TT to TNCS conversion or regs fror earth rod
 

Got a TT installation but the earth rod is in a flower bed that will
shortly be a step to the moved front door surrounded by a block paved drive.

System at present is TT via 2 overhead cables. No obvious earths down
any of the supply posts.

I have asked my supplier whether they will convert to TNC-S and am
awaiting a reply. Can anyone comment on my chances of getting the supply
changed over? EDF Energy area but my supplier is Atlantic Electricity
and Gas.

DIY bit if I have to stick with TT.
The solid porch floor needs re-tiling with another layer of ceramic
tiles on top of existing. To get an earth to an earth rod in a suitable
area it would need to cross the porch.
Can I cut a channel for the earth wire in the floor and lay conduit for
an electrician to use when the rod is moved? If so how deep does it need
to be and does it need to be covered by anything special?
Total run would be about 6 metres. How thick would the cable need to be
so I can get the right conduit.

Thanks as ever for any replies.

TT to TNCS conversion or regs fror earth rod
 

Invisible Man wrote:

I have asked my supplier whether they will convert to TNC-S and am
awaiting a reply. Can anyone comment on my chances of getting the supply
changed over? EDF Energy area but my supplier is Atlantic Electricity
and Gas.

Fairly likely, unless you're in the back of beyond. It might help to
ask for 'PME conversion' rather than TNC-S, although it's exactly the
same thing of course. You may have to pay. With an older TT
installation you'll probably need to add or upgrade the main bonding,
otherwise connection of your earthing conductor to the PME terminal will
be refused.

DIY bit if I have to stick with TT.
The solid porch floor needs re-tiling with another layer of ceramic
tiles on top of existing. To get an earth to an earth rod in a suitable
area it would need to cross the porch.
Can I cut a channel for the earth wire in the floor and lay conduit for
an electrician to use when the rod is moved? If so how deep does it need
to be and does it need to be covered by anything special?

Sounds OK. The earthing conductor to the rod will need to be 16 mm^2 if
it will be buried in the ground once outside. This will easily go
through 20 mm PVC conduit for a a straight run, but you'll need a larger
duct if there are many bends. There's no specific rule for depth in a
solid floor, other than "sufficient to avoid damage due to any
foreseeable disturbance".

--
Andy

TT to TNCS conversion or regs fror earth rod
 

On 25 May, 15:28, Andy Wade wrote:
Invisible Man wrote:
I have asked my supplier whether they will convert to TNC-S and am
awaiting a reply. Can anyone comment on my chances of getting the supply
changed over? EDF Energy area but my supplier is Atlantic Electricity
and Gas.

Fairly likely, unless you're in the back of beyond. *It might help to
ask for 'PME conversion' rather than TNC-S, although it's exactly the
same thing of course. *You may have to pay. *With an older TT
installation you'll probably need to add or upgrade the main bonding,
otherwise connection of your earthing conductor to the PME terminal will
be refused.

DIY bit if I have to stick with TT.
The solid porch floor needs re-tiling with another layer of ceramic
tiles on top of existing. To get an earth to an earth rod in a suitable
area it would need to cross the porch.
Can I cut a channel for the earth wire in the floor and lay conduit for
an electrician to use when the rod is moved? If so how deep does it need
to be and does it need to be covered by anything special?

Sounds OK. *The earthing conductor to the rod will need to be 16 mm^2 if
it will be buried in the ground once outside. *This will easily go
through 20 mm PVC conduit for a a straight run, but you'll need a larger
duct if there are many bends. *There's no specific rule for depth in a
solid floor, other than "sufficient to avoid damage due to any
foreseeable disturbance".

--
Andy

Why on the earth does a TT earth require 16mm^2 cable ? Our own Wiki,
backed up by various other sources of information, indicates that the
ground resistance is in the order of 100 ohms, which gives maximum
fault current of 2.4 amps. Even if the ground resistance is half this
that is still only 5 A, so why the dirty great cable ?

I've found a reference that says that 2.5mm^2 cable has a resistance
of 7mOhms/m, so you would need to have an awful lot of metres of even
that before it has any influence on the total resistance.

Rob

TT to TNCS conversion or regs fror earth rod
 

Andy Wade wrote:
Invisible Man wrote:

I have asked my supplier whether they will convert to TNC-S and am
awaiting a reply. Can anyone comment on my chances of getting the
supply changed over? EDF Energy area but my supplier is Atlantic
Electricity and Gas.

