Adding a new out-building to my house and just pondering the
electricity supply to it. (ignoring issue of whether I am allowed to
do this)

Only need a couple of lights and a couple of sockets (ad hoc use only)
Intend fitting a Garage CU ,,, 40A 30mA RCD – 1 x 16A for sockets 1 x
6A for lights

Current house install is Supply authority cabinet .. cabled with 32mm
tails to a 100A switch fuse which in turn goes to a Henley block and
feeds
2 x CU's. (wanted plenty of circuit granularity)
Be interested in knowing which option to follow…

Opt A … put a DP switch alongside the switch fuse (downstream of the
fuse) and feed that via armoured cable to the outbuilding, and
install the garage CU … i.e. the DP sw allows complete isolation of
outbuilding without impacting house.

Opt B .. add a 40A mcb into one of the existing house CU's, and then
run feed to
outbuilding and it's CU.
Does not allow full `isolation' but mcb would allow power interruption
of that feed.

Be interested in views … and whether Regs call for Opt A .. i.e.
local isolation.

Osprey wrote:
Adding a new out-building to my house and just pondering the
electricity supply to it. (ignoring issue of whether I am allowed to
do this)

Only need a couple of lights and a couple of sockets (ad hoc use only)
Intend fitting a Garage CU ,,, 40A 30mA RCD – 1 x 16A for sockets 1 x
6A for lights

I would use a 20A MCB for the sockets, as per a normal radial circuit,
assuming you are wiring it in 2.5mm cable.

Current house install is Supply authority cabinet .. cabled with 32mm
tails to a 100A switch fuse which in turn goes to a Henley block and
feeds
2 x CU's. (wanted plenty of circuit granularity)
Be interested in knowing which option to follow…

Opt A … put a DP switch alongside the switch fuse (downstream of the
fuse) and feed that via armoured cable to the outbuilding, and
install the garage CU … i.e. the DP sw allows complete isolation of
outbuilding without impacting house.

If this new switch is just going to be a switch, then your run to the
out-building is going to need a HUGE cable as it will be fused at 100A
You would need to install a switch fuse with an appropriate fuse if you want
to use a sensible sized cable.

Opt B .. add a 40A mcb into one of the existing house CU's, and then
run feed to
outbuilding and it's CU.
Does not allow full `isolation' but mcb would allow power interruption
of that feed.

This is what I have done, but I used a 32A MCB, and made sure it was
connected to the non RCD consumer unit.

Be interested in views … and whether Regs call for Opt A .. i.e.
local isolation.

The main switch in the CU will act as local isolation, and as you will put
it on a non RCD side, you wont have any problems with RCD's tripping because
there is a neutral problem.

More information is needed really..

How long is the cable run between the house CU and the outbuilding CU
What cable are you planning on using (Have you installed this already?)
What is the out-building made of?
Are there any other services to this out-building (Water/Gas/etc.)

Toby...

Osprey wrote:

Current house install is Supply authority cabinet .. cabled with 32mm
tails to a 100A switch fuse which in turn goes to a Henley block and
feeds
2 x CU's. (wanted plenty of circuit granularity)
Be interested in knowing which option to follow…

Opt A … put a DP switch alongside the switch fuse (downstream of the
fuse) and feed that via armoured cable to the outbuilding, and
install the garage CU … i.e. the DP sw allows complete isolation of
outbuilding without impacting house.

You would need a fuse/mcb at the head end to protect the submain from
overcurrent or fault currents, unless it is of sufficient size that the
main 100A cutout can perform this task (which seems a bit excessive for
a few sockets and a light)

Opt B .. add a 40A mcb into one of the existing house CU's, and then
run feed to
outbuilding and it's CU.
Does not allow full `isolation' but mcb would allow power interruption
of that feed.

Full isolation would come via turning off the CU its fed from, not its MCB

How about:

Opt 3 - install third mini CU at the head end, fed via additional set of
tails from the Henley. This could have a single fuse or MCB of
appropriate size, and a master switch. Hence protecting the submain, and
providing ready isolation discrete from any other circuits.


More detail he

http://wiki.diyfaq.org.uk/index.php?...ricity_outside


--
Cheers,

John.

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More detail he

http://wiki.diyfaq.org.uk/index.php?...ricity_outside



My description may not have been that clear … though both comments are
useful.

Current house install is Supply authority cabinet .. cabled with 32mm tails
to a 100A switch fuse which in turn goes to a Henley block and feeds 2 x
CU's. (wanted plenty of circuit granularity)

I want to supply a feed to an outbuilding (new garage) … intend putting a
small Cu in garage consisting of 40A 30mA RCD plus 16A & 6A mcb for
limited light & power.
Something like .. http://tinyurl.com/6rozky
No other services - & this is a permanent building. Dug a trench last
night, The run to this from house is 10m long and will be in 3core armoured,
not checked but assuming it will be 2.5mm2

It would seem to make sense to have this capable of isolation from house …
Opt A … put a 40A DP switch fuse alongside the existing switch fuse
(downstream of the
fuse) and feed that via armoured cable to the outbuilding, and install the
garage CU … i.e. the DP sw allows complete isolation of outbuilding without
impacting house. 40A fuse limits fault current to sub cct.

Opt B .. add a 40A mcb into one of the existing house CU's, and then run
feed from this to outbuilding and it's CU.
Does not allow full `isolation' without affecting house CU.
If I do use Opt B … then guess I would have to terminate SWA cable in box of
some sort alongside CU to allow a gland and correct earthing & termination
of armour wires etc.

I have sketched out the existing installation and 2 options …
http://tinyurl.com/5ddcun

"Rick Hughes" wrote in message
...


