how to upgrade the earthing conductor?

[eskimo39]

You can even find diagrams on DIY sites now !!!!!! http://www.diynot.com/wiki/electrics:earthing_supply_types_and_bonding:earthing_arrangements unbelievable.

 

[Des 56]

The information is not a secret,but the understanding of the system should be fundamental to any electricianL
limitations are what safety is about, Diyers should limit their work to the level of their understanding
Once they exceed that understanding,any work they carry out could be dangerous
Informing the ignorant of ways to end their existance may not be a sensible action

 

[SimpleSimon]

Going back to a point raised earlier gents.
Are we saying it's acceptable to leave the current earthing as is it and reterminate in a MET and link into the CU with 16mm.
Or
Apply the adiabatic equation and work out if it is acceptable according to this.
I'm with brucelee on this one. Yes the OSG is a guide, hoeever there must be reason behind stating these figures in the first place backed by knowledge and reasoning from the regs.

 

[Deleted member 9648]

That will be a tn-s system and is the suppliers earth to met, so providing you have a ze lower than 0.8 ohms and the consumers earth from the met to the consumer unit is of an adequate size its of no concern to your pir. If on the other hand the small wire is coming straight off the sheath into the consumer unit i usually reterminate into an external met and take a 16mm into the cu it will then satisfy the cert as the consumers main earthing conductor is of the right size. you should neva mess with there incoming cable, if you take a ze reading and it doesnt satisfy you contact the supplier to upgrade hope this may help.

If I was doing a PIR and there was a 6.0mm earth from the cutout to the MET and then a 16mm to the CU,the earth size on the cert would be 6mm, not 16mm.....the 6.0mm will have to carry the same fault current as the 16mm.

 

[SimpleSimon]

Exactly what I was thinking.

 

[Sparky Ninja]

As I've already stated, sizing of protective conductors is by either SELECTION or CALCULATION!!
If it's a new installation then selection can be applied at the design stage. This chap has attended an already existing installation and is thinking about upgrading the earth when it most likely is not necessary.

If you don't know how to do the adiabatic then say so!!!


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[pushrod]

just to come in on this at a late stage on what has obviously been an interesting discussion. It should be remembered that unnecessarily upgrading earths could potentially cause problems in itself as this could lead to higher PEFCs that might exceed the breaking capacity of the protective devices so they can not clear the fault safely. It really should be checked properly and not just immediately assumed that bigger must automatically be better.

 

[telectrix]

just to come in on this at a late stage on what has obviously been an interesting discussion. It should be remembered that unnecessarily upgrading earths could potentially cause problems in itself as this could lead to higher PEFCs that might exceed the breaking capacity of the protective devices so they can not clear the fault safely. It really should be checked properly and not just immediately assumed that bigger must automatically be better.

i may be inaccurate here, but theoretically the protective device, usually a 1361, will blow long before the fault current gets anywhere near it's rated breaking capacity of 16kA. it's a very rare occurence for a fault current to develop upstream of the circuit protective devices, although not unknown.

 

[SimpleSimon]

As I've already stated, sizing of protective conductors is by either SELECTION or CALCULATION!!
If it's a new installation then selection can be applied at the design stage. This chap has attended an already existing installation and is thinking about upgrading the earth when it most likely is not necessary.

If you don't know how to do the adiabatic then say so!!!


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Fair comment.
But selfishly let me take another view.
A few months ago I started a thread similar to this where I went to a customers house.
British gas where to install a new central heating system but refused to do it cause the main earthing conductor was 4mm straight into the MET on a TNS system.
I'm still in the process of awaiting DNO to come out so it can be changed over.
Now although the Ze was fine and PFC I questioned the inadequacy of the size that would it take the fault current. Would this mean I shouldn't be changing this too and telling British Gas to stop being so silly?

 

[Sparky Ninja]

Fair comment.
But selfishly let me take another view.
A few months ago I started a thread similar to this where I went to a customers house.
British gas where to install a new central heating system but refused to do it cause the main earthing conductor was 4mm straight into the MET on a TNS system.
I'm still in the process of awaiting DNO to come out so it can be changed over.
Now although the Ze was fine and PFC I questioned the inadequacy of the size that would it take the fault current. Would this mean I shouldn't be changing this too and telling British Gas to stop being so silly?

It would depend completely on the calculation. I can't say yes or no without knowing more.


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[SimpleSimon]

No no I understand. And I also understand why British Gas weren't happy installing with that behind it and personally I'm happy to upgrade it, also because DNO are going to change it to a PME.

 

[pushrod]

i may be inaccurate here, but theoretically the protective device, usually a 1361, will blow long before the fault current gets anywhere near it's rated breaking capacity of 16kA. it's a very rare occurence for a fault current to develop upstream of the circuit protective devices, although not unknown.

BS 1361s have a breaking capacity of 16.5 or 33kA depending on type. Think you might be thinking of the fact that if you have a CU to BS 5486 or BSEN 60439 then the enclosure is rated to withstand high PFCs and you can then record max short circuit capacity as 16kA if you have a BS1361 or BS88 (less than 100A)
I was just making the point that if someone is thinking "oh i'll upgrade the earthing" without full consideration, especially if they have older style CBs or BS3036s, which certainly won't be in such a CU, then they could be opening a can of worms as their short circuit capacity could well be 1, 2, or 3kA.

Must admit i only glanced thru the thread so don't know the full details as to whether a CU upgrade was being considered as well.