A couple of weeks ago I asked for advice about the wiring in my
daughter's new flat under the thread "Improving an old electrical
installation". There was some helpful advice, but it all got rather
buried in a discussion about the relative merits of voltage-operated
trips and RCDs.

Thus when I followed up with more information and questions on 23 June,
I guess some of those who could have offered advice were no longer
following the thread. Would anyone care to revisit it, please, or would
it be better netiquette to repeat my last questions under this new
thread?


--
Kevin Poole
**Use current month and year to reply (e.g. )***
Car Transport by Tiltbed Trailer - based near Derby

Autolycus wrote:
A couple of weeks ago I asked for advice about the wiring in my
daughter's new flat under the thread "Improving an old electrical
installation". There was some helpful advice, but it all got rather
buried in a discussion about the relative merits of voltage-operated
trips and RCDs.

Thus when I followed up with more information and questions on 23 June,
I guess some of those who could have offered advice were no longer
following the thread. Would anyone care to revisit it, please, or would
it be better netiquette to repeat my last questions under this new
thread?


IMHO(&E) on usenet you're better to break down your problem into a
logical order of questions & post them one by one, that way your thread
isn't so easily waylaid or hijacked & you tend to get each aspect
sorted out properly before moving onto the next.

HTH


The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
http://www.diybanter.com

Autolycus wrote:

A couple of weeks ago I asked for advice about the wiring in my
daughter's new flat under the thread "Improving an old electrical
installation". There was some helpful advice, but it all got rather
buried in a discussion about the relative merits of voltage-operated
trips and RCDs.

Thus when I followed up with more information and questions on 23 June,
I guess some of those who could have offered advice were no longer
following the thread. Would anyone care to revisit it, please, or would
it be better netiquette to repeat my last questions under this new thread?

OK, I have copied the new info and posted below... Might as well carry
on here!

Thanks again, to Chipmunk and Andrew especially, and apologies for
starting another NT v the rest thread.

I've had another look at the setup. The incoming supply is he

http://www.mainbeam.f2s.com/flat/incomer.jpg

A tad confusing, but I can't see any earth wires connected into the head
end fuse block...

(Most TN-C-S (PME) setups I have seen would have an earth wire vanish
into the neutral connector block right next to where you have the two
neutrals exit currently)

with a closeup of the earth terminal he

http://www.mainbeam.f2s.com/flat/earth.jpg

Have you got a picture with a slightly wider field of view so we can see
the whole layout?

That earth connector does not seem to be attached to anything other than
the two wires? Is it just resting against the side of the box, or
actually connected to it in some way?

It is indeed next to the incoming neutral. There is also what appears to

Next to is not the same as connected to though...

be a covered flat strip emerging from the incoming cable sheath
immediately below the box and entering it just in front of the main
cable. One the two 16mm2 cables is connected to the upstairs flat's
installation, and the other goes to an earth block with connections to
the equipotential bonding of the incoming gas pipes. A smaller cable disappears
under the floor.

So it's looking like a TN C-S setup?

Not convinced personally (depends a bit on that terminal - but even if
it is attached to the box it could still be a TN-S setup with the
description you give of the flat tab on the cable sheath).

The isolator which is adjacent to the incomer and the Chilton VO trip contains
a 60A fuse, which gives me some comfort about the 16mm2 T&E to the CU.

16mm^2 is indeed adequate for a 60A main fuse

I'm still minded to replace the CU with a split-load unit (Volex from Screwfix
Or GE from Toolstation - opinions?), and to connect all the green or

Not used either, so can't comment. Used a few contactum ones from TLC
recently, which while a bit "plasticy" do have plenty of space to work
with.

green/yellow cables at the incomer/meter board together, with a beefed-up
cable linking the "earth" of the 16mm T&E directly to the other earths
rather than via the trip.

Could do...

Am I right that it does not matter if one of the untraced green
cables does indeed go to an earth rod under the floor?

It matters in the sense that if it does, and that is your only earth
(i.e. you have a TT supply) then you will need RCD protection for all
circuits - not just the usual suspects.

Since the earth trip will then be redundant, would it be better to
remove it completely and replace it either with a Henley block or
a 100mA time-delayed RCD in an enclosure? I'd prefer to avoid new tails,
as even I don't reckon to break meter seals.

