I participated in (but didn't initiate) the thread back in June - from which
I learned quite a lot - but have a few more questions.

My detached double garage is currently being built, and is about 1.1 metres
from the house. I intend to use a garage consumer unit - probably
http://tinyurl.com/zmmh4, which I intend to connect to a spare way in my
domestic CU. This
currently has a 6mm^2 T&E cable connected to it, which was originally
intended for an electric shower - but we used stored water and a shower pump
instead - so this way and cable (with a suitable MCB) can be re-deployed.

The 6mm^2 cable ends (with a couple of feet spare) just above the ceiling of
an en-suite bathroom - more or less vertically
above the point where the house end of the garage connection needs to be. I
intend to join some 6mm^2 SWA cable to this
cable, and take it through the wall and down the outside of the house, and
across a passage door frame into the garage.

Although the garage consumer unit can handle 40 amps, this is more than I
need (and the sum of the individual MCBs is a lot less than this anyway) so
I intend to use a 32 amp Type-B MCB at the house end of the connection -
which seems more
appropriate than a higher value if relying on the 2.5mm^2 earth within the
existing T&E cable.

My questions concern earthing arrangements, and physically joining the
cables together.

From my description of my incoming mains back in June, Andy Wade thought
that I have a TN-S system, and David Hansen thought it was more likely
TN-C-S. In case it helps, I've posted a photo of the main fuse and meter
connection at
http://www.mills37.plus.com/Incoming_mains.JPG Just to remind you, I
estimate that I have about 10 metres of T&E, and will need about 6 metres of
SWA.

The options for earthing appear to be as follows:

* Use 3-core SWA cable, and use one core (6 mm^2) as the earth - and join it
onto the end of the T&E's 2.5mm^2 protective earth conductor - thus
exporting the earth from the domestic CU

* Use 2-core SWA, and use the steel armour as an earth, again joined to the
T&E's earth conductor - again exporting the
earth. [There will be no external connections to be subjected to 'weather',
so corrosion shouldn't be a problem]

* Use 2-core SWA and an earth spike at the garage end - thus providing the
garage with its own earth - independent of the house supply

* Some combination of the above. [Is there a down side to exporting the
earth *and* having an earth spike?]

I would welcome constructive comments on the relative merits of each of the
above options - plus identification of any viable options I may have missed.

Now to joining the cables . .

The most convenient solution would be to have the joint inside a deep
(metal) socket box high on the wall of the en-suite
bathroom - sunk into the blockwork, and covered by a flush blanking plate.
The T&E would come down from above, and be chased into the plaster and the
SWA would go straight out through the wall from the back of the box - with
its gland fitted to a knock-out in the box. Does anyone see any problems
with this? How should I physically join the cables? Is a large chocolate
block connector (inside the box) ok - or is there anything purpose-made
which would be better? Do I need to earth the SWA's armour even if it isn't
being used as the protective earth?

Your expert advice will be much appreciated.

Oh, and in case anyone mentions Part P - I think that what I am doing is
probably covered by Part P. AIUI, extending an existing radial circuit
isn't, but when you start taking it outside, it is. The building itself is
exempt from building regs, being a detached garage of less than 30 M^2 floor
area, and meeting the other exemption conditions. My inclination therefore
is to forget about Part P and hope that it gets lost in the noise when the
property is eventually sold (hopefully far into the future). Nevertheless, I
want to ensure that I end up with a 'safe' electrical installation - hence
the questions.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored..
Messages sent to it may not be read for several weeks. PLEASE REPLY TO
NEWSGROUP!

Roger Mills wrote:

My detached double garage is currently being built, and is about 1.1 metres
from the house. I intend to use a garage consumer unit - probably
http://tinyurl.com/zmmh4, which I intend to connect to a spare way in my
domestic CU. This

It looks rather like the RCD covers both ways on that. Depending on how
you plan to use the garage you may wish to opt for some arrangement that
will not lose the lights at the same time you lop through a power cord
with a still spinning circular saw! (i.e. switched two way CU with a
RCBO for the sockets, or perhaps the one pictured with a non maintained
emergency light)

Although the garage consumer unit can handle 40 amps, this is more than I
need (and the sum of the individual MCBs is a lot less than this anyway) so
I intend to use a 32 amp Type-B MCB at the house end of the connection -
which seems more
appropriate than a higher value if relying on the 2.5mm^2 earth within the
existing T&E cable.

