I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing cable do I have to use?



Thanks,

Antonio

Hi,

On Thursday 25 July 2013 21:59 asalcedo wrote in uk.d-i-y:


I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?



As a TT earthing conductor will carry very little current, it comes down to
mechanical protection of the cable. From the IEE/IET OnSite Guide:


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

Not Buried:
Unprotected: 4mm2
Protected against corrsion: 4mm2
Protected against corrosion and mechanical damage: 2.5mm2


How will the conductor be protected betwene the top of the rod (ouside I
presume) and the house wall where it will not be subject to damage?

Cheers,

Tim


--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

Reading this on the web? See:
http://wiki.diyfaq.org.uk/index.php?title=Usenet

Hi Tim,

Thank you again for your help.

I agree with your conclusions and that is what I told my electrician.

He said "regulations 542.3.1 cable not protected mechanical damage must be 16mm2" But I think he did not realize that 542.3.1 applies to buried conductor. So I ordered 10 mm2 to have a bit more mechanical protection without going too big and unsightly.

The earth electrode/s will be placed inside the house, in the garage, near the incoming supply and consumer units. Most likely by a wall. The cable from the earth rod will run along that wall until the consumer unit.

I was going to use cable clips. Is that enough or do I need to use conduit or trunking?

Depending on the success with the earth rod impedances I may need just 2m of earthing cable if one electrode at the ground floor in the garage is enough. Or I may need up to 14m if two electrodes are required (the second electrode would be located at the other extreme of the garage that is excavated at the same level as the basement of the house)

Is 10 mm2 enough in all cases?


Regards,

Antonio

On 25/07/2013 21:59, asalcedo wrote:
I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?

What Tim said... copy of the OSG table information he

http://wiki.diyfaq.org.uk/index.php?...o_your_ear th


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Friday 26 July 2013 10:17 asalcedo wrote in uk.d-i-y:


'Tim Watts[_2_ Wrote:
;3097510']Hi,

On Thursday 25 July 2013 21:59 asalcedo wrote in uk.d-i-y:
-

I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth
rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of
earthing
cable do I have to use?

-

As a TT earthing conductor will carry very little current, it comes down
to
mechanical protection of the cable. From the IEE/IET OnSite Guide:


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

Not Buried:
Unprotected: 4mm2
Protected against corrsion: 4mm2
Protected against corrosion and mechanical damage: 2.5mm2


How will the conductor be protected betwene the top of the rod (ouside I

presume) and the house wall where it will not be subject to damage?

Cheers,

Tim


--
Tim Watts Personal Blog: 'Squiddy's Blog'
(http://squiddy.blog.dionic.net/)

'Coverage Maps | Sensorly' (http://www.sensorly.com/) Crowd mapping of
2G/3G/4G mobile signal coverage

Reading this on the web? See:
'Newsgroup access tips - DIYWiki'
(http://wiki.diyfaq.org.uk/index.php?title=Usenet)

Hi Tim,

Thank you again for your help.

I agree with your conclusions and that is what I told my electrician.

He said "regulations 542.3.1 cable not protected mechanical damage must
be 16mm2" But I think he did not realize that 542.3.1 applies to buried
conductor. So I ordered 10 mm2 to have a bit more mechanical protection
without going too big and unsightly.

The earth electrode/s will be placed inside the house, in the garage,
near the incoming supply and consumer units. Most likely by a wall. The
cable from the earth rod will run along that wall until the consumer
unit.

I was going to use cable clips. Is that enough or do I need to use
conduit or trunking?

Depending on the success with the earth rod impedances I may need just
2m of earthing cable if one electrode at the ground floor in the garage
is enough. Or I may need up to 14m if two electrodes are required (the
second electrode would be located at the other extreme of the garage
that is excavated at the same level as the basement of the house)

Is 10 mm2 enough in all cases?



I would run a piece of 90 degree bend conduit down the wall and 10cm below
floor level. Make a little pit for the earth rod and stick a lid on it -
such lids exist for exactly this purpose and are marked "earth rod".

http://www.tlc-direct.co.uk/Products/MTETC.html

That way the cable and the rod clamp is protected in an environment where
mechanical damage is highly likely and furture sparkies will be able to find
it.


--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

Reading this on the web? See:
http://wiki.diyfaq.org.uk/index.php?title=Usenet

Great.

