Hi everbody. I've a couple of issuesregarding my home electrics. The
mains supply is via overhead cable, and so is presumably a TT system.
There is a 63A, 100ma RCCD covering the whole installation, but the
consumer unit is a fuse wire type. There is a additional 30ma RCD
protected circuit which supplies an outside shed/workshop via a 6mm
overhead T&E cable.

First issue is the earthing - as far as I can see the only local
earthing is via a spike connected to the earth by the shed. Since this
is via the T&E cable earth wire, which I measure as about 1mm2, this
looks a little inadequate - my understanding that the earth in a TT
system should be 16mm? I'm very happy to install a new earth
cable/spikes if necessary myself, but presumably this is not really
possible under the new regs?

Secondly, I need to arrange an additional external supply for sewage
treatment plant. About 80W. The simplest way to do this would be via an
RCD protected spur off the downstairs ring. Is this OK, and again, can
I do it myself without falling foul of the new regs?

SR.

On Wed, 04 Jan 2006 23:02:45 +0000, SR wrote:

Hi everbody. I've a couple of issuesregarding my home electrics. The
mains supply is via overhead cable, and so is presumably a TT system.
There is a 63A, 100ma RCCD covering the whole installation, but the
consumer unit is a fuse wire type. There is a additional 30ma RCD
protected circuit which supplies an outside shed/workshop via a 6mm
overhead T&E cable.

First issue is the earthing - as far as I can see the only local
earthing is via a spike connected to the earth by the shed. Since this
is via the T&E cable earth wire, which I measure as about 1mm2, this
looks a little inadequate - my understanding that the earth in a TT
system should be 16mm? I'm very happy to install a new earth
cable/spikes if necessary myself, but presumably this is not really
possible under the new regs?

Secondly, I need to arrange an additional external supply for sewage
treatment plant. About 80W. The simplest way to do this would be via an
RCD protected spur off the downstairs ring. Is this OK, and again, can
I do it myself without falling foul of the new regs?

SR.

Does this help?

http://www.iee.org/publish/wireregs/...s_outdoors.pdf

Examples are a garage and a shed, but does outline acceptable connection
methods to the house circuits.

http://www.iee.org/Publish/WireRegs/...ters/index.cfm

Is the searchable bit - some earthing matters mentioned.

I don't want to answer directly as your TT earthing is totally outside of
my experience.

Yes you can do it all yourself, notify Building Control. There is a
prescribed test for an earth rod. Can be done in theory with a couple of
meters and a car battery plus resistors but the pros have proper test gear
for this.

The testing is particulalry important, because, unlike a new bit of
typical fixed wiring, it is difficult to say "it looks right", ground
conditions are too variable.

You can phone the electricity supply company (the REC, not the billing
company) to confirm what they think your earthing arrangements are.

HTH

Tim

SR wrote:

Hi everbody. I've a couple of issuesregarding my home electrics. The
mains supply is via overhead cable, and so is presumably a TT system.
There is a 63A, 100ma RCCD covering the whole installation, but the
consumer unit is a fuse wire type. There is a additional 30ma RCD
protected circuit which supplies an outside shed/workshop via a 6mm
overhead T&E cable.

First issue is the earthing - as far as I can see the only local
earthing is via a spike connected to the earth by the shed. Since this
is via the T&E cable earth wire, which I measure as about 1mm2, this
looks a little inadequate - my understanding that the earth in a TT
system should be 16mm?

Your earth rod will have far higher resistance than the 1mm wire. You
have an RCD to deal with this limitation of TT systems. 1mm is small,
but wiring a high impedance earth with 16mm would be pretty pointless.
On a new install it would not be done the way yours is, but in the
grand scheme of real life problems I'm not sure it really features in
the top 1000.


I'm very happy to install a new earth
cable/spikes if necessary myself, but presumably this is not really
possible under the new regs?

Secondly, I need to arrange an additional external supply for sewage
treatment plant. About 80W. The simplest way to do this would be via an
RCD protected spur off the downstairs ring. Is this OK,

would work fine.


NT

"SR" wrote in message
...
Hi everbody. I've a couple of issues regarding my home electrics. The
mains supply is via overhead cable, and so is presumably a TT system.

The supply to my house is overhead but
we are TC-N-S (PME). Just because it's
overhead does not necessarily mean it's TT.
The supply co have put a label by my meter
actually saying "PME installation"

Best thing is to contact the supply co and
they will tell you.

Roy

RzB wrote:
"SR" wrote in message
...
Hi everbody. I've a couple of issues regarding my home electrics. The
mains supply is via overhead cable, and so is presumably a TT system.

The supply to my house is overhead but
we are TC-N-S (PME). Just because it's
overhead does not necessarily mean it's TT.
The supply co have put a label by my meter
actually saying "PME installation"

Best thing is to contact the supply co and
they will tell you.

It shouldn't be too difficult to tell by looking at the installation
around the incoming feed, company fuse and meter.

--
Chris Green

In article ,
writes:
It shouldn't be too difficult to tell by looking at the installation
around the incoming feed, company fuse and meter.

