I'm going to be installing a new sub-main using 25mm 3-core SWA. As
SWA is an absolute pig to work with I'm probably going to need to
terminate the SWA before it enters the final enclosure/CU.

At one end, this is no problem - I'm going to use a metal adaptable
box, in an accessible location, in a safe zone (above the CU).

At the other end I have more of a challenge. I want to terminate the
SWA at another metal adaptable box above the front door. I then want
to run something slighty easier to deal with round a slightly tighter
route. The will be visible (i.e surface mounted).

Does anyone have any useful suggestion about how I can do this? I can
probably route each core within the SWA individually, but not the
internal (i.e. non armoured sheath) 3 core together. Is it permitted
to run the cores indivudally like this, or do I need to manually sheath
each one? If so, any suggestions as to what I should use?

Thanks,
Piers

Piers Finlayson wrote:

At the other end I have more of a challenge. I want to terminate the
SWA at another metal adaptable box above the front door. I then want to
run something slighty easier to deal with round a slightly tighter
route. The will be visible (i.e surface mounted).

Does anyone have any useful suggestion about how I can do this? I can
probably route each core within the SWA individually, but not the
internal (i.e. non armoured sheath) 3 core together. Is it permitted
to run the cores indivudally like this, or do I need to manually sheath
each one? If so, any suggestions as to what I should use?

Could you switch to 25mm meter tails and a suitably sized earth cable?

On Dec 6, 12:57*pm, Piers Finlayson wrote:
I'm going to be installing a new sub-main using 25mm 3-core SWA. *As
SWA is an absolute pig to work with I'm probably going to need to
terminate the SWA before it enters the final enclosure/CU.

I presume you do need 25mm - re distance (voltage drop to lights) or
current demands?
You can not use the DNO main fuse to provide protection to your sub-
main, which in turn means you do not have to size according to it -
ie, if you want 16A at a shed 30m away then 6mm will be perfectly
fine.

The cores in 25mm are shaped and the bending radius for 25mm SWA is
"big" as you have probably found. There is also a min temperature for
installation of SWA (and most cables for that matter).

Does anyone have any useful suggestion about how I can do this? *I can
probably route each core within the SWA individually, but not the
internal (i.e. non armoured sheath) 3 core together. *Is it permitted *
to run the cores indivudally like this, or do I need to manually sheath
each one? *If so, any suggestions as to what I should use?

You can not run bare cores except in say round flexible conduit (25mm
or 32mm) or PVC trunking, which would need to be quite big anyway.

25mm H07RNF 3-core exists, is quite tough, waterproof, UV proof, very
flexible. It is almost certainly smaller diameter than say 3 25mm
cores when stuck in trunking or flexible conduit and somewhat more
forgiving re route.

On 06/12/10 13:05, js.b1 wrote:
On Dec 6, 12:57 pm, Piers wrote:
I'm going to be installing a new sub-main using 25mm 3-core SWA. As
SWA is an absolute pig to work with I'm probably going to need to
terminate the SWA before it enters the final enclosure/CU.

I presume you do need 25mm - re distance (voltage drop to lights) or
current demands?
You can not use the DNO main fuse to provide protection to your sub-
main, which in turn means you do not have to size according to it -
ie, if you want 16A at a shed 30m away then 6mm will be perfectly
fine.

The cores in 25mm are shaped and the bending radius for 25mm SWA is
"big" as you have probably found. There is also a min temperature for
installation of SWA (and most cables for that matter).

Does anyone have any useful suggestion about how I can do this? I can
probably route each core within the SWA individually, but not the
internal (i.e. non armoured sheath) 3 core together. Is it permitted
to run the cores indivudally like this, or do I need to manually sheath
each one? If so, any suggestions as to what I should use?

You can not run bare cores except in say round flexible conduit (25mm
or 32mm) or PVC trunking, which would need to be quite big anyway.

25mm H07RNF 3-core exists, is quite tough, waterproof, UV proof, very
flexible. It is almost certainly smaller diameter than say 3 25mm
cores when stuck in trunking or flexible conduit and somewhat more
forgiving re route.