More detail he

http://wiki.diyfaq.org.uk/index.php?...ricity_outside



My description may not have been that clear … though both comments are
useful.

Current house install is Supply authority cabinet .. cabled with 32mm
tails to a 100A switch fuse which in turn goes to a Henley block and
feeds 2 x CU's. (wanted plenty of circuit granularity)

I want to supply a feed to an outbuilding (new garage) … intend putting a
small Cu in garage consisting of 40A 30mA RCD plus 16A & 6A mcb for
limited light & power.
Something like .. http://tinyurl.com/6rozky
No other services - & this is a permanent building. Dug a trench last
night, The run to this from house is 10m long and will be in 3core
armoured, not checked but assuming it will be 2.5mm2

It would seem to make sense to have this capable of isolation from house …
Opt A … put a 40A DP switch fuse alongside the existing switch fuse
(downstream of the
fuse) and feed that via armoured cable to the outbuilding, and install the
garage CU … i.e. the DP sw allows complete isolation of outbuilding
without impacting house. 40A fuse limits fault current to sub cct.

Opt B .. add a 40A mcb into one of the existing house CU's, and then run
feed from this to outbuilding and it's CU.
Does not allow full `isolation' without affecting house CU.
If I do use Opt B … then guess I would have to terminate SWA cable in box
of some sort alongside CU to allow a gland and correct earthing &
termination of armour wires etc.

I have sketched out the existing installation and 2 options …
http://tinyurl.com/5ddcun


If you use option B then terminate the armoured into a metal clad 45Amp
switch. (eg
http://www.sparksdirect.co.uk/metal-clad-1-gang-45-amp-dp-red-rocker-switch-with-neon-p-13999.html
) Not only will this allow a good strong point for the armoured to
terminate you will then have your double pole isolation in the house.

There is little to chose beween options A and B. With option A you will
still have to find a 40A DP switched fuse or a 2 way CU that will take your
armoured.

Personally I would also look up the difference in cost between 2.5mm and 4mm
armoured. I suspect 10m of 2.5 armoured plus the wiring in the outbuilding
will be big enough the expected voltage drop.

Adam

"ARWadworth" wrote in message
m...


If you use option B then terminate the armoured into a metal clad 45Amp
switch. (eg
http://www.sparksdirect.co.uk/metal-clad-1-gang-45-amp-dp-red-rocker-switch-with-neon-p-13999.html
) Not only will this allow a good strong point for the armoured to
terminate you will then have your double pole isolation in the house.


That is simpler (and presumably cheaper) than a switch fuse :-) not
thought of that.



There is little to chose beween options A and B. With option A you will
still have to find a 40A DP switched fuse or a 2 way CU that will take
your armoured.

Personally I would also look up the difference in cost between 2.5mm and
4mm armoured. I suspect 10m of 2.5 armoured plus the wiring in the
outbuilding will be big enough the expected voltage drop.



Yep - not done the math's yet, but 4mm2 will be about 30% higher in cost ..
plus not as easy to route, but I'll have to check the voltage drop.

Rick Hughes wrote:

It would seem to make sense to have this capable of isolation from house …
Opt A … put a 40A DP switch fuse alongside the existing switch fuse
(downstream of the
fuse) and feed that via armoured cable to the outbuilding, and install
the garage CU … i.e. the DP sw allows complete isolation of outbuilding
without impacting house. 40A fuse limits fault current to sub cct.

Yup, that is fine, so long as you have the spare terminal capacity on
the output of the existing switch fuse to get the new cable in. (this is
essentially what I was suggesting as my option 3 - although taking the
feed from the existing Henly. Obviously go with whichever is easiest and
in the best location.

Opt B .. add a 40A mcb into one of the existing house CU's, and then run
feed from this to outbuilding and it's CU.
Does not allow full `isolation' without affecting house CU.
If I do use Opt B … then guess I would have to terminate SWA cable in
box of some sort alongside CU to allow a gland and correct earthing &
termination of armour wires etc.

Yup, as Adam said, stick a small metal clad enclosure in somewhere with
a DP switch and you have another workable solution.

I have sketched out the existing installation and 2 options …
http://tinyurl.com/5ddcun

I would be tempted to up the size of the SWA a bit (using two core with
armour for earth would keep the overall size about the same).

If you max design load in the garage is 26A then your voltage drop on
2.5mm^2 SWA is well in spec, but it limits your future options a bit.

--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

I would be tempted to up the size of the SWA a bit (using two core with
armour for earth would keep the overall size about the same).

If you max design load in the garage is 26A then your voltage drop on
2.5mm^2 SWA is well in spec, but it limits your future options a bit.

--
Cheers,

John.

John ...

What is the 'current considered view on using SWA as earth ? ....

When I last asked on this site why someone was running in a separate
earth, was told that it is not acceptable good wiring practise to rely
on SWA for earth fault protection on consumer side of installation ?

The c/s area of armour is less than any one of the cores, and thus it
is not suitable to be used as a bonding conductor.
It therefore cannot be used as as a sub-main, but it can be used as a
final sub-circuit.
I am not sure what my use would be classed as. ?


I have 2 garages as part of the house ... and have multiple outlets
there including 32A industrial ones .. the new outbuildings do not
need much in way of power ...

Estimating total cable run (excluding wiring in outbuilding) as 15m
and max current load as 22A (16 + 6), then using 18mV/A/M would give
me 5.94V on 2.5mm2 (well under permitted 9.2V)
and 3.63V on 4mm2 ...

That makes 2.5mm2 more than man enough for the job ...

However I would consider going to 4mm2 if dropping off the earth is
allowable for this installation. (as per above comment) ... any
comments ?

Osprey wrote:

What is the 'current considered view on using SWA as earth ? ...