On the same theme as above you may need to bear in mind is
descrimination of the protective devices. You want to try and ensure
that a trip on the power circuit in the garrage only takes out the local
MCB and not the upstream one in the main CU as well hence losing your
lights.

My questions concern earthing arrangements, and physically joining the
cables together.

From my description of my incoming mains back in June, Andy Wade thought
that I have a TN-S system, and David Hansen thought it was more likely
TN-C-S. In case it helps, I've posted a photo of the main fuse and meter
connection at
http://www.mills37.plus.com/Incoming_mains.JPG Just to remind you, I
estimate that I have about 10 metres of T&E, and will need about 6 metres of
SWA.

That is a different cable head end from any I have seen in use in this
area, so can't give you a definitive answer. However the connection of
the (undersized!) earth connector to the side of the main cutout like
that would suggest TN-C-S.

Where does that other earth wire go that drops down from the CU? What is
that little box at the bottom of the frame?

The options for earthing appear to be as follows:

* Use 3-core SWA cable, and use one core (6 mm^2) as the earth - and join it
onto the end of the T&E's 2.5mm^2 protective earth conductor - thus
exporting the earth from the domestic CU

This is slightly more reliable that the next option in that there is
less chance of the earth becoming poor due to corrosian etc at the gland
- but as you later say these are internal connections and a new garage
is unlikly to be damp so there is not much in it. If doing this I would
tend to use one core *and* the screen.

* Use 2-core SWA, and use the steel armour as an earth, again joined to the
T&E's earth conductor - again exporting the
earth. [There will be no external connections to be subjected to 'weather',
so corrosion shouldn't be a problem]

One slight advantage with this one is the cable will be a little thinner
and easier to handle.

* Use 2-core SWA and an earth spike at the garage end - thus providing the
garage with its own earth - independent of the house supply

If the house end is not already TT then the arguments for a separate TT
supply in an outbuilding usually come down two one of two reasons -
either it is a long distance (obviuosly not the case here), or, when
there will be potential difficulty extending the house's equipotetial
zone into the outbuilding (of most concern with a PME house).

* Some combination of the above. [Is there a down side to exporting the
earth *and* having an earth spike?]

I would welcome constructive comments on the relative merits of each of the
above options - plus identification of any viable options I may have missed.

Now to joining the cables . .

The most convenient solution would be to have the joint inside a deep
(metal) socket box high on the wall of the en-suite
bathroom - sunk into the blockwork, and covered by a flush blanking plate.
The T&E would come down from above, and be chased into the plaster and the

If coming from above, could you not have an adaptable metal box in the
loft space instead?

SWA would go straight out through the wall from the back of the box - with
its gland fitted to a knock-out in the box. Does anyone see any problems
with this? How should I physically join the cables? Is a large chocolate
block connector (inside the box) ok - or is there anything purpose-made
which would be better?

You could use crimps, but since it will remain accessable screw
connectors are ok. If you opt for using the screen as a CPC I would be
reluctant to have the gland connection burried in a wall behind a metal
box.

Do I need to earth the SWA's armour even if it isn't
being used as the protective earth?

It is good practice since it offers better protection to the cable
(especially since you don't currently appear to have a RCD at the head
end). If you were using TT in the garage then you can earth it at the
head end, but leave the other end disconnected (would require a
insualted CU in the garage)

Your expert advice will be much appreciated.

As usual it is worth what you paid! ;-)

--
Cheers,

John.