Fairly likely, unless you're in the back of beyond. It might help to
ask for 'PME conversion' rather than TNC-S, although it's exactly the
same thing of course. You may have to pay. With an older TT
installation you'll probably need to add or upgrade the main bonding,
otherwise connection of your earthing conductor to the PME terminal will
be refused.

DIY bit if I have to stick with TT.
The solid porch floor needs re-tiling with another layer of ceramic
tiles on top of existing. To get an earth to an earth rod in a
suitable area it would need to cross the porch.
Can I cut a channel for the earth wire in the floor and lay conduit
for an electrician to use when the rod is moved? If so how deep does
it need to be and does it need to be covered by anything special?

Sounds OK. The earthing conductor to the rod will need to be 16 mm^2 if
it will be buried in the ground once outside. This will easily go
through 20 mm PVC conduit for a a straight run, but you'll need a larger
duct if there are many bends. There's no specific rule for depth in a
solid floor, other than "sufficient to avoid damage due to any
foreseeable disturbance".


Many thanks Andy. We had a new consumer unit and new bonding to the
water and gas earlier in the year.

We are in a village just outside Chelmsford. Most of the village has
underground electricity supplies but our 1960s box was fitted in to the
older area of the village which has overhead cables.

TT to TNCS conversion or regs fror earth rod
 

Rob G coughed up some electrons that declared:

Why on the earth does a TT earth require 16mm^2 cable ? Our own Wiki,
backed up by various other sources of information, indicates that the
ground resistance is in the order of 100 ohms, which gives maximum
fault current of 2.4 amps. Even if the ground resistance is half this
that is still only 5 A, so why the dirty great cable ?

I've found a reference that says that 2.5mm^2 cable has a resistance
of 7mOhms/m, so you would need to have an awful lot of metres of even
that before it has any influence on the total resistance.

Rob

I haven't got my books to hand (down at Bungalow) but you need a certain
minimum size for mechanical robustness, unless the wire is otherwise
protected.

You can't go sticking a bit of 2.5mm2 dangling outside, over the ground and
down a hole to a rod - it's too weedy and liable to get damaged.

The same logic is applied to supplimentary bonding conductors dangling
around pipes, but as my memory is ****e, you'll have to wait until I get my
books or someone else with books/better memory can comment.

From memory 4mm2 or 6mm2 is likely to be the minimum acceptable size
depending, purely from a mechanical POV.

But on the argument regarding resistances I agree completely.

Cheers

Tim

TT to TNCS conversion or regs fror earth rod
 

On earthing conductor size for TT....
See table 4.2, page 29 in the latest OSG
(Cu and Zs not 1ohm)

Buried
Unprotected 25mm2
Protected against corrosion 16mm2
Protected against corrosion and mechanical damage 2.5mm2

Not buried
Unprotected 4mm2
Protected against corrosion 4mm2
Protected against corrosion and mechanical damage 2.5mm2

The values have not changed from 16th to 17th.

Regards
Bruce

TT to TNCS conversion or regs fror earth rod
 

On 25 May, 20:08, "BruceB" wrote:
On earthing conductor size for TT....
See table 4.2, page 29 in the latest OSG
(Cu and Zs not 1ohm)

Buried
* Unprotected *25mm2
* Protected against corrosion *16mm2
* Protected against corrosion and mechanical damage *2.5mm2

Not buried
* Unprotected *4mm2
* Protected against corrosion *4mm2
* Protected against corrosion and mechanical damage *2.5mm2

The values have not changed from 16th to 17th.

Regards
Bruce

Thanks Bruce and Tim - I need to put a secondary TT earth at my garage/
workshop and was a bit gobsmacked about the cable size Andy Wade
mentioned. My house TT earth was installed by the local board aver 30
years and in all likelihoods needs inspection and probable upgrading -
note to self must do this !!

Rob

TT to TNCS conversion or regs fror earth rod
 

Rob G coughed up some electrons that declared:

Thanks Bruce and Tim - I need to put a secondary TT earth at my garage/
workshop and was a bit gobsmacked about the cable size Andy Wade
mentioned. My house TT earth was installed by the local board aver 30
years and in all likelihoods needs inspection and probable upgrading -
note to self must do this !!

Rob

Aye - 16mm2 isn't that bad, being the standard size you'd need for any TN-x
main earthing. If you went for 25mm conduit where necessary (common and
available) and use gentle bends and not many of them, I don't think you'll
have much trouble pulling it through 2-3m worth.

Shorter lengths, 20mm ought to be OK, though I've only pulled 10mm2 thought
that, but no trouble.

Cheers

Tim