Same as it's always been, it's allowable, desirable and from the point
of view of saving valuable copper it's best practice. For cables of
sizes likely to be used for DIY it will rarely if ever be necessary to
use a separate circuit protective conductor (CPC). Even if a separate
CPC is used it's still necessary to earth the armour.

When I last asked on this site why someone was running in a separate
earth, was told that it is not acceptable good wiring practise to rely
on SWA for earth fault protection on consumer side of installation ?

This is quite untrue. Good practice does of course mean using the
correct size and type of glands.

The c/s area of armour is less than any one of the cores,

That's not true for any 2-core SWA size up to and including 120 mm^2
(XLPE cables to BS 5467). For the small sizes the armour CSA is much
larger than the cores - e.g. 6 mm^2 2-core has 22 mm^2 of steel armour.

Moreover the _copper_equivalent_ size of the armour (obtained by
dividing the steel area by 2.255) complies with the tabulated
requirements for use as a CPC without further calculation for all SWA
sizes up to and including 95 mm^2. [Ref. Table 54G in BS 7671 (Table
54.7 in the 17th ed.)]

The only thing that you have to watch is that the resistance per metre
of the armour may be higher than for the line and neutral conductors,
and you need to take this into account when evaluating the earth fault
loop impedance (Zs).

and thus it is not suitable to be used as a bonding conductor.

If the armour has to act as a main bonding conductor as well as a CPC
(e.g. for a submain to an outbuilding with services that need main
bonding) then you'll usually need 10 mm^2 copper equivalent (for PME
supplies). This, by coincidence, means using at least 10 mm^2 2-core SWA.

Estimating total cable run (excluding wiring in outbuilding) as 15m
and max current load as 22A (16 + 6), then using 18mV/A/M would give
me 5.94V on 2.5mm2 (well under permitted 9.2V)

As an aside, the voltage drop limits (guidance) have changed in the 17th
ed. and are now 3% for lighting and 5% for all other uses. Also you
must allow for drop in the outbuilding's wiring in addition to the submain.

That makes 2.5mm2 more than man enough for the job ...

Check the Zs though. The armour resistance of 2.5 SWA is 8.8 milliohm/m
at 20 deg. so applying the usual rule of thumb for heating under fault
conditions it will contribute about 0.18 ohm to Zs. What's the
protection on the supply side? - if you have a 30 A fuse and a TN-S
supply you might be getting near the limit...

However I would consider going to 4mm2 if dropping off the earth is
allowable for this installation. (as per above comment) ... any
comments ?

I'd go for at least 4, and possibly 6 for this. Incremental cost is
small and extra capacity always useful in the future. And as I said, if
you're exporting a PME earth and anything needs main bonding at the far
end you must use 10, or run a separate bonding conductor.

See also John Peckham's article here
http://www.gadsolutions.biz/electric...wa-as-cpc.html

--
Andy

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


The c/s area of armour is less than any one of the cores,

That's not true for any 2-core SWA size up to and including 120 mm^2 (XLPE
cables to BS 5467). For the small sizes the armour CSA is much larger
than the cores - e.g. 6 mm^2 2-core has 22 mm^2 of steel armour.


If the armour has to act as a main bonding conductor as well as a CPC
(e.g. for a submain to an outbuilding with services that need main
bonding) then you'll usually need 10 mm^2 copper equivalent (for PME
supplies). This, by coincidence, means using at least 10 mm^2 2-core SWA.

Estimating total cable run (excluding wiring in outbuilding) as 15m
and max current load as 22A (16 + 6), then using 18mV/A/M would give

See also John Peckham's article here
http://www.gadsolutions.biz/electric...wa-as-cpc.html

Andy as usual - many thanks

I looked back at original comments here regarding not using earth wires ..
and it was threaded to bonding conductor requirements.
So 4mm2 it is, off to TLC this morning then.

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

What is the 'current considered view on using SWA as earth ? ...

I'd go for at least 4, and possibly 6 for this. Incremental cost is
small and extra capacity always useful in the future. And as I said, if
you're exporting a PME earth and anything needs main bonding at the far
end you must use 10, or run a separate bonding conductor.

See also John Peckham's article here
http://www.gadsolutions.biz/electric...wa-as-cpc.html


On further Q ... if you could help

Existing house installation is on a PME (TN-C-S), but still classed as
temporary supply (in final permanent location) and therefore using my own
supplied earth rod. (been on this supply for 8 years )

Should I be exporting this earth to the outbuildings .. or should I insulate
armour wires at outbuilding end and install a local earth rod ?
At some point in future house will have it's acceptance certificate and I
will request Supply Authority change supply over to a permanent one, at
which point they will switch me to their earth.

If I do use a local earth rod at out buildings do I then disconnect this
when I go on permanent supply, or is it just left in place as another
'multiple earth point'


There are no other services in the outbuildings.

Rick Hughes wrote:

Existing house installation is on a PME (TN-C-S), but still classed as
temporary supply (in final permanent location) and therefore using my
own supplied earth rod. (been on this supply for 8 years )

With everything on one 30 mA RCD too, I guess...

Should I be exporting this earth to the outbuildings .. or should I
insulate armour wires at outbuilding end and install a local earth rod ?
At some point in future house will have it's acceptance certificate and
I will request Supply Authority change supply over to a permanent one,
at which point they will switch me to their earth.

In which case you should design the outbuilding installation on the
assumption that the house will eventually be PME.