Probably better to remove it when not required. Are the tails into it
long enough to reach to the new CU position? If so that saves you a join.

If you decide you do have a TT setup then that may be a good place to
stick a 100mA RCD - but the time delay ones are much more pricey than
the ordinary ones. It may be more cost effective to have a Henley there
and feed two CUs, one with an "ordinary" 100mA RCD and the other with a
30mA one.

One for the rogues gallery: the isolator has a bit of length of 0.5mm2
three-core flex poked into its output terminals to feed the
bell transformer

http://www.mainbeam.f2s.com/flat/transformerflex.jpg

Nice ;-) You can almost here the sound of some very large concepts
flying well above the head of the person who installed that!

Dunno what to do with that - the ring main is yards away.

Since you are changing the CU you could even go for a nice DIN rail
mounting transformer - you would just need a cable run to the bell then
with no extra external transformer.


--
Cheers,

John.

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

"John Rumm" wrote in message
...
Autolycus wrote:


SNIP


I've had another look at the setup. The incoming supply is he

http://www.mainbeam.f2s.com/flat/incomer.jpg

A tad confusing, but I can't see any earth wires connected into the head
end fuse block...

(Most TN-C-S (PME) setups I have seen would have an earth wire vanish into
the neutral connector block right next to where you have the two neutrals
exit currently)

with a closeup of the earth terminal he

http://www.mainbeam.f2s.com/flat/earth.jpg

Have you got a picture with a slightly wider field of view so we can see
the whole layout?

That earth connector does not seem to be attached to anything other than
the two wires? Is it just resting against the side of the box, or actually
connected to it in some way?

The service units I am familiar with have the earth block as shown which is
actually an extension of an internal copper bar link straight off the
neutral connector inside the plastic of the unit

It is indeed next to the incoming neutral. There is also what appears to

Next to is not the same as connected to though...


see above

be a covered flat strip emerging from the incoming cable sheath
immediately below the box and entering it just in front of the main
cable.


That is slightly confusing as it could be an extension of the cable sheath
and may point to a TN-S system although the mounted earth block on your phot
suggests TN-C-S

One the two 16mm2 cables is connected to the upstairs flat's
installation, and the other goes to an earth block with connections to
the equipotential bonding of the incoming gas pipes. A smaller cable
disappears
under the floor.

So it's looking like a TN C-S setup?

Not convinced personally (depends a bit on that terminal - but even if it
is attached to the box it could still be a TN-S setup with the description
you give of the flat tab on the cable sheath).

I'd very strongly suggest you investigate further, hiring an ELI tester if
you have not access to one. It might be possible to use a low ohms meter to
find out if the unit earth block is actually a sheath earth (block to sheath
no voltage present, practically zero ohms) or is as suspected a neutral
coupling (small voltage possibly present block to sheath and a slightly
higher resistance if your gear can measure with a voltage present,
practically zero ohms block to neutral). (Switch off all offtakes then
remove the wires to avoid false path readings. Restore correctly on
completion!) If you are not fully competent get someone in who is. Use fused
test probes

"John" wrote in message
...

"John Rumm" wrote in message
...
Autolycus wrote:


SNIP


I've had another look at the setup. The incoming supply is he

http://www.mainbeam.f2s.com/flat/incomer.jpg

A tad confusing, but I can't see any earth wires connected into the
head end fuse block...

(Most TN-C-S (PME) setups I have seen would have an earth wire vanish
into the neutral connector block right next to where you have the two
neutrals exit currently)

with a closeup of the earth terminal he

http://www.mainbeam.f2s.com/flat/earth.jpg

Have you got a picture with a slightly wider field of view so we can
see the whole layout?

That earth connector does not seem to be attached to anything other
than the two wires? Is it just resting against the side of the box,
or actually connected to it in some way?

The service units I am familiar with have the earth block as shown
which is actually an extension of an internal copper bar link straight
off the neutral connector inside the plastic of the unit

It is indeed next to the incoming neutral. There is also what
appears to

Next to is not the same as connected to though...


see above

be a covered flat strip emerging from the incoming cable sheath
immediately below the box and entering it just in front of the main
cable.