The FAQ tells you how...
http://www.diyfaq.org.uk/electrical/...al.html#system

--
Andrew Gabriel

wrote:


Your earth rod will have far higher resistance than the 1mm wire. You
have an RCD to deal with this limitation of TT systems. 1mm is small,
but wiring a high impedance earth with 16mm would be pretty pointless.
On a new install it would not be done the way yours is, but in the
grand scheme of real life problems I'm not sure it really features in
the top 1000.

That would have been my assumption - I calculate 20M of 1mm2 to have a
resistance of less tham an ohm. However, the advice at:
http://www.iee.org/Publish/WireRegs/...s_answered.pdf

says 16mm, so that's what I assume I really should have.

SR

In article .com,
wrote:
Your earth rod will have far higher resistance than the 1mm wire.

Eh? ;-)

--
*Real women don't have hot flashes, they have power surges.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

wrote:
Your earth rod will have far higher resistance than the 1mm wire.

Eh? ;-)

The earth electrode resistance (its "resistance to the general mass of
earth") will be much higher than that of a few metres of 1 mm^2 wire,
yes. (Typically 20 - 200 ohms, depending on the soil conductivity.)

Did you think he meant the resistance of the rod itself?

--
Andy

In article ,
Andy Wade wrote:
Your earth rod will have far higher resistance than the 1mm wire.

Eh? ;-)

The earth electrode resistance (its "resistance to the general mass of
earth") will be much higher than that of a few metres of 1 mm^2 wire,
yes. (Typically 20 - 200 ohms, depending on the soil conductivity.)

Did you think he meant the resistance of the rod itself?

That's what he wrote. ;-)

--
*A bartender is just a pharmacist with a limited inventory.

Dave Plowman London SW
To e-mail, change noise into sound.

On 05 Jan 2006 19:48:33 GMT, in uk.d-i-y
(Andrew Gabriel) wrote:

In article ,
writes:
It shouldn't be too difficult to tell by looking at the installation
around the incoming feed, company fuse and meter.

The FAQ tells you how...
http://www.diyfaq.org.uk/electrical/...al.html#system

Can you elaborate a little on "T The live parts in the system have one
or more direct connections to earth."

Being devil's advocate that implies a rather nasty short-circuit, but
I'm sure that's not what is really meant.

Phil

In article ,
Phil Addison writes:
On 05 Jan 2006 19:48:33 GMT, in uk.d-i-y
(Andrew Gabriel) wrote:

The FAQ tells you how...
http://www.diyfaq.org.uk/electrical/...al.html#system

Can you elaborate a little on "T The live parts in the system have one
or more direct connections to earth."

Being devil's advocate that implies a rather nasty short-circuit, but
I'm sure that's not what is really meant.

Did you see the previous paragraph? ...
"Note that in these descriptions, 'system' includes both the supply
and the installation, and 'live parts' includes the neutral conductor."
These definitions of 'system' and 'live parts' come from the wiring
regs. The actual derivations of all these letters is unfortunately
missing from the wiring regs which is why I thought it particularly
good to explain in the FAQ. The original document on earthing types
was a French standard. TN is Terre Neutre (earthed neutral), IT is
Isolée Terre (insulated from earth), etc.

--
Andrew Gabriel

Phil Addison wrote:

Can you elaborate a little on "T The live parts in the system have one
or more direct connections to earth."

Being devil's advocate that implies a rather nasty short-circuit, but
I'm sure that's not what is really meant.

In that context "live" means "current carrying," and is not the opposite
of neutral, IYSWIM. In wiring-regulations-speak "live conductors"
refers to the current carrying conductors of a circuit, as opposed to
the protective (earth) conductor, and therefore includes the neutral.

In colloquial usage it is common to use "live" to refer to a phase
conductor (sometimes called "line") - but it will usually be clear from
the context what interpretation should be placed on the term "live."

Nevertheless a better description of the first letter "T" might be
something like "indicates that one or more points of the source of
supply is directly earthed."

--
Andy

On 12 Jan 2006 19:33:53 GMT, in uk.d-i-y andrew@a17 (Andrew Gabriel)
wrote:

In article ,
Phil Addison writes:
On 05 Jan 2006 19:48:33 GMT, in uk.d-i-y
(Andrew Gabriel) wrote:

The FAQ tells you how...
http://www.diyfaq.org.uk/electrical/...al.html#system

Can you elaborate a little on "T The live parts in the system have one
or more direct connections to earth."

Being devil's advocate that implies a rather nasty short-circuit, but
I'm sure that's not what is really meant.

Did you see the previous paragraph? ...
"Note that in these descriptions, 'system' includes both the supply
and the installation, and 'live parts' includes the neutral conductor."

Oops must have been in my blind spot, transfixed by that apparently
contradictory definition. It would be nice to see it written out in
plain English avoiding any confusing (for non-professionals)
terminology.

These definitions of 'system' and 'live parts' come from the wiring
regs.

I appreciate that but we don't have to perpetuate it. Maybe quote the
regs definition then explain it in everyday language.