The first decision is will the outbuilding use the exported house earth
or be a separate TT installation. The basic question is "are you likely
to come into simultaneous contact with the exported 'earth' (which will
rise in potential during a fault) and the local ground, or metal things
in contact with the local ground". Don't export PME if you're likely to
use Class 1 (earthed) equipment outdoors, or to a workshop with a bare
concrete floor, or to a metal greenhouse, and certainly not to a caravan
or boat (the last two being illegal under the ESQC regs). TT is the
safer option, provided your earth electrode remains in good condition
(and remains connected!) and provided you test the RCDs regularly.

For (eventual) exported PME option connect the armour solidly at both
ends. Under the temporary arrangements this will give you TT
throughout. There's no need for a separate earth rod at the outbuilding
end, although you can add one if you like belt and braces. Assuming the
plan is eventually to feed the submain via a fuse or MCB as a
non-RCD-protected distribution circuit, you'll need one or more RCDs in
the outbuilding (probably just a single 30 mA RCD if it's only a a few
lights and sockets as described). Under the temporary arrangement
you'll have two RCDs in cascade - so no discrimination - but this will
eventually resolve itself.

If the outbuilding is to be separately TT-earthed then, as you say,
earth the armour at the house end only. Isolate and insulate it at the
far end using an insulating gland (expensive) or use a big plastic
stuffing gland and heatshrink sleeving. Earth the installation to a
decent earth rod, preferably two 4ft. sections to get down to a good
depth below any likely frost. The earthing conductor (rod to disboard),
if normal 6491X green/yellow wire without mechanical protection, should
be 16 mm^2 to comply with regs. RCD(s) as above are required and the
discrimination issue remains until the house is converted to PME.

[Exported PME)
If I do use a local earth rod at out buildings do I then disconnect this
when I go on permanent supply, or is it just left in place as another
'multiple earth point'

Since you're using a fairly small cable I'd disconnect it. If the cable
were big enough to satisfy the 10 mm^2 copper equivalent requirement for
a main bonding conductor it would be safe to leave it in place.

--
Andy

"Andy Wade" wrote in message
...
Rick Hughes wrote:

Existing house installation is on a PME (TN-C-S), but still classed as
temporary supply (in final permanent location) and therefore using my own
supplied earth rod. (been on this supply for 8 years )

With everything on one 30 mA RCD too, I guess...


Andy ,,
Seems to be raising more questions than I thought.
Some answers to questions raised.

With everything on one 30 mA RCD too, I guess..

No, the existing house install has 2 CU's ...
One of which is 30mA RCD protected ... ring mains & radials
The other a Split load .. providing some non-protected (freezer, alarm, smk
detectors etc.) and the rest via a 100mA RCD for lighting circuits.

Don't export PME ... to a workshop with a bare concrete floor

Outbuilding has a bare concrete floor but wooden fame, tiled roof .. no
other services ... just a couple of sockets & lights.
So will be running as advised 2C SWA cable out to the building ...

If I fed this via 30mA RCD protection form the house .. (either existing CU
or a new feed to a new small RCD CU off the 100A switch fuse) ... then am
I Ok to export the earth to the garage ?
Under fault conditions the SWA cable is RCD protected .. not just
outbuilding wiring.
I could then just use a small CU in the garage with no local RCD.

Although I can happily install a local earth rod & cable at outbuilding ...
I have a roll of 16mm2 earth cable spare.

I have put what I think are the 2 options on this sketch
http://tinyurl.com/59pw8h

.... is either wrong or either preferred ?

Andy Wade wrote:

If the outbuilding is to be separately TT-earthed then, as you say,
earth the armour at the house end only. Isolate and insulate it at the
far end using an insulating gland (expensive) or use a big plastic
stuffing gland and heatshrink sleeving. Earth the installation to a

How about a waterproof gland onto a plastic CU in the garage, that way
there is no way to make touch contact with the PME earthed armour of the
cable?



--
Cheers,

John.

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\================================================= ================/

Rick Hughes wrote:

Don't export PME ... to a workshop with a bare concrete floor

Outbuilding has a bare concrete floor but wooden fame, tiled roof .. no
other services ... just a couple of sockets & lights.
So will be running as advised 2C SWA cable out to the building ...

If I fed this via 30mA RCD protection form the house .. (either existing
CU or a new feed to a new small RCD CU off the 100A switch fuse) ...
then am I Ok to export the earth to the garage ?

The RCD does not really have any bearing on the risk in this case -
since under fault conditions it will not open the earth connection. The
concern with PME is that in the event of a fault such as a disconnected
PEN conductor (i.e. combined earth and neutral) provided by your
supplier, your earthed metalwork could rise in voltage. This in itself
is accceptable if you can maintain an equipotential bonded zone such
that you can't expose yourself to a dangerous potential differences
between the elevated earth and some external earth reference.

If your outbuilding allows easy access to an independent earth
reference, then you either have to include that in your equipotential
bonding (back to separate protective conductor or large SWA again), or
switch to TT for the outbuilding.

The other consideration is the one Andy mentioned about use of class 1
appliances outside. With a garage there is always the danger that
someone will plug in such a device - say a vacuum cleaner to take out to
a car etc. So no matter how carefully you have preserved the
equipotential zone in the garage, you can't stop someone exporting the
earth to somewhere outside that zone via an appliance.

Under fault conditions the SWA cable is RCD protected .. not just
outbuilding wiring.
I could then just use a small CU in the garage with no local RCD.

You lose the discrimination in the garage (which may or may not be an
issue), but more to the point you don't add much protection to the
submain since it will have adequate earth fault protection by virtue of
its PME head end.

Although I can happily install a local earth rod & cable at outbuilding
... I have a roll of 16mm2 earth cable spare.

I have put what I think are the 2 options on this sketch
http://tinyurl.com/59pw8h

... is either wrong or either preferred ?

First one has the problem described wrt to the exported earth and
maintaining equipotential zones.