That is slightly confusing as it could be an extension of the cable
sheath and may point to a TN-S system although the mounted earth block
on your phot suggests TN-C-S

One the two 16mm2 cables is connected to the upstairs flat's
installation, and the other goes to an earth block with connections
to the equipotential bonding of the incoming gas pipes. A smaller
cable disappears
under the floor.

So it's looking like a TN C-S setup?

Not convinced personally (depends a bit on that terminal - but even
if it is attached to the box it could still be a TN-S setup with the
description you give of the flat tab on the cable sheath).

I'd very strongly suggest you investigate further, hiring an ELI
tester if you have not access to one. It might be possible to use a
low ohms meter to find out if the unit earth block is actually a
sheath earth (block to sheath no voltage present, practically zero
ohms) or is as suspected a neutral coupling (small voltage possibly
present block to sheath and a slightly higher resistance if your gear
can measure with a voltage present, practically zero ohms block to
neutral). (Switch off all offtakes then remove the wires to avoid
false path readings. Restore correctly on completion!) If you are not
fully competent get someone in who is. Use fused test probes

Thanks for the suggestions: I can easily enough check some voltages with
my DMM, but anything more subtle would require liaison with the many
inhabitants of the upstairs flat before turning off their supply, and
may not be so easy. I'm looking into buying most or all of the required
Part P test instruments - if only so that I don't get caught looking
daft by a professional test. I'd always sooner spend money on tools
than someone else's services.


--
Kevin Poole
**Use current month and year to reply (e.g. )***
Car Transport by Tiltbed Trailer - based near Derby

John wrote:

The service units I am familiar with have the earth block as shown which is
actually an extension of an internal copper bar link straight off the
neutral connector inside the plastic of the unit

Ah, OK. I had not seen one like in the picture before (I guess the
different electricity companies have different "pet" brands they use and
hence you will get different things in different parts of the country)

That is slightly confusing as it could be an extension of the cable sheath
and may point to a TN-S system although the mounted earth block on your phot
suggests TN-C-S

Yup, that is what occured to me as well.

I'd very strongly suggest you investigate further, hiring an ELI tester if
you have not access to one. It might be possible to use a low ohms meter to
find out if the unit earth block is actually a sheath earth (block to sheath

He could also possibly simply measure the voltage between earth and
neutral. On PME it ought to be zero (close to the bond anyway), on TN-S
is may be a small voltage.


--
Cheers,

John.

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

John Rumm wrote:
One for the rogues gallery: the isolator has a bit of length of 0.5mm2
three-core flex poked into its output terminals to feed the
bell transformer
http://www.mainbeam.f2s.com/flat/transformerflex.jpg
Nice ;-) You can almost here the sound of some very large concepts
flying well above the head of the person who installed that!
Since you are changing the CU you could even go for a nice DIN rail
mounting transformer - you would just need a cable run to the bell then
with no extra external transformer.

The low-voltage cable run inside the CU must be insulated or sleeved to
240V - most bell wire is only rated up to 60V.

If it's flats, the opportunity might be taken to upgrade to entry
intercom and emergency lighting on the stairs.

Owain

"Owain" wrote in message
...

If it's flats, the opportunity might be taken to upgrade to entry
intercom and emergency lighting on the stairs.

I'm working on her about an entry intercom or camera, having pointed out
that there's not much point in having a door chain on her inner "front
door" if she's had to go through it into a small entrance hall to open
the outer door to a caller who's rung the bell.

Fortunately the stairs are entirely part of the upstairs flat, so that's
one worry I don't have.


--
Kevin Poole
**Use current month and year to reply (e.g. )***
Car Transport by Tiltbed Trailer - based near Derby

In message ,
Owain wrote:

John Rumm wrote:
One for the rogues gallery: the isolator has a bit of length of 0.5mm2
three-core flex poked into its output terminals to feed the
bell transformer
http://www.mainbeam.f2s.com/flat/transformerflex.jpg
Nice ;-) You can almost here the sound of some very large concepts
flying well above the head of the person who installed that!
Since you are changing the CU you could even go for a nice DIN rail
mounting transformer - you would just need a cable run to the bell then
with no extra external transformer.