For conduit - I would recommend Kopex pliable 32mm. It's all plastic (no
earthing issues), bloody tough, doesn't look bad (black, smooth-ish
*and* smooth bored, could be painted) and the adaptors make off to IP65.
The OP could certainly run the single insulated cores of SWA through
that provided the conduit is surface or otherwise protected (usual IEE
regs about buried non RCD protected cables).

I used some for my tails to protect them going through a roof void and
down over the wall plate then into the meter box outside with a
waterproof connection. Thoroughly met with approval from EDF when they
put my cutout fuse back.

RS sell it.

You can thread a couple of 25mm2 (prob 3 at a pinch) through if it has
mild bends, otherwise make it all up on the flat (straight) then install
and form as a pre-assembled bundle.

--
Tim Watts

On 06/12/10 13:46, Tim Watts wrote:
For conduit - I would recommend Kopex pliable 32mm. It's all plastic (no
earthing issues), bloody tough, doesn't look bad (black, smooth-ish
*and* smooth bored, could be painted) and the adaptors make off to IP65.
The OP could certainly run the single insulated cores of SWA through
that provided the conduit is surface or otherwise protected (usual IEE
regs about buried non RCD protected cables).

I used some for my tails to protect them going through a roof void and
down over the wall plate then into the meter box outside with a
waterproof connection. Thoroughly met with approval from EDF when they
put my cutout fuse back.

RS sell it.

You can thread a couple of 25mm2 (prob 3 at a pinch) through if it has
mild bends, otherwise make it all up on the flat (straight) then install
and form as a pre-assembled bundle.


Here's some:

http://photos.dionic.net/v/public/bu..._0004.jpg.html

http://photos.dionic.net/v/public/bu...80707.jpg.html


--
Tim Watts

Re photos, nicely done.

25mm is a big sub-main so I wonder if the OP is just going for too big
a cable... unless it is very very long... in which case going outside
the limit for lighting (say) is possible as a noted departure from
BS7671.

25mm H07RNF is £8.61/m ex VAT from one source, but I suspect a similar
diameter (32mm).

On 06/12/10 15:45, js.b1 wrote:
Re photos, nicely done.

25mm is a big sub-main so I wonder if the OP is just going for too big
a cable... unless it is very very long... in which case going outside
the limit for lighting (say) is possible as a noted departure from
BS7671.

25mm H07RNF is £8.61/m ex VAT from one source, but I suspect a similar
diameter (32mm).

I probably wouldn't get too hung up on volt drops if the supply nominal
is good to start with (like ~240V) - if the OP had (paid) the supplier
to move the meter, they'd probably run a similar length of similar or
smaller CSA concentric and achieve exactly the volt drop (but outside
the remit of the IEE regs of course!). The point being symmetry and a
degree of common sense. I'd aim to minimise the volt drops as far as
practical though.

I would personally care that (if it is a long, eg 3m) run, that I had a
switchfuse at the meter end, and the SWA was sufficient for carrying the
earthing conductor *and* was capable of blowing the OP's fuse
(switchfuse, not cutout) in the 5 seconds required for a distribution
circuit - on both a L-E and L-N fault.

--
Tim Watts

On 2010-12-06 12:57:01 +0000, Piers Finlayson said:

I'm going to be installing a new sub-main using 25mm 3-core SWA. As
SWA is an absolute pig to work with I'm probably going to need to
terminate the SWA before it enters the final enclosure/CU.

At one end, this is no problem - I'm going to use a metal adaptable
box, in an accessible location, in a safe zone (above the CU).

At the other end I have more of a challenge. I want to terminate the
SWA at another metal adaptable box above the front door. I then want
to run something slighty easier to deal with round a slightly tighter
route. The will be visible (i.e surface mounted).

Does anyone have any useful suggestion about how I can do this? I can
probably route each core within the SWA individually, but not the
internal (i.e. non armoured sheath) 3 core together. Is it permitted
to run the cores indivudally like this, or do I need to manually sheath
each one? If so, any suggestions as to what I should use?

Thanks,
Piers

In response to other posters responses (for which thanks):

I strictly don't need 25mm - I'm going for 3 core 25mm because
- it has been suggested that the DNO might frown on 16mm should
they ever see it (I am essentially extending the supply to a new
location, and am aware that I need a CU within 2/3m of the meter) €“ see
http://groups.google.com/group/uk.d-...d2453ee15affe2
- I want a 16mm earth, and IIRC the amour of 25mm SWA is about 13mm
copper CSA equiv €“ so cant use 2 core
- it allows headroom for future expansion (i.e. moving up to a 100A
supply), where 16mm is marginal.

