amp fuse in isolator for each flat in the DNO cupboard.

How do know the earthing system then, is there a Ryefield board that could have a combined neutral/earth bar.

Each flat has a 60amp isolator labeled PME. There is another cupboard which is expect has a Ryefield board inside but this is locked.

Thanks for everyone's help do far.
 
Just wondering if you carried out Ze, best do that 1st and take it from there.
I think you will find it will be within limits.

Ive seen loads of 6mm earths and tested fine and no you can not TT, if you have an issue with the earthing you ring dno.

Good luck
 

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