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

On Thu, 24 Aug 2006 00:44:13 +0100 someone who may be John Rumm
wrote this:-

I've posted a photo of the main fuse and meter
connection at
http://www.mills37.plus.com/Incoming_mains.JPG

That is a different cable head end from any I have seen in use in this
area, so can't give you a definitive answer. However the connection of
the (undersized!) earth connector to the side of the main cutout like
that would suggest TN-C-S.

Agreed.

If you opt for using the screen as a CPC I would be
reluctant to have the gland connection burried in a wall behind a metal
box.

Agreed. An excellent way to introduce corrosion into the CPC. In
addition, although I don't share the panic about using steel as the
CPC I think it must be easily accessible for inspection. Provided
the extra lengths are acceptable I too would look at the loft as the
place to make the joint.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

John Rumm wrote:

It looks rather like the RCD covers both ways on that. Depending on how
you plan to use the garage you may wish to opt for some arrangement that
will not lose the lights at the same time you lop through a power cord
with a still spinning circular saw! (i.e. switched two way CU with a
RCBO for the sockets, or perhaps the one pictured with a non maintained
emergency light)

Yes, for TT a main switch and two RCBOs would be a good option, or main
switch with one MCB (lights) and one RCBO (power) for TN. I'd be
inclined to make the 'power' RCBO a 20 A one - RCBOs only come as Type B
and 16 A Type B might tend to trip on motor starting currents, or the
inrush current of a 230 - 115 V tool transformer. (Alternatively keep
the 16 A circuit for sockets only and provide separate motor circuits
for any machines.) You can buy all the MK consumer unit parts
separately from a wholesaler, including TLC if you want to buy on-line.

On the same theme as above you may need to bear in mind is
descrimination of the protective devices. You want to try and ensure
that a trip on the power circuit in the garrage only takes out the local
MCB and not the upstream one in the main CU as well hence losing your
lights.

That would probably require the feed to be via a separate switch-fuse
rather than an MCB in the CU - certainly a better arrangement, but does
involve teeing in to the meter tails with a service connector block.

That is a different cable head end from any I have seen in use in this
area, so can't give you a definitive answer. However the connection of
the (undersized!) earth connector to the side of the main cutout like
that would suggest TN-C-S.

Looks like TN-C-S to me, with old earthing and bonding conductors which
are undersized by current standards. These ought to be upgraded if you
intend to use the exported PME earth.

Where does that other earth wire go that drops down from the CU?

One of the main bonds?

What is that little box at the bottom of the frame?

Looks a bit like an old GPO telephone wiring junction box (a 'block
terminal' something-or-other)?

* Use 3-core SWA cable, and use one core (6 mm^2) as the earth - and
join it onto the end of the T&E's 2.5mm^2 protective earth conductor -
thus exporting the earth from the domestic CU

This is slightly more reliable that the next option in that there is
less chance of the earth becoming poor due to corrosian etc at the gland
- but as you later say these are internal connections and a new garage
is unlikly to be damp so there is not much in it. If doing this I would
tend to use one core *and* the screen.

* Use 2-core SWA, and use the steel armour as an earth, again joined
to the T&E's earth conductor - again exporting the
earth. [There will be no external connections to be subjected to
'weather', so corrosion shouldn't be a problem]

One slight advantage with this one is the cable will be a little thinner
and easier to handle.

Using a core as CPC gives you a 6 mm^2 conductor with a resistance of
about 3.7 milliohm/m. Using the armour gives you a CPC equivalent to
9.8 mm^2 copper, but with a resistance of around 7 milliohm/m. I'd use
the 2-core unless the CPC resistance (R2) is a problem in the design.

The weakest link in this design though is the 2.5 mm^2 CPC in the T&E
cable. Note that it would not be acceptable to use this if there are
any metal services rising in the garage that would need main bonding -
this because the CPC of the submain also acts as the main bonding
conductor, so would need to be a minimum of 10 mm^2 Cu equivalent.

* Use 2-core SWA and an earth spike at the garage end - thus providing
the garage with its own earth - independent of the house supply

If the house end is not already TT then the arguments for a separate TT
supply in an outbuilding usually come down two one of two reasons -
either it is a long distance (obviuosly not the case here), or, when
there will be potential difficulty extending the house's equipotetial
zone into the outbuilding (of most concern with a PME house).