The actual derivations of all these letters is unfortunately
missing from the wiring regs which is why I thought it particularly
good to explain in the FAQ. The original document on earthing types
was a French standard. TN is Terre Neutre (earthed neutral), IT is
Isolée Terre (insulated from earth), etc.

That extra information, the French bit, is very helpful. Code letters
that I can't penetrate give me a mental block.

Phil

Andy Wade wrote:

In that context "live" means "current carrying," and is not the opposite
of neutral, IYSWIM. In wiring-regulations-speak "live conductors"
refers to the current carrying conductors of a circuit, as opposed to
the protective (earth) conductor, and therefore includes the neutral.

So some neutrals are both live and earth at the same time.


NT

On 12 Jan 2006 18:15:04 -0800, wrote:

Andy Wade wrote:

In that context "live" means "current carrying," and is not the opposite
of neutral, IYSWIM. In wiring-regulations-speak "live conductors"
refers to the current carrying conductors of a circuit, as opposed to
the protective (earth) conductor, and therefore includes the neutral.

So some neutrals are both live and earth at the same time.

Hmm, that comment is rather ambiguous and misleading. Depends whether it
was made in wiring-reg-speak or electrical-theory-speak.

As a generalisation, it always used to be the case that for private
installations the neutral conductor may *not* be used for protection
against earth leakage currents (PME) without the express written approval
on an individual basis of one or other Secretary of State - can't remember
which one. I'm assuming that is still the case

--
the dot wanderer at tesco dot net

wrote in message
oups.com...
Andy Wade wrote:

In that context "live" means "current carrying," and is not the opposite
of neutral, IYSWIM. In wiring-regulations-speak "live conductors"
refers to the current carrying conductors of a circuit, as opposed to
the protective (earth) conductor, and therefore includes the neutral.

So some neutrals are both live and earth at the same time.

Not within the Consumers installation - i.e. downstream of the service
cutout

John wrote:

Not within the Consumers installation - i.e. downstream of the service
cutout

This is just playing with words really. When the wiring regs talk about
"the live conductors of a circuit" they mean phase and neutral,
colloquially called live and neutral.

So in that sense the neutral is a live conductor (but not a 'hot'
conductor in the sense that Americans us the word).

--
Andy

The Wanderer wrote:

As a generalisation, it always used to be the case that for private
installations the neutral conductor may *not* be used for protection
against earth leakage currents (PME) without the express written approval
on an individual basis of one or other Secretary of State - can't remember
which one. I'm assuming that is still the case

Yes, it's still expressly forbidden and is an offence. Chapter and
verse follows:

Statutory Instrument 2002 No. 2665
The Electricity Safety, Quality and Continuity Regulations 2002
(http://www.opsi.gov.uk/si/si2002/20022665.htm)

The Secretary of State, in exercise of the powers conferred on her by
sections 29, 30(3) and 60 of the Electricity Act 1989[1], hereby makes
the following Regulations: -

General requirements for connection with earth
----------------------------------------------
8(4) A consumer shall not combine the neutral and protective functions
in a single conductor in his consumer's installation.

Offences
--------
35. [...] and any consumer who fails to comply with regulation 8(4) or
34(2) shall be liable on summary conviction to a fine not
exceeding level 5 on the standard scale.

--
Andy

"Andy Wade" wrote in message
...
John wrote:

Not within the Consumers installation - i.e. downstream of the service
cutout

This is just playing with words really. When the wiring regs talk about
"the live conductors of a circuit" they mean phase and neutral,
colloquially called live and neutral.

Your snipping loses the context of what I wrote. I replied to the comment
that sometimes the neutral wire doubled up as Earth. Nowhere did I say that
Neutral could not be considered a live or current carrying conductor


So in that sense the neutral is a live conductor (but not a 'hot'
conductor in the sense that Americans us the word).

Your point being?

John wrote:

"Andy Wade" wrote in message
...

John wrote:

Not within the Consumers installation - i.e. downstream of the service
cutout

This is just playing with words really. When the wiring regs talk about
"the live conductors of a circuit" they mean phase and neutral,
colloquially called live and neutral.

Your snipping loses the context of what I wrote. I replied to the comment
that sometimes the neutral wire doubled up as Earth. Nowhere did I say that
Neutral could not be considered a live or current carrying conductor

Unsnipped this time then, but I did quote the whole of the sentence you
contributed, and more context is readily available by looking back in
the thread (there can't be many people using unthreaded newsreaders now,
surely?).

So in that sense the neutral is a live conductor (but not a 'hot'
conductor in the sense that Americans us the word).

Your point being?

_The_ point being that I (mis)interpreted NT's remark

So some neutrals are both live and earth at the same time.

to mean that neutral conductors are both live and at earth potential
(earthy) at the same time, whereas you interpreted it to mean some
neutrals are also acting as protective conductors (i.e. they are
'earths' (in TN-C systems) and not just earthy) - and I suspect you were
right and that's what he intended to say. That being the case your
comment was quite appropriate and needs no follow-up, but I, having got
the wrong end of the stick felt the need to re-state the wiring regs
meaning of 'live' - for which apologies, OK?

--
Andy