The low-voltage cable run inside the CU must be insulated or sleeved to
240V - most bell wire is only rated up to 60V.

There's the additional problem that the transformer will still need to
be supplied via an MCB and so some judicious cutting of the busbar is
likely to be required. Also it'll be 2 units wide which reduces the
space available for circuit MCBs.

Hwyl!

M.


--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Answers: $1, Short: $5, Correct: $25, dumb looks are still free.

"John Rumm" wrote in message
...
Autolycus wrote:

that he was restarting an older thread

OK, I have copied the new info and posted below... Might as well carry
on here!

snip

I've had another look at the setup. The incoming supply is he

http://www.mainbeam.f2s.com/flat/incomer.jpg

A tad confusing, but I can't see any earth wires connected into the
head end fuse block...

(Most TN-C-S (PME) setups I have seen would have an earth wire vanish
into the neutral connector block right next to where you have the two
neutrals exit currently)

with a closeup of the earth terminal he

http://www.mainbeam.f2s.com/flat/earth.jpg

Have you got a picture with a slightly wider field of view so we can
see the whole layout?

No, sorry: wider views get very messy because so many of the bits relate
to the upstairs flat.

That earth connector does not seem to be attached to anything other
than the two wires? Is it just resting against the side of the box, or
actually connected to it in some way?

It's connected to the box, though without delving rather deeper in than
3-phase boxes encourage, I can't tell whether it's electrically as well
as mechanically connected - I assume so.


It is indeed next to the incoming neutral. There is also what appears
to

Next to is not the same as connected to though...

True.

be a covered flat strip emerging from the incoming cable sheath
immediately below the box and entering it just in front of the main
cable. One the two 16mm2 cables is connected to the upstairs flat's
installation, and the other goes to an earth block with connections
to the equipotential bonding of the incoming gas pipes. A smaller
cable disappears
under the floor.

So it's looking like a TN C-S setup?

Not convinced personally (depends a bit on that terminal - but even if
it is attached to the box it could still be a TN-S setup with the
description you give of the flat tab on the cable sheath).

No, I'm not convinced. I wonder if the supply company would have a
record?


The isolator which is adjacent to the incomer and the Chilton VO trip
contains a 60A fuse, which gives me some comfort about the 16mm2 T&E
to the CU.

16mm^2 is indeed adequate for a 60A main fuse

I'm still minded to replace the CU with a split-load unit (Volex from
Screwfix Or GE from Toolstation - opinions?), and to connect all the
green or

Not used either, so can't comment. Used a few contactum ones from TLC
recently, which while a bit "plasticy" do have plenty of space to work
with.

green/yellow cables at the incomer/meter board together, with a
beefed-up
cable linking the "earth" of the 16mm T&E directly to the other
earths
rather than via the trip.

Could do...

Am I right that it does not matter if one of the untraced green
cables does indeed go to an earth rod under the floor?

It matters in the sense that if it does, and that is your only earth
(i.e. you have a TT supply) then you will need RCD protection for all
circuits - not just the usual suspects.

I think it a fair assumption that the connection on the side of the
service head is genuinely earthed, either via the cable sheath or the
Neutral: the upstairs flat has obviously been rewired relatively
recently, and has no other earth connection



Since the earth trip will then be redundant, would it be better to
remove it completely and replace it either with a Henley block or
a 100mA time-delayed RCD in an enclosure? I'd prefer to avoid new
tails, as even I don't reckon to break meter seals.

Probably better to remove it when not required. Are the tails into it
long enough to reach to the new CU position? If so that saves you a
join.

The CU itself is 6 or 7 yards away, inside the flat: the meters etc are
in a shared access hallway. The tails that would need to stretch are
the ones from the meter to the VO trip at present, which would need to
go straight into the 60A switchfuse - but I don't think they're long
enough.


If you decide you do have a TT setup then that may be a good place to
stick a 100mA RCD - but the time delay ones are much more pricey than
the ordinary ones. It may be more cost effective to have a Henley
there and feed two CUs, one with an "ordinary" 100mA RCD and the other
with a 30mA one.