The second would be my preferred of the two... (if you want to get posh,
you could skip the RCD in the garage CU and use two RCBOs instead).


--
Cheers,

John.

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\================================================= ================/

John Rumm wrote:

[Big snip - all agreed]

The other consideration is the one Andy mentioned about use of class 1
appliances outside. With a garage there is always the danger that
someone will plug in such a device - say a vacuum cleaner [...]

Don't think I've ever seen a Class 1 vacuum cleaner. Most portable
appliances you'd want to use outside are Class 2 in fact, so this
consideration is perhaps a bit theoretical. Nevertheless it is a
consideration.

First one has the problem described wrt to the exported earth and
maintaining equipotential zones.

Which may or may not be significant, depending on circumstances. The
bare concrete floor though inclines me to prefer the second (TT) option.
There's also the disadvantage that an RCD trip in the garage means a
walk back to the house to reset it.

The second would be my preferred of the two...

Yes _BUT_ as drawn it's not acceptable with the house on a temporary TT
supply. An earth fault on the submain cable is unprotected (Zs much to
high to blow the 32 A fuse) and if it occurred all the earthing would
sit up at 230 V waiting to bite you. There needs to be a temporary RCD
at the house end (ideally a 100 mA delayed action one).

--
Andy

John Rumm wrote:

How about a waterproof gland onto a plastic CU in the garage, that way
there is no way to make touch contact with the PME earthed armour of the
cable?

That's what I meant really - where the waterproof gland is an all
plastic one, something like
http://www.lapplimited.com/14/en/bra...opR/index.html.
And I'd still put some heatshrink over the cable to dress the end where
the armour has been cut off flush with the sheath (this is inside the
CU, of course).

A brass SWA gland wouldn't be acceptable since it's quite easy to pull
the PVC sleeve down and make contact with the metal body which is
connected to the armour.

--
Andy

Andy Wade wrote:
John Rumm wrote:

[Big snip - all agreed]

The other consideration is the one Andy mentioned about use of class 1
appliances outside. With a garage there is always the danger that
someone will plug in such a device - say a vacuum cleaner [...]

Don't think I've ever seen a Class 1 vacuum cleaner. Most portable
appliances you'd want to use outside are Class 2 in fact, so this
consideration is perhaps a bit theoretical. Nevertheless it is a
consideration.

Was about to say "I have", but that was a Hoover Senior about 20 years
ago... and it was not exactly new then! ;-)

First one has the problem described wrt to the exported earth and
maintaining equipotential zones.

Which may or may not be significant, depending on circumstances. The
bare concrete floor though inclines me to prefer the second (TT) option.
There's also the disadvantage that an RCD trip in the garage means a
walk back to the house to reset it.

Yes good point. I used to have an outbuilding supply like that (well I
suppose I have again now - having fixed it once at the old house, I get
to do it all over at the new one) and it was a PITA if you did get a trip.

The second would be my preferred of the two...

Yes _BUT_ as drawn it's not acceptable with the house on a temporary TT
supply. An earth fault on the submain cable is unprotected (Zs much to
high to blow the 32 A fuse) and if it occurred all the earthing would
sit up at 230 V waiting to bite you. There needs to be a temporary RCD
at the house end (ideally a 100 mA delayed action one).

Yes well spotted - I was forgetting we were describing the future supply
rather than the current situation.

(I would still go TT on the outbuilding, and if need be run from a non
time delayed RCD at the head end and just accept the lack of
discrimination while the supply is still "temporary". Assuming the
switch at the head end is in a normal DIN enclosure then swapping the
switch for a RCD would probably be simplest)

--
Cheers,

John.

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Andy Wade wrote:
John Rumm wrote:

How about a waterproof gland onto a plastic CU in the garage, that way
there is no way to make touch contact with the PME earthed armour of
the cable?

That's what I meant really - where the waterproof gland is an all
plastic one, something like
http://www.lapplimited.com/14/en/bra...opR/index.html.
And I'd still put some heatshrink over the cable to dress the end where
the armour has been cut off flush with the sheath (this is inside the
CU, of course).

Those are cheap enough at TLC IIRC...

A brass SWA gland wouldn't be acceptable since it's quite easy to pull
the PVC sleeve down and make contact with the metal body which is
connected to the armour.

You could substitute heatshrink for (or place under) the PVC boot - then
it won't be sliding anywhere in a hurry!

--
Cheers,

John.

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"John Rumm" wrote in message
news:taWdnbH82MqiM5fVnZ2dnUVZ8vGdnZ2d@plusnet...
Andy Wade wrote:
John Rumm wrote:

How about a waterproof gland onto a plastic CU in the garage, that way
there is no way to make touch contact with the PME earthed armour of the
cable?

That's what I meant really - where the waterproof gland is an all plastic
one, something like
http://www.lapplimited.com/14/en/bra...opR/index.html.
And I'd still put some heatshrink over the cable to dress the end where
the armour has been cut off flush with the sheath (this is inside the CU,
of course).

Those are cheap enough at TLC IIRC...

A brass SWA gland wouldn't be acceptable since it's quite easy to pull
the PVC sleeve down and make contact with the metal body which is
connected to the armour.

You could substitute heatshrink for (or place under) the PVC boot - then
it won't be sliding anywhere in a hurry!




Guys appreciate your help (and patience) ... let's see if I have understood.

I earth the armour wires of cable at house end, and totally insulated armour
wires at outbuilding (plastic gland)
Install an earth rod and use that to supply earth to the out building.
(making that a TT installation)
I fit a 30mA RCD in outbuilding to protect all circuits there (or at least
AC outlets)

I then feed the cable at house end via a new sw fuse and 100mA RCD .. to
provide fault current protection of the cable itself.
or I could use an RCBO to combine fuse & RCD protection.
http://tinyurl.com/5zd73z


When Leccy board do finally change me to PME proper, I am assuming I can
leave the install as is ?