As I usually say here, the TT/TN decision depends on the use of the
outbuilding and the practicality of creating an equipotential zone
there. At one extreme is a dry workshop building where there will be
little use of electrical equipment outdoors (TN OK here) and at the
other extreme is the metal greenhouse (TT essential). Any use extensive
of portable Class 1 (earthed) equipment outdoors again signals the need
for TT earthing.

* Some combination of the above. [Is there a down side to exporting
the earth *and* having an earth spike?]

No, and there is an advantage to doing that - but understand that it's
still TN-C-S with its attendant risks. You are adding another earth to
the M (multiple) in PME, so you'll help reduce the touch voltage in the
event of a broken supply neutral. You do need a damn good earth
electrode to do much good though, and it should be connected to the main
earth terminal in the house, not at the garage end via a weedy 2.5 mm^2 CPC.

[...]
SWA would go straight out through the wall from the back of the box -
with its gland fitted to a knock-out in the box. Does anyone see any
problems with this?

That's completely impractical because you've go no access to the back of
the box to tighten the gland nut. It would also be extremely fiddly to
do this with a single-gang accessory box. Better as John said to
connect the SWA in the loft, alternatively take the T&E through the wall
to a box on the outside, and run the SWA straight down from there.

[...]
Do I need to earth the SWA's armour even if it isn't being used as
the protective earth?

Yes, definitely, to provide protection in case the cable is damaged.

--
Andy

Andy Wade wrote:
John Rumm wrote:

On the same theme as above you may need to bear in mind is
descrimination of the protective devices. You want to try and ensure
that a trip on the power circuit in the garrage only takes out the
local MCB and not the upstream one in the main CU as well hence losing
your lights.


That would probably require the feed to be via a separate switch-fuse
rather than an MCB in the CU - certainly a better arrangement, but does
involve teeing in to the meter tails with a service connector block.

Hager do a MCB sized HRC fuse carrier, which can solve that problem in
many cases.... although having just typed that, I remembered that
Roger's CU ain't a DIN rail jobbie anyway, so this is of little
practical use to him! ;-)


--
Cheers,

John.

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

John Rumm wrote:

Hager do a MCB sized HRC fuse carrier, which can solve that problem in
many cases....

Oops, quite right, I forgot that option.

although having just typed that, I remembered that
Roger's CU ain't a DIN rail jobbie anyway, so this is of little
practical use to him! ;-)

Doh! - his picture tells all, and I guess the new circuit is going in
the empty fuseway on the right (currently 15 A). In this case the
obvious thing to do is to use a 30 A BS 1361 fuse and not another
plug-in MCB.

--
Andy

In an earlier contribution to this discussion,
Andy Wade wrote:

John Rumm wrote:

Hager do a MCB sized HRC fuse carrier, which can solve that problem
in many cases....

Oops, quite right, I forgot that option.

although having just typed that, I remembered that
Roger's CU ain't a DIN rail jobbie anyway, so this is of little
practical use to him! ;-)

Doh! - his picture tells all, and I guess the new circuit is going in
the empty fuseway on the right (currently 15 A). In this case the
obvious thing to do is to use a 30 A BS 1361 fuse and not another
plug-in MCB.

Yes, the circuit is going at the extreme right - which currently has a blue
base for a 16A MCB.

I may well still have a 30A fuse - not sure about the BS1361 bit though - is
that something special? [The CU started off with fuses, and was converted to
MCBs!]

What is the rationale for using a fuse rather than an MCB? Is it that it
takes longer to blow, making it more likely that the one at the garage end
will trip instead? If so, it makes sense, but it flies in the face of the
advice given in the earlier thread which said that I needed a Type B (and
*not* Type C) MCB on account of only having a 2.5mm^2 earth wire for most of
the length.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

In an earlier contribution to this discussion,
John Rumm wrote:


On the same theme as above you may need to bear in mind is
descrimination of the protective devices. You want to try and ensure
that a trip on the power circuit in the garrage only takes out the
local MCB and not the upstream one in the main CU as well hence
losing your lights.