It is certainly less conspicuous than the plastic inspection pit Plastic Inspection Earth Pit | Screwfix.com

The garage floor has either concrete or stone, I'll see if this smaller terminal cover that you mention can be fit without too much trouble

My electrician still says that 16mm2 is required because my meter tails are 25mm2 and:

"Reg. depends of the live conductor

live 6mm2 earth 6mm2
live 10mm2 earth 10mm2
live 16mm2 earth 16mm2
live 25mm2 earth 16mm2
live 32mm2 earth 16mm2"

I am going to tell him

The size of the meter tails is not very relevant for the earthing conductor.
The size referred in that table above is not that of the meter tails but of the conductors in the system after the consumer unit.

Am I correct? What else can I tell him?

Thanks.

On 25/07/2013 21:59, asalcedo wrote:
I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?

You need to be aware that not having it done by a qualified person may
invalidate your insurance. Also if you come to sell the property you
will probably be asked to certify that all electrical work has been done
by a qualified person. In any case can you really afford to take a risk
with such a safety critical task?


--
Peter Crosland

On 27/07/2013 12:57, asalcedo wrote:

asalcedo;3097718 Wrote:
Great.

It is certainly less conspicuous than the plastic inspection pit
'Plastic Inspection Earth Pit | Screwfix.com'
(http://www.screwfix.com/p/plastic-in...arth-pit/59527)

The garage floor has either concrete or stone, I'll see if this smaller
terminal cover that you mention can be fit without too much trouble

My electrician still says that 16mm2 is required because my meter tails
are 25mm2 and:

"Reg. depends of the live conductor

live 6mm2 earth 6mm2
live 10mm2 earth 10mm2
live 16mm2 earth 16mm2
live 25mm2 earth 16mm2
live 32mm2 earth 16mm2"

Those are figures from Table 4.1, and are correct for TN-S and TN-C-S
supplies. However for TT you need table 4.2.

I am going to tell him

The size of the meter tails is not very relevant for the earthing
conductor.

Well it is - but only in cases were the external earth impedance is less
than an ohm.

The size referred in that table above is not that of the meter tails but
of the conductors in the system after the consumer unit.

The sizes quoted apply to that of the line conductor of the system - so
that will be the tails connecting the main cutout to the meter, thence
the CU.

Am I correct? What else can I tell him?

That you think he might be consulting table 4.1 in the OSG, rather than
4.2 as is appropriate for TT supplies.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 27/07/2013 13:58, Peter Crosland wrote:
On 25/07/2013 21:59, asalcedo wrote:
I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?

You need to be aware that not having it done by a qualified person may
invalidate your insurance.

I have never heard of that argument being used in real life... nor have
I seen any disclaimers in insurance policies. Note also that many
include damage to a house as a result of "accidental" damage, which
would suggest that are not excluding householder cock-ups from allowable
claims.

Also if you come to sell the property you
will probably be asked to certify that all electrical work has been done
by a qualified person.

Correcting faults in earthing and bonding is a non notifiable activity.

There is never a requirement that work be carried out by a "qualified"
person. There may be a requirement that notifiable work be carried out
by a "registered competent person" or that LABC are involved or a third
party inspection is done. (note the last option is new to Part P 2013)

In any case can you really afford to take a risk
with such a safety critical task?

I would say most definitely, far safer to do the work yourself, so that
you know its done to an adequate standard, than rely one someone else
who does not need to live there.

ISTM that the professional electrician in this circumstance has already
demonstrated a lack of familiarity with TT systems.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Saturday 27 July 2013 13:58 Peter Crosland wrote in uk.d-i-y:

On 25/07/2013 21:59, asalcedo wrote:
I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?

You need to be aware that not having it done by a qualified person may
invalidate your insurance. Also if you come to sell the property you
will probably be asked to certify that all electrical work has been done
by a qualified person. In any case can you really afford to take a risk
with such a safety critical task?



I have never seen an insurance policy that says that - have you?
--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

Reading this on the web? See:
http://wiki.diyfaq.org.uk/index.php?title=Usenet

On 2013-07-25, asalcedo wrote:


I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?

Just out of curiosity (maybe I missed something), are you willingly
changing from TN-S to TT, and why would you want TT? Or is the
electricity supplier going to cut off the earth connection?

On 28/07/2013 01:48, Adam Funk wrote:
On 2013-07-25, asalcedo wrote:


I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?

Just out of curiosity (maybe I missed something), are you willingly
changing from TN-S to TT, and why would you want TT? Or is the
electricity supplier going to cut off the earth connection?

From previous threads, he is currently TN-S, but the earth impedance is
37 ohms, and the supplier is refusing to fix it. So its either a case of
nag em anyway until they do, or go TT since that level of Ze with TN-S
is about as much use an ash tray on a motobike.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 2013-07-28, John Rumm wrote:

On 28/07/2013 01:48, Adam Funk wrote:
On 2013-07-25, asalcedo wrote:


I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?