Just for a further option could I take the feed at house from a spare 30mA
protected way in consumer unit .... and avoid need for the 100mA RCD.
.... if this is OK (and can't see a reason why not) ... do I still need a
separte RCD in outbuilding ?
I can live without the discrimination. http://tinyurl.com/5kcsjc
... on the this option I have drawn a DP sw ... this is to give me a place
to easily isolate the 'cable' and also easily terminate the armour wires, I
would use the suggested option of.... http://tinyurl.com/57jmud

In both cases am I right that I still need the RCD in the outbuilding to
provide local protection to sockets ?


I had some problem with eSnips .. so also uploaded a combined sketch ...
http://tinyurl.com/6ovfum

On Apr 19, 9:16*pm, John Rumm wrote:
How about a waterproof gland onto a plastic CU in the garage, that way
there is no way to make touch contact with the PME earthed armour of the
cable?

Comment about using non swa glands with swa.
- NICEIC fail such installations (then or later PIR)
- BCO visual inspection check for non swa glands (perhaps new
spies :-)

Argument being swa bs type approval requires bs type approved glands
for swa.

For pme-to-tt swa perhaps consider swa glands into plastic box;
type-approval of swa maintained, but house earth is not exported.

Just a comment.

On 20 Apr, 16:37, wrote:
On Apr 19, 9:16*pm, John Rumm wrote:

How about a waterproof gland onto a plastic CU in the garage, that way
there is no way to make touch contact with the PME earthed armour of the
cable?

Comment about using non swa glands with swa.
- NICEIC fail such installations (then or later PIR)
- BCO visual inspection check for non swa glands (perhaps new
spies :-)

Argument being swa bs type approval requires bs type approved glands
for swa.

For pme-to-tt swa perhaps consider swa glands into plastic box;
type-approval of swa maintained, but house earth is not exported.

Just a comment.



Fair comment ... good to know
I'll terminate using standard brass glands, in a plastic box in the
outbuilding ... and insulate the gland, probably with industrial
heatshrink over the normal plastic shround.

Rick Hughes wrote:

Guys appreciate your help (and patience) ... let's see if I have
understood.

I earth the armour wires of cable at house end, and totally insulated
armour wires at outbuilding (plastic gland)

yup

Install an earth rod and use that to supply earth to the out building.
(making that a TT installation)

yup

I fit a 30mA RCD in outbuilding to protect all circuits there (or at
least AC outlets)

You will need RCD protection for all circuits - including lights -
since the earth fault loop impedance may be too high to open a MCB on an
earth fault in the garage. You could do this with one 30mA one if the
loss of lights on a trip is acceptable, else use individual RCBOs.

I then feed the cable at house end via a new sw fuse and 100mA RCD .. to
provide fault current protection of the cable itself.

100mA with time delay... like:

http://www.tlc-direct.co.uk/Products/MK6980.html

Otherwise you won't be able to predict which will trip in the event of a
genuine fault.

or I could use an RCBO to combine fuse & RCD protection.
http://tinyurl.com/5zd73z

Yup

When Leccy board do finally change me to PME proper, I am assuming I can
leave the install as is ?

You can. You would just have more earth fault protection on the submain
than would actually be required.

Just for a further option could I take the feed at house from a spare
30mA protected way in consumer unit .... and avoid need for the 100mA RCD.
... if this is OK (and can't see a reason why not) ... do I still need a
separte RCD in outbuilding ?

You could do this, and you would not need the separate RCD in the
outbuilding. However you get no discrimination again, and this time you
have to walk back to the house to reset it.

I can live without the discrimination. http://tinyurl.com/5kcsjc
... on the this option I have drawn a DP sw ... this is to give me a
place to easily isolate the 'cable' and also easily terminate the armour
wires, I would use the suggested option of.... http://tinyurl.com/57jmud

In both cases am I right that I still need the RCD in the outbuilding to
provide local protection to sockets ?

Not if the submain has 30mA RCD protection at the head end. Its the
cheapest but least elegant way of doing it really.

I had some problem with eSnips .. so also uploaded a combined sketch ...
http://tinyurl.com/6ovfum

Top piccie is ok, bottom one does not need the RCD in the garage. (if
you put it in, no harm would come, but you could find the RCD at either
end could trip (or both) on a fault)


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

wrote:
On Apr 19, 9:16 pm, John Rumm wrote:
How about a waterproof gland onto a plastic CU in the garage, that way
there is no way to make touch contact with the PME earthed armour of the
cable?

Comment about using non swa glands with swa.
- NICEIC fail such installations (then or later PIR)
- BCO visual inspection check for non swa glands (perhaps new
spies :-)

Argument being swa bs type approval requires bs type approved glands
for swa.

To clarify, I was not suggesting use of a non SWA gland - but use of an
exterior "3 part" one one even though it would not be required for its
waterproof characteristics. (having said that many interior ones come
with the PVC boot anyway).

For pme-to-tt swa perhaps consider swa glands into plastic box;
type-approval of swa maintained, but house earth is not exported.

However this does seem to be a case of being between a rock and a hard
place... the brass gland will make the PME earth accessible in the
outbuilding (albeit will very limited contact opportunity since I doubt
many people spend much time fondling their glands in the garage). Is
there a SWA type approval?




--
Cheers,

John.

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

On 20 Apr, 21:27, John Rumm wrote:
wrote:
On Apr 19, 9:16 pm, John Rumm wrote:
How about a waterproof gland onto a plastic CU in the garage, that way
there is no way to make touch contact with the PME earthed armour of the
cable?