Many thanks for your response.

The local MCBs are 16A for power and 6A for lighting - so, under overload
conditions, should trip prior to the 32A one at the house end. Of course, if
I cut through a wire and connect live to earth before live to neutral, the
RCD will trip and I'll lose the lights as well. I guess I have to live with
that.



That is a different cable head end from any I have seen in use in this
area, so can't give you a definitive answer. However the connection of
the (undersized!) earth connector to the side of the main cutout like
that would suggest TN-C-S.

Where does that other earth wire go that drops down from the CU? What
is that little box at the bottom of the frame?

The other earth wire goes into an adjoining cupboard which houses the gas
meter, and is clamped onto a gas pipe. The little box at the bottom is a
junction box for telephone wiring.




If coming from above, could you not have an adaptable metal box in the
loft space instead?

I *could* join it in the loft space - but that bit of loft is pretty
inaccessible, so I was trying to avoid it. What does an adaptable metal box
look like?


You could use crimps, but since it will remain accessable screw
connectors are ok. If you opt for using the screen as a CPC I would be
reluctant to have the gland connection burried in a wall behind a
metal box.

I guess I'd need a half-way decent ratchet crimping tool to use crimps -
which I don't have. I take your point about burying the gland in the wall.


Your expert advice will be much appreciated.

As usual it is worth what you paid! ;-)

If you're selective about what advice you accept, much of the advice given
here is actually worth a lot more than we pay for it!
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

Roger Mills wrote:

Many thanks for your response.

The local MCBs are 16A for power and 6A for lighting - so, under overload
conditions, should trip prior to the 32A one at the house end. Of course, if
I cut through a wire and connect live to earth before live to neutral, the
RCD will trip and I'll lose the lights as well. I guess I have to live with
that.

By a slight change to the choice of CU though that is easy enough to avoid.

Where does that other earth wire go that drops down from the CU? What
is that little box at the bottom of the frame?


The other earth wire goes into an adjoining cupboard which houses the gas
meter, and is clamped onto a gas pipe.

So no main bond to the water service then?

The little box at the bottom is a
junction box for telephone wiring.

Thought as much, but thought I had better check!

If coming from above, could you not have an adaptable metal box in the
loft space instead?


I *could* join it in the loft space - but that bit of loft is pretty
inaccessible, so I was trying to avoid it. What does an adaptable metal box
look like?

Box looks like:

http://www.tlc-direct.co.uk/Main_Ind...ble/index.html
or
http://www.tlc-direct.co.uk/Main_Ind...ded/index.html

You could use crimps, but since it will remain accessable screw
connectors are ok. If you opt for using the screen as a CPC I would be
reluctant to have the gland connection burried in a wall behind a
metal box.


I guess I'd need a half-way decent ratchet crimping tool to use crimps -
which I don't have. I take your point about burying the gland in the wall.

In which case why not chase down the bathroom wall as described, but
rather than installing a metal box in the bathroom, simply drill
throught the wall at that point (keeping within 6" of the bathroom
ceiling). You can stick some capping over the T&E to facilitate future
replacement if you wish.

Now install your cable and plaster over the chase leaving no visible
accessory in the bathroom. Now visit the other side of the wall where
hopefully you have a bit of T&E dangling, and poke it into the back of
one of the aformentiond boxes (a IP65 one would probably be a good
choice here). Screw it to the wall, and you can then stick a nice neat
SWA gland into the knockout at the base of the box. Choose the right box
ad you may even get one complete with junction terminals. That means
your joint is accessable and serviceable, no extra clutter to tile round
the bathroom, and no groveling in the loft!

Your expert advice will be much appreciated.

As usual it is worth what you paid! ;-)


If you're selective about what advice you accept, much of the advice given
here is actually worth a lot more than we pay for it!