Just out of curiosity (maybe I missed something), are you willingly
changing from TN-S to TT, and why would you want TT? Or is the
electricity supplier going to cut off the earth connection?

From previous threads, he is currently TN-S, but the earth impedance is
37 ohms, and the supplier is refusing to fix it. So its either a case of
nag em anyway until they do, or go TT since that level of Ze with TN-S
is about as much use an ash tray on a motobike.

Oh, now that you mention it, I do remember seeing that a little while
ago, but I hadn't made the connection. (No pun intended.) Thanks.

Am I right in thinking that no-one would want a TT given a choice of
that or TN-S or TN-C-S?

On 27/07/2013 17:43, John Rumm wrote:
On 27/07/2013 13:58, Peter Crosland wrote:
On 25/07/2013 21:59, asalcedo wrote:
I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?

You need to be aware that not having it done by a qualified person may
invalidate your insurance.

I have never heard of that argument being used in real life... nor have
I seen any disclaimers in insurance policies. Note also that many
include damage to a house as a result of "accidental" damage, which
would suggest that are not excluding householder cock-ups from allowable
claims.

Also if you come to sell the property you
will probably be asked to certify that all electrical work has been done
by a qualified person.

Correcting faults in earthing and bonding is a non notifiable activity.

There is never a requirement that work be carried out by a "qualified"
person. There may be a requirement that notifiable work be carried out
by a "registered competent person" or that LABC are involved or a third
party inspection is done. (note the last option is new to Part P 2013)

In any case can you really afford to take a risk
with such a safety critical task?

I would say most definitely, far safer to do the work yourself, so that
you know its done to an adequate standard, than rely one someone else
who does not need to live there.

ISTM that the professional electrician in this circumstance has already
demonstrated a lack of familiarity with TT systems.

Insurance policies invariably include a clause that requires the
policyholder to disclose anything that might, and I stress might, affect
the risk insured. It is a frequent, if not the most common, reason for
claims not being paid.

Changing form one type of earthing to another is not IMHO correcting a
fault therefore I would suggest it is notifiable.

To suggest what happened with a past installation does not mean a
properly qualified person is going to make a worse job in future seems a
specious argument to me but I may have misunderstood what you mean.
Likewise to suggest that just because a professional is not going to
live in premises that they will do a worse job is simply absurd.
--
Peter Crosland

On 27/07/2013 20:44, Tim Watts wrote:
On Saturday 27 July 2013 13:58 Peter Crosland wrote in uk.d-i-y:

On 25/07/2013 21:59, asalcedo wrote:
I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?

You need to be aware that not having it done by a qualified person may
invalidate your insurance. Also if you come to sell the property you
will probably be asked to certify that all electrical work has been done
by a qualified person. In any case can you really afford to take a risk
with such a safety critical task?



I have never seen an insurance policy that says that - have you?

All insurance contracts are classified as ones of "the utmost good
faith". This means that there is an overriding requirement to notify the
insurer of any fact that might affect their perception of the risk. This
imposes a very serious requirement on the insured and it does not have
to be spelt out specifically in the policy wording.


--
Peter Crosland

Adam Funk wrote:
On 2013-07-28, John Rumm wrote:

On 28/07/2013 01:48, Adam Funk wrote:
On 2013-07-25, asalcedo wrote:


I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the
earth rod to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of
earthing cable do I have to use?

Just out of curiosity (maybe I missed something), are you willingly
changing from TN-S to TT, and why would you want TT? Or is the
electricity supplier going to cut off the earth connection?

From previous threads, he is currently TN-S, but the earth
impedance is 37 ohms, and the supplier is refusing to fix it. So its
either a case of nag em anyway until they do, or go TT since that
level of Ze with TN-S is about as much use an ash tray on a motobike.

Oh, now that you mention it, I do remember seeing that a little while
ago, but I hadn't made the connection. (No pun intended.) Thanks.

Am I right in thinking that no-one would want a TT given a choice of
that or TN-S or TN-C-S?

I know someone with a TN-C-S supply that has a TT install. He did have a TT
supply and the REC changed the supply. He kept the installation as TT. He
did however have a good electrical installation and he knows what he is
doing.

TBH as long as the electrical installation is sound it matters not what
sytem you use IMHO.

--
Adam

On 29/07/2013 01:51, Adam Funk wrote:
On 2013-07-28, John Rumm wrote:

On 28/07/2013 01:48, Adam Funk wrote:
On 2013-07-25, asalcedo wrote:


I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of earthing
cable do I have to use?

Just out of curiosity (maybe I missed something), are you willingly
changing from TN-S to TT, and why would you want TT? Or is the
electricity supplier going to cut off the earth connection?