Can one reconfigure split-load CUs so that they have two RCDs, instead
of one plus an isolator? Without wishing to bring heavens or posters
with firm views crashing down on me, I've been running an entirely RCD
protected house (2 separate CUs) for well over 15 years with no nuisance
tripping, and lighting circuits split between the two to ensure nowhere
blacks out completely with just one fault. Otherwise it would need a
second Henley near two new small CUs.


One for the rogues gallery: the isolator has a bit of 0.5mm2
three-core flex poked into its output terminals to feed the
bell transformer

http://www.mainbeam.f2s.com/flat/transformerflex.jpg

Nice ;-) You can almost here the sound of some very large concepts
flying well above the head of the person who installed that!

Dunno what to do with that - the ring main is yards away.

Since you are changing the CU you could even go for a nice DIN rail
mounting transformer - you would just need a cable run to the bell
then with no extra external transformer.

As I said, the CU is some way away so we'd be into floorboard lifting
territory, which may not be ideal in the present circumstances. If I
put a whole-flat 100mA time delayed RCD in a 3 or 4-module box next to
the meter and isolator, I could cheaply enough add either a DIN rail
transformer or a single MCB feeding an adjacent fused connection unit
and thence the existing bell transformer.

We're getting there...


--
Kevin Poole
**Use current month and year to reply (e.g. )***
Car Transport by Tiltbed Trailer - based near Derby

On Tue, 28 Jun 2005 15:33:00 +0100,it is alleged that "Autolycus"
spake thusly in uk.d-i-y:

Can one reconfigure split-load CUs so that they have two RCDs, instead
of one plus an isolator? Without wishing to bring heavens or posters
with firm views crashing down on me, I've been running an entirely RCD
protected house (2 separate CUs) for well over 15 years with no nuisance
tripping, and lighting circuits split between the two to ensure nowhere
blacks out completely with just one fault. Otherwise it would need a
second Henley near two new small CUs.

Yep, just did that the other day, 100mA time delay RCD on the main,
protecting the lighting and the single 16A radial feeding the
fridge/freezer, and a normal 30mA feeding the second half of the CU
protecting everything else.

The setup is unusual in one other way, the 100mA protected side also
has a 30A/30mA RCBO in it (it was there already for a shower which is
now on the 30mA protected side) which feeds the outside sockets, to
prevent the likely nuisance tripping on the outside circuit from
killing everything. Expect however to pay much more/suffer less
availability for a time delay RCD, a 100mA RCD of the more usual sort
probably wouldn't prevent it tripping as well as the 30mA one in the
event of an earth fault in the range above 100mA.

--
There is not the slightest indication that nuclear energy will
ever be obtainable. It would mean that the atom would have to
be shattered at will.
- Albert Einstein, 1932

Autolycus wrote:

It's connected to the box, though without delving rather deeper in than
3-phase boxes encourage, I can't tell whether it's electrically as well
as mechanically connected - I assume so.

Given John's comments above it does sound more like PME then (the 16mm^2
earth wire is also a clue). Often these days the supply company sticks a
sticker on the setup to say so, but I guess you cannot rely on that.

No, I'm not convinced. I wonder if the supply company would have a record?

They ought to have... might be worth asking.

I think it a fair assumption that the connection on the side of the
service head is genuinely earthed, either via the cable sheath or the
Neutral: the upstairs flat has obviously been rewired relatively
recently, and has no other earth connection

Yup, I expect you are right.

Can one reconfigure split-load CUs so that they have two RCDs, instead
of one plus an isolator? Without wishing to bring heavens or posters

You can, and this is common practice on TT setups. However it looks
pretty unlikely that you are TT so there is no need for a 100mA RCD at all.

with firm views crashing down on me, I've been running an entirely RCD
protected house (2 separate CUs) for well over 15 years with no nuisance
tripping, and lighting circuits split between the two to ensure nowhere
blacks out completely with just one fault. Otherwise it would need a
second Henley near two new small CUs.

What many people call nuisance trips are in fact trips indicating a
fault of some description anyway. Although use of a "whole house" RCD is
deprecated, the main objection is the plunging into darkness aspect. It
is a problem you can solve in several ways - you have found one having
separately protected CUs.


--
Cheers,

John.

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