Ive even toyed with 4 core 25mm for possible future upgrade to a three
phase. But not sure I need to plan for that much power!

My supply is actually at around 255V. Yes, I know this is over spec,
and something I may get the DNO to sort in due course.

I like the meter tail idea, given I know I can work 25mm tails OK in
the space I have. How would you recommend I connect the line and
neutral within a small space? Is a Henley block a sensible option or
are there better options using small space?

Piers Finlayson wrote:

I like the meter tail idea, given I know I can work 25mm tails OK in the
space I have. How would you recommend I connect the line and neutral
within a small space? Is a Henley block a sensible option or are there
better options using small space?

I know this is 63A and you were planning ahead for 100A

http://www.tlc-direct.co.uk/Products/CSWHT63.html

but it looks a *bit* more decor friendly than the typical red/yellow
rotary isolators, don't know if rotary ones include earth block either.

On 06/12/10 20:01, Andy Burns wrote:
Piers Finlayson wrote:

I like the meter tail idea, given I know I can work 25mm tails OK in the
space I have. How would you recommend I connect the line and neutral
within a small space? Is a Henley block a sensible option or are there
better options using small space?

I know this is 63A and you were planning ahead for 100A

http://www.tlc-direct.co.uk/Products/CSWHT63.html

but it looks a *bit* more decor friendly than the typical red/yellow
rotary isolators, don't know if rotary ones include earth block either.


And if terminating SWA into a plastic enclosure, the OP would be advised
to use these on the gland:

http://www.tlc-direct.co.uk/Main_Ind...uts/index.html

Can't trust nut tightness on a banjo tag when bolted though compressible
plastic.

I'm sure the OP is also aware, but don't forget an external grade SWA
gland for outside use (prob a good idea even in a meter box).

--
Tim Watts

On 06/12/10 19:39, Piers Finlayson wrote:
On 2010-12-06 12:57:01 +0000, Piers Finlayson said:

I'm going to be installing a new sub-main using 25mm 3-core SWA. As
SWA is an absolute pig to work with I'm probably going to need to
terminate the SWA before it enters the final enclosure/CU.

At one end, this is no problem - I'm going to use a metal adaptable
box, in an accessible location, in a safe zone (above the CU).

At the other end I have more of a challenge. I want to terminate the
SWA at another metal adaptable box above the front door. I then want
to run something slighty easier to deal with round a slightly tighter
route. The will be visible (i.e surface mounted).

Does anyone have any useful suggestion about how I can do this? I can
probably route each core within the SWA individually, but not the
internal (i.e. non armoured sheath) 3 core together. Is it permitted
to run the cores indivudally like this, or do I need to manually
sheath each one? If so, any suggestions as to what I should use?

Thanks,
Piers

In response to other posters responses (for which thanks):

I strictly don't need 25mm - I'm going for 3 core 25mm because
- it has been suggested that the DNO might frown on 16mm should they
ever see it (I am essentially extending the supply to a new location,
and am aware that I need a CU within 2/3m of the meter) €“ see
http://groups.google.com/group/uk.d-...d2453ee15affe2

Technically the line conductor size isn't their concern once it's past
your first fuse assuming it is fused correctly for the length/capacity
etc. But they might show an interest in an undersized earth - I would
personally use a 3rd core for earth here due to the onerous requirements
on the main earthing conductor - parallel with the armour on both ends.

- I want a 16mm earth, and IIRC the amour of 25mm SWA is about 13mm
copper CSA equiv €“ so cant use 2 core
- it allows headroom for future expansion (i.e. moving up to a 100A
supply), where 16mm is marginal.

All sounds very sensible. I went through all the calculations when I was
wondering whether to do something similar - in the end I compromised on
the CU position and got it close enough to the meter to satisfy the 3m rule.

Ive even toyed with 4 core 25mm for possible future upgrade to a three
phase. But not sure I need to plan for that much power!

My supply is actually at around 255V. Yes, I know this is over spec, and
something I may get the DNO to sort in due course.