From previous threads, he is currently TN-S, but the earth impedance is
37 ohms, and the supplier is refusing to fix it. So its either a case of
nag em anyway until they do, or go TT since that level of Ze with TN-S
is about as much use an ash tray on a motobike.

Oh, now that you mention it, I do remember seeing that a little while
ago, but I hadn't made the connection. (No pun intended.) Thanks.

Am I right in thinking that no-one would want a TT given a choice of
that or TN-S or TN-C-S?

As a generalisation perhaps, although one might argue that a well
maintained TT system has some advantages over TN-C-S - especially if you
want to connect up outbuildings, and / or run your own generator for
standby purposes.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 29/07/2013 07:24, Peter Crosland wrote:
On 27/07/2013 17:43, John Rumm wrote:

I would say most definitely, far safer to do the work yourself, so that
you know its done to an adequate standard, than rely one someone else
who does not need to live there.

ISTM that the professional electrician in this circumstance has already
demonstrated a lack of familiarity with TT systems.

Insurance policies invariably include a clause that requires the
policyholder to disclose anything that might, and I stress might, affect
the risk insured. It is a frequent, if not the most common, reason for
claims not being paid.

Changing form one type of earthing to another is not IMHO correcting a
fault therefore I would suggest it is notifiable.

It *is* correcting a fault, because he currently has no functioning
earthing system at all - that is a serious fault, and needs rectifying
as a matter of urgency.

Its not notifiable in the part P sense - but I am not sure if you are
suggesting one should notify the insurance company? Personally I can't
see the need since so many home owners would not have any clue about
technical aspects of their supply such as the style of earthing used, it
would seem unreasonable for an insurer to expect to be told should it
change. Its like suggesting that you should notify them if the water
company increases your water pressure.

To suggest what happened with a past installation does not mean a
properly qualified person is going to make a worse job in future seems a
specious argument to me but I may have misunderstood what you mean.

I think you have missed the thrust of my argument. I was not talking
about the past installation, but the comments made by his electrician
who was giving advice on the requirements for the TT system. The advice
he gave, was not applicable to TT installs but was based on guidance for
TN systems. This would suggest to me that he may not have much
experience in this particular area.

Likewise to suggest that just because a professional is not going to
live in premises that they will do a worse job is simply absurd.

Depends on the "professional" obviously. However my point was the
counter one - if its your own place, then you are going to make damn
sure the work is done to a high standard.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 29/07/2013 07:32, Peter Crosland wrote:
On 27/07/2013 20:44, Tim Watts wrote:
On Saturday 27 July 2013 13:58 Peter Crosland wrote in uk.d-i-y:

On 25/07/2013 21:59, asalcedo wrote:
I am changing from TN-S to TT earthing system at home.

I will use an unprotected, non buried, earthing cable from the earth
rod
to the earth block.

No phase conductor in the house is larger than 10mm2

To be in compliance with the regulations, which minimum size of
earthing
cable do I have to use?

You need to be aware that not having it done by a qualified person may
invalidate your insurance. Also if you come to sell the property you
will probably be asked to certify that all electrical work has been done
by a qualified person. In any case can you really afford to take a risk
with such a safety critical task?



I have never seen an insurance policy that says that - have you?

All insurance contracts are classified as ones of "the utmost good
faith". This means that there is an overriding requirement to notify the
insurer of any fact that might affect their perception of the risk. This
imposes a very serious requirement on the insured and it does not have
to be spelt out specifically in the policy wording.


I think that has changed this year.

The Consumer Insurance (Disclosure and Representation) Act 2012 came
into force on 6th April 2013. It removes the duty on consumers to
volunteer ‘material facts’ if not asked.

On 2013-07-29, John Rumm wrote:

On 29/07/2013 01:51, Adam Funk wrote:

Am I right in thinking that no-one would want a TT given a choice of
that or TN-S or TN-C-S?

As a generalisation perhaps, although one might argue that a well
maintained TT system has some advantages over TN-C-S - especially if you
want to connect up outbuildings, and / or run your own generator for
standby purposes.

Interesting point.

On 29/07/2013 07:24, Peter Crosland wrote:

Changing form one type of earthing to another is not IMHO correcting a
fault therefore I would suggest it is notifiable.

Only if you're also changing the consumer unit.

Since the revision of Part P in April the only electrical work that's
notifiable is:

- installation of a new circuit,

- replacement of a consumer unit,

- additions or alterations within the zones of a bath/shower room,

- additions or alterations in a room containing a swimming pool or sauna
heater (regardless of zones).

--
Andy