Yup, second that many times over, thanks guys!

--
Cheers,

John.

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

In an earlier contribution to this discussion,
John Rumm wrote:


The local MCBs are 16A for power and 6A for lighting - so, under
overload conditions, should trip prior to the 32A one at the house
end. Of course, if I cut through a wire and connect live to earth
before live to neutral, the RCD will trip and I'll lose the lights
as well. I guess I have to live with that.

By a slight change to the choice of CU though that is easy enough to
avoid.
Could you elaborate on that please?


The other earth wire goes into an adjoining cupboard which houses
the gas meter, and is clamped onto a gas pipe.

So no main bond to the water service then?

Yes there *is* - but the water comes in elsewhere. The earth wire goes up
through the ceiling from the CU, and drops down into the kitchen where the
mains stop-tap is located.


Box looks like:

http://www.tlc-direct.co.uk/Main_Ind...ble/index.html
or
http://www.tlc-direct.co.uk/Main_Ind...ded/index.html

Thanks for the links. I now see what you mean.


I take your point about burying the gland in the wall.

In which case why not chase down the bathroom wall as described, but
rather than installing a metal box in the bathroom, simply drill
throught the wall at that point (keeping within 6" of the bathroom
ceiling). You can stick some capping over the T&E to facilitate future
replacement if you wish.

Now install your cable and plaster over the chase leaving no visible
accessory in the bathroom. Now visit the other side of the wall where
hopefully you have a bit of T&E dangling, and poke it into the back of
one of the aformentiond boxes (a IP65 one would probably be a good
choice here). Screw it to the wall, and you can then stick a nice neat
SWA gland into the knockout at the base of the box. Choose the right
box ad you may even get one complete with junction terminals. That
means your joint is accessable and serviceable, no extra clutter to tile
round the bathroom, and no groveling in the loft!


That's certainly a possibility. It means that I would be making the
connection while perched 16' up a ladder, but I could probably terminate the
SWA in the box before fixing the box to the wall. How would I seal round
where the T&E would come in?
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

Although the garage consumer unit can handle 40 amps, this is more than I
need (and the sum of the individual MCBs is a lot less than this anyway)
so I intend to use a 32 amp Type-B MCB at the house end of the
connection - which seems more appropriate than a higher value if relying
on the 2.5mm^2
earth within the existing T&E cable.

Don't be so sure. You want the house end to blow as slowly as possible to
get maximum possible discrimination with the garage CU. I would consider a
Type C MCB, or even an HRC fuse. If 40A is allowed as well, then use that,
too. I haven't done the calculations so can't tell you what you will get
away with. This way, any fault is more likely to be picked up at the local
MCB in the garage.

* Use 3-core SWA cable, and use one core (6 mm^2) as the earth - and join
it onto the end of the T&E's 2.5mm^2 protective earth conductor - thus
exporting the earth from the domestic CU

I'd just do this given you are only 1.1m from the house. This is only
possible if the garage has no main equipotential bonding requirements, or
the main equipotential bonding can actually be achieved.

Remember to use the armour as earth as well, both to get the ELI even lower
and because the armour must be earthed anyway. The reason to have the
additional copper conductor is that copper doesn't rust at the termination
and is more reliable over the decades.

The most convenient solution would be to have the joint inside a deep
(metal) socket box high on the wall of the en-suite
bathroom - sunk into the blockwork, and covered by a flush blanking plate.
The T&E would come down from above, and be chased into the plaster and the
SWA would go straight out through the wall from the back of the box - with
its gland fitted to a knock-out in the box. Does anyone see any problems
with this?

No problem.

How should I physically join the cables? Is a large chocolate block
connector (inside the box) ok - or is there anything purpose-made which
would be better?

Chocolate block or crimp is fine.

Do I need to earth the SWA's armour even if it isn't being used as the
protective earth?

Yes. Either earthed by using a metal box, or using a decent earth ring, not
the ****e one that you get with the gland.

Christian.