I like the meter tail idea, given I know I can work 25mm tails OK in the
space I have. How would you recommend I connect the line and neutral
within a small space? Is a Henley block a sensible option or are there
better options using small space?

[Not and expert mode on...]

Big metal crimps and suitable over insulation in an enclosure?

Or http://www.tlc-direct.co.uk/Products/PRCON4.html

I must admit - I'm not totally convince by those sleeves in the link,
but Pratley are a good make which makes me think they must know what
they are doing.

Another option could be to use a 100A DP main switch as a terminal
mechanism - ie a tiny 4-way CU perhaps. Also, possibly some big *******
DIN terminals (try RS) in a similar enclosure for same without switch.

Not sure what I would use - those are just there for initial ideas...






--
Tim Watts

That referenced isolator is a european design and I have a suspicion
it permits the removal of the lid in the "on" position which may
contravene BS7671. Rotary isolators need to be the oversized enclosure
type to handle SWA, Piranha nut a given in this situation with a
plastic enclosure.

The pratley "grub-screw-in-a-hoop" work with top-hat work fine.
Just tighten them with a decent allen-key, wait a while, then tighten
again because stranded will loosen. Alternatively you can copper-tube
crimp - but it needs a suitable crimp tool and matching crimps which
for 25mm is not so cheap. A klauke k02 is about £80 from Farnell and
the matching butt-crimps are about £12 (you have to use klauke, do not
use any other because they WILL just pull out - UK uses mostly light-
duty crimps compared to EU-land heavy duty). TLC will do matching
crimps & tool, as well any local electrical factor (SWA is one
respected brand, you do not have to go to Cembre although you may find
City Electrical Factors will hire the tool out cheaply and might even
sell a handful of butt-crimps).

Pratley above/under ground boxes use their own gland system, which can
be expensive. I prefer a good CW gland or even E1W which guarantee
water ingress into the enclosure can not go down the cable and rot the
armour on what can be a very expensive cable if long (SiteBox does
E1W, Bicon & CCG are two common makes). Two 20m runs of 25mm (Peak &
E7) are getting on for £400 so the extra for better (E1W) glands is
worth having if water is ever likely to penetrate an outside enclosure
in a rickety garage or such like.

Re sizing cable for 100A not 60A, well perhaps.

Remember a 60A BS1362 fuse will permit 1.6x its rating to be drawn
continuously - that is essentially 100A and why an electric shower
"and everything else" is often run on a 60A fuse without blowing it.
Modern SWA uses XLPE insulation and can thus handle more current than
PVC - although remember most wiring accessories are limited to 70oC
which means derating to PVC. That is unless of course you use higher
temperature wiring accessories re 90oC (which for a sub-main is quite
possible).

On 2010-12-06 21:51:19 +0000, js.b1 said:

That referenced isolator is a european design and I have a suspicion
it permits the removal of the lid in the "on" position which may
contravene BS7671. Rotary isolators need to be the oversized enclosure
type to handle SWA, Piranha nut a given in this situation with a
plastic enclosure.

The pratley "grub-screw-in-a-hoop" work with top-hat work fine.
Just tighten them with a decent allen-key, wait a while, then tighten
again because stranded will loosen. Alternatively you can copper-tube
crimp - but it needs a suitable crimp tool and matching crimps which
for 25mm is not so cheap. A klauke k02 is about £80 from Farnell and
the matching butt-crimps are about £12 (you have to use klauke, do not
use any other because they WILL just pull out - UK uses mostly light-
duty crimps compared to EU-land heavy duty). TLC will do matching
crimps & tool, as well any local electrical factor (SWA is one
respected brand, you do not have to go to Cembre although you may find
City Electrical Factors will hire the tool out cheaply and might even
sell a handful of butt-crimps).

I have access to a heavy duty crimp tool (25mm - 200 odd mm) via work,
but I prefer the idea of the pratley connectors rather than mess around
with crimping. Thanks for the suggestions.

On 06/12/10 21:51, js.b1 wrote:

The pratley "grub-screw-in-a-hoop" work with top-hat work fine.
Just tighten them with a decent allen-key, wait a while, then tighten
again because stranded will loosen.

That's useful to know. So the "top-hat" fits quite firmly and won't fall
off? That was the only thing I was wondering about...



--
Tim Watts