Comment about using non swa glands with swa.
- NICEIC fail such installations (then or later PIR)
- BCO visual inspection check for non swa glands (perhaps new
spies :-)

Argument being swa bs type approval requires bs type approved glands
for swa.

To clarify, I was not suggesting use of a non SWA gland - but use of an
exterior "3 part" one one even though it would not be required for its
waterproof characteristics. (having said that many interior ones come
with the PVC boot anyway).

For pme-to-tt swa perhaps consider swa glands into plastic box;
type-approval of swa maintained, but house earth is not exported.

However this does seem to be a case of being between a rock and a hard
place... the brass gland will make the PME earth accessible in the
outbuilding (albeit will very limited contact opportunity since I doubt
many people spend much time fondling their glands in the garage). Is
there a SWA type approval?

--
Cheers,

John.

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


I haven't fondled my glands in the garage for a long time :-0

Thnaks for the help ... at least I can run the cable in now and close
the trench.

In article ,
writes:
On Apr 19, 9:16*pm, John Rumm wrote:
How about a waterproof gland onto a plastic CU in the garage, that way
there is no way to make touch contact with the PME earthed armour of the
cable?
Comment about using non swa glands with swa.
- NICEIC fail such installations (then or later PIR)
- BCO visual inspection check for non swa glands (perhaps new
spies :-)
Argument being swa bs type approval requires bs type approved glands
for swa.

That's most likely to ensure a good connection to the armour,
which is specifically not wanted in this case.

For pme-to-tt swa perhaps consider swa glands into plastic box;
type-approval of swa maintained, but house earth is not exported.
Just a comment.

I would not use a metal SWA gland at all in this instance.
If you want to use a gland, use a plastic one. However it
no more needs a gland than any of the other cabling going
into the CU. Cut ends of the armour need insulating though,
and a plastic gland could be a good place to have them.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Apr 20, 10:43 pm, (Andrew Gabriel)
wrote:
In article ,
writes:
Argument being swa bs type approval requires bs type approved glands
for swa.

That's most likely to ensure a good connection to the armour,
which is specifically not wanted in this case.

Indeed - and agreed,
however it is one nit-picked area.


1. swa armour cut outside enclosure, heatshrink armour, stuffing gland
over bedding

Favoured to stop PME earth appearing inside same enclosure as TT.

arguments against...
a) swa bedding not intended to be exposed outside enclosure (not
sheath)
b) swa bedding not intended to be clamped by stuffing gland (not
sheath)
c) swa must be terminated by swa gland at entry to enclosure citing a)
b)
d) use of non-swa gland exposes bedding to cut armour on cable
movement/vibration

Specific example of d) was 3-core 4mm - bedding is p*ss thin against
cut armour.


2. swa armour cut inside enclosure, stuffing gland over sheath,
heatshrink armour

arguments against...
a-d) deviations no longer apply,
unfortunately PME earth now inside same enclosure as TT (same as
proper swa gland)


3. swa into swa-gland on plastic box (PME termination box) with swa
bedding routing on through box via male/bush into TT install box.

arguments against...
a-d) deviations no longer apply,
PME & TT earths separated by enclosure.
Unfortunately your swa-gland has a brass body at PME potential
separated by the plastic gland shroud. Fine, until the event of host
PME losing its neutral, whereupon that brass body becomes 240V.

Hence the desire for plastic gland.
Just a comment re some nit-pickers go ape seeing anything but swa-
gland on swa.


Aside, if TT end remotely wet use plastic rotary 1P/3P+N IP65 isolator
(DIN cpd enclosure is high IP-rated until you open the door to isolate
something or reset a CPD). Easily padlocked off if fixed rotary tools
anywhere, kids about, sawing your sister in half gets messy.

wrote:

1. swa armour cut outside enclosure, heatshrink armour, stuffing gland
over bedding

FAOD I wasn't for a moment suggesting that.

arguments against...
[...]
b) swa bedding not intended to be clamped by stuffing gland

True, although the situation is little different from the use of a
stuffing gland to anchor a flexible cord.

2. swa armour cut inside enclosure, stuffing gland over sheath,
heatshrink armour

That is what I was suggesting, and can't really see any problem with.

unfortunately PME earth now inside same enclosure as TT (same as
proper swa gland)

So what? Which regulation(s) in BS 7671 does that violate?

- It's inside an enclosure only accessible with the use of a tool, so
basic (direct contact) protection is achieved.

- Nothing is connected to it.

- It's anchored by the gland so can't move around and short to anything.

- In addition to the above three points you've insulated it with
heatshrink. That's site-applied insulation I suppose, but it would seem
OTT to suggest it needs testing.

- The neutral incomer is also inside the enclosure and that's
electrically the same point, and would be just as 'live' in the event of
an o/c neutral in the DNO's network.

3. swa into swa-gland on plastic box (PME termination box) with swa
bedding routing on through box via male/bush into TT install box.
[...]
Unfortunately your swa-gland has a brass body at PME potential
separated by the plastic gland shroud. Fine, until the event of host
PME losing its neutral, whereupon that brass body becomes 240V.

Agreed: unsatisfactory, since the shroud can be removed without the use
of a tool; also the creepage & clearance distance where the shroud abuts
the box is inadequate.

Hence the desire for plastic gland.
Just a comment re some nit-pickers go ape seeing anything but swa-
gland on swa.

I don't doubt that, but they must be able to justify their decisions by
reference to BS 7671. What does the NICEIC technical manual have to say
on the subject?

--
Andy

On Apr 22, 12:40 am, Andy Wade wrote:
wrote:
1. swa armour cut outside enclosure, heatshrink armour, stuffing gland
over bedding

FAOD I wasn't for a moment suggesting that.