In an earlier contribution to this discussion,
Christian McArdle wrote:


Don't be so sure. You want the house end to blow as slowly as
possible to get maximum possible discrimination with the garage CU. I
would consider a Type C MCB, or even an HRC fuse. If 40A is allowed
as well, then use that, too. I haven't done the calculations so can't
tell you what you will get away with. This way, any fault is more
likely to be picked up at the local MCB in the garage.


Is there an idiot's guide somewhere, defining the calculations which I need
to do?

As mentioned in my post in answer to Andy Wade, I had previously been
advised (back in June) to use a Type B MCB, and to go for 32A rather than
40A in the light of my rather weedy 2.5mm^2 earth wire - so I'm getting a
bit confused!

* Use 3-core SWA cable, and use one core (6 mm^2) as the earth - and
join it onto the end of the T&E's 2.5mm^2 protective earth conductor
- thus exporting the earth from the domestic CU

I'd just do this given you are only 1.1m from the house. This is only
possible if the garage has no main equipotential bonding
requirements, or the main equipotential bonding can actually be
achieved.
It's 1.1 metres as the crow flies - but about 6 metres of SWA down the wall,
across the gap, and into the garage. Does this make any difference - or are
we only looking at the likely difference in earth potential between 2
adjacent buildings?
There will be no 'services' (water, gas, etc) in the garage, and no
equipotential bonding is required AIUI.

--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

Roger Mills wrote:
ice will be much appreciated.

Oh, and in case anyone mentions Part P - I think that what I am doing is
probably covered by Part P. AIUI, extending an existing radial circuit
isn't, but when you start taking it outside, it is. The building itself is
exempt from building regs, being a detached garage of less than 30 M^2 floor
area, and meeting the other exemption conditions. My inclination therefore
is to forget about Part P and hope that it gets lost in the noise when the
property is eventually sold (hopefully far into the future). Nevertheless, I
want to ensure that I end up with a 'safe' electrical installation - hence
the questions.


a) It's covered by part P
b) I'd google anyone I was buying a house from, and find this thread.
c) It probably won't get lost in the noise, because it's the noise that
is precisely the problem when buying a house. Well, that and solicitors
covering their backs.
d) But, if I found it by google, I'd then chat to you, and provided I
was convinced that you knew what you were doing and did it properly, I'd
tell you to forget about disclosing anything about it, and the
solicitors would never be the wiser. Much the best way.

Anyway, just pointing out that posting plans to ignore buildings control
isn't a good idea when done under your real name!


Cheers,

Ben

Ben Blaukopf wrote:

Roger Mills wrote:

Oh, and in case anyone mentions Part P - I think that what I am doing
is probably covered by Part P. AIUI, extending an existing radial
circuit isn't, but when you start taking it outside, it is. The
building itself is exempt from building regs, being a detached garage
of less than 30 M^2 floor area, and meeting the other exemption
conditions. My inclination therefore is to forget about Part P and
hope that it gets lost in the noise when the property is eventually
sold (hopefully far into the future). Nevertheless, I want to ensure
that I end up with a 'safe' electrical installation - hence the
questions.



a) It's covered by part P

Yup, agreed.

b) I'd google anyone I was buying a house from, and find this thread.

I bet few would though.... still its certainly possible.

(I hope you like reading - there are getting on for 10,000 posts that
mention Rogers's name!)

c) It probably won't get lost in the noise, because it's the noise that
is precisely the problem when buying a house. Well, that and solicitors
covering their backs.

I expect a few years into the future they wil be showing as much
interest as they do in FENSA certs now (i.e. getting progressively less)

d) But, if I found it by google, I'd then chat to you, and provided I
was convinced that you knew what you were doing and did it properly, I'd
tell you to forget about disclosing anything about it, and the
solicitors would never be the wiser. Much the best way.

Yup, I would much rather find evidence of someone asking sensible
questions before doing a job!

Anyway, just pointing out that posting plans to ignore buildings control
isn't a good idea when done under your real name!

Hmmm, doubt there are many on this group who haven't wrt part P!

--
Cheers,

John.

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