Of course, I used "1." to show how they suggested "2." & then "3.".


2. swa armour cut inside enclosure, stuffing gland over sheath,
heatshrink armour

That is what I was suggesting, and can't really see any problem with.

Neither can I and it is common in industry.


unfortunately PME earth now inside same enclosure as TT (same as
proper swa gland)

So what? Which regulation(s) in BS 7671 does that violate?

None, I could not find anything either.
That inspector insisted on swa gland for swa into plastic box.
Other contractors insisted "rectifying" to swa gland into plastic box.

The belief being that the plastic enclosure "stops PME contact".
They did not consider the "shroud does not require tool for removal".


3. swa into swa-gland on plastic box (PME termination box) with swa
bedding routing on through box via male/bush into TT install box.
[...]
Unfortunately your swa-gland has a brass body at PME potential
separated by the plastic gland shroud. Fine, until the event of host
PME losing its neutral, whereupon that brass body becomes 240V.

Agreed: unsatisfactory, since the shroud can be removed without the use
of a tool; also the creepage & clearance distance where the shroud abuts
the box is inadequate.

Exactly. Shroud removal exposes PME earth to anyone in the TT install.

I suspect miss-application of 511-01-01 re intended purpose.
Yes the intended purpose of an swa gland IS to terminate swa.
However a more important need is preventing PME sitting on the outside
of your enclosure in a TT install, which necessitates a plastic gland.



Hence the desire for plastic gland.
Just a comment re some nit-pickers go ape seeing anything but swa-
gland on swa.

I don't doubt that, but they must be able to justify their decisions by
reference to BS 7671. What does the NICEIC technical manual have to say
on the subject?

Unknown, it would be interesting to find out.

My suspicion is that they would say the plastic gland ("2.") complies.
I hope they would also state that "3." fails for the reason given.

A case of using a plastic gland, but if challenged cite the shroud.

wrote in message
...
On Apr 22, 12:40 am, Andy Wade wrote:
wrote:
1. swa armour cut outside enclosure, heatshrink armour, stuffing gland
over bedding

FAOD I wasn't for a moment suggesting that.

Of course, I used "1." to show how they suggested "2." & then "3.".


2. swa armour cut inside enclosure, stuffing gland over sheath,
heatshrink armour

That is what I was suggesting, and can't really see any problem with.

Neither can I and it is common in industry.


unfortunately PME earth now inside same enclosure as TT (same as
proper swa gland)

So what? Which regulation(s) in BS 7671 does that violate?

None, I could not find anything either.
That inspector insisted on swa gland for swa into plastic box.
Other contractors insisted "rectifying" to swa gland into plastic box.

The belief being that the plastic enclosure "stops PME contact".
They did not consider the "shroud does not require tool for removal".

Just put the whole thing in a bigger box and screw the lid down.. then it
needs a tool. ;-|

wrote in message
...



I'm not really sure where this leaves me ...It seems I can't use a plastic
gland as it will not meet BCO requirements ..
if I use a brass gland it is potentially dangerous unless the connection is
modified.

a) Terminate using a brass gland .. and if I then heat shrink a full
industrial sleeve over gland - is that 'acceptable' (better than push fit
pvc sleeve)
- and accept armour wires are within enclosure - but not terminated

b)Terminate using brass gland .. but making connection on top bedding not
the wires - is that 'acceptable' - seems poor practice.

b) Terminate with a plastic Gland



Or perhaps a solution is terminate fully as normal but within a separate
plastic box (that needs tools to open) and then take only L&N into the CU.
Presumably this meets BCO requirements and is also safe ?

Terminate as A.Wade suggests with a plastic gland (listed as "2." in
my comment).

In the future if anyone says you should use a "proper SWA gland in
plastic box" point out to them that doing so would leave a "non-tool
removable shroud as the only separator between a TT install & PME
brass gland underneath".
Stick that on a bit of paper in the box - just something to know if
someone demands an SWA gland :-) No chance of it, but at least you are
prepared to send them away to actually think rather than kneejerk.


Some installation comments...

Leave a "repair loop" in your swa
- that way you can redo terminations or gland without having to
replace a cable

Cable should be at a depth appropriate for ground usage
- ploughed field 1.5m or more, typical domestic 0.45m

Cable should be laid in a suitably prepared trench
- trench free from large stones, cable laid on a bed of riverwashed
sand
- 150mm of riverwashed sand above, then yellow cable marking tape,
then backfill

Cable route should be documented somewhere

Watch cutting bedding around insulation, 4mm 3-core is often very thin
above the cores
- easy to nick the insulation which will fail a visual inspection if
not an insulation resistance test also
- it is for this reason that repair loops are a very good idea

Nuffin to it, its the digging that will hurt the following morning.

Rick Hughes wrote:

Or perhaps a solution is terminate fully as normal but within a separate
plastic box (that needs tools to open) and then take only L&N into the CU.
Presumably this meets BCO requirements and is also safe ?

Note that "BCO requirements" will vary with the BCO. So you may as well
do it according to BS7671 and worry about what any BCO might say later
(and if they want to argue, ask for supporting paragraphs from 7671).

--
Cheers,

John.

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

"John Rumm" wrote in message
news:hvidnbOA7JgpPZLVnZ2dneKdnZydnZ2d@plusnet...

Note that "BCO requirements" will vary with the BCO. So you may as well do
it according to BS7671 and worry about what any BCO might say later (and
if they want to argue, ask for supporting paragraphs from 7671).

--
Cheers,

John.



which is what ? .... terminate is plastic gland or metal ? .... not being
facetious, just want to get it right.