Electrical cable outside

Hi,
If you wish to run a cable up a wall on the outside of a house, can this be ordinary T&E inside metal piping or conduit? Or does it have to be armoured cable as well?
TIA
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Yes - but SWA is the cheaper option material cost wise - and quicker to install.
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*Never test the depth of the water with both feet.*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

I see dozens of examples of T&E cable surface mounted to exterior walls, mostly above head height for security lights.
Are we saying this should be in trunking? Or armoured?
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Dave - The Medway Handyman
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The Medway Handyman wrote:

Its not UV safe, and so will harden and risks the insulation cracking. Painting it would help, and would a sheltered location.

Either, or use an exterior rated cable like HiTuf
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Cheers,

John.

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Nobody wrote:

Yes... or plastic

No, but you could use that without additional protection.
http://wiki.diyfaq.org.uk/index.php?title=Taking_electricity_outside#Cable_choice
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Cheers,

John.

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http://wiki.diyfaq.org.uk/index.php?title=Taking_electricity_outside#Cable_choice
'Fraid I have to take exception to that article John. If the conduit is to protect the T&E from physical damage, ie, being hit with something then fair enough perhaps, but I really do wish that we could end the myth that ordinary PVC T&E is attacked by UV and becomes brittle and cracks.
This subject came up either last year or the year before on the group and I replied then as I will now. We have a run of approximately 7 metres of 1.0mm T&E clipped directly to the *south facing* (so it's exposed to a lot of sunshine and UV) wall at the back of our house, which feeds an external light. It was installed about 20 years ago now but last year (maybe the year before) I had to unclip it while I did some other, unrelated work, and it was still very flexible, was not in any way brittle, and did not break or crack at all.
After completing what I had to do, it was clipped back up again and is none the worse, either for being moved or for sitting in sunlight for 20 years. So if the OP is asking the question on sunlight/UV grounds alone, I'd say that it can be clipped directly with no need for conduit or capping at all, but if it's in danger of being hit or damaged by something else, then fair enough, use conduit/capping.
John
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John wrote:

...
What you have highlighted is that *your* bit of T&E was fine. I don't think the same can be stated with complete confidence as a general case though.
IME some brands are very much better than others. Generally plasticised PVC will lose plasticiser with UV exposure (which is why most PVC stuff designed for use outside is made from uPVC). However this may not mean that it becomes non-handleable, but just less flexible than it once was.
In Table 3A The OSG states that clipped to an external wall ordinary flat T&E may be ok, although it does also say "protection from direct sunlight may be necessary. Black sheath colour is better for cables in sunlight"
BS7671 says:
"522-11 Solar radiation (AN) and ultra-violet radiation 522-11-01 Where significant solar radiation (AN2) or ultra-violet radiation is experienced or expected, a wiring system suitable for the conditions shall be selected and erected or adequate shielding shall be provided."
(where AN2 refers to the medium band of solar radiation in the range 500 - 700 W/m^2)
In light of the above, and your comments I think it would be appropriate to tone down the recommendations on the wiki a little though. Try this:
http://wiki.diyfaq.org.uk/index.php?title=Taking_electricity_outside#Cable_types
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Cheers,

John.

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http://wiki.diyfaq.org.uk/index.php?title=Taking_electricity_outside#Cable_types
Yes, that's better mate,
cheers,
John
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John Rumm wrote:

There is also the issue of reduction in the current rating of cables being warmed by sunlight. While this can safely be ignored for low-current things like small-scale outside lighting, that wouldn't necessarily be the case for power applications such as sub-mains to outbuildings.
The fact that such cables will probably have been sized on voltage drop rather than current rating may provide some leeway. Nevertheless the matter should be considered in the design. Table 4C1 of BS 7671 applies and common experience suggests that things in the sun can reach temperatures of 50 or 60 deg. (sometimes more). The de-rating factor for 70 deg. rated PVC cables is 0.71 at 50 deg. and 0.50 at 60 deg. For 90 deg. rated XLPE cables the corresponding factors are 0.82 and 0.71 respectively.
If at all possible fix outdoor cables where they will stay out of the full glare of the sun.
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Andy

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On Thu, 22 Nov 2007 11:59:17 +0000, John Rumm

Thanks for all the responses. I should clarify that this would be from the consumer unit on the ground floor and up to the loft to provide a ring main and llighting circuit. I had been told that the "rules" didn't allow it to be bare or in a conduit and the builders wanted to put it down inside the cavity wall - which is now full of insulation from two years back. I couldn't see why conduit wasn't allowed. Mention of NICE (spit) etc.
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Nobody was thinking very hard :

Installation in the cavity wall is not permitted. Can you not find a route up through the inside of the house?
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Regards,
Harry (M1BYT) (L)
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Nobody wrote:

Conduit *is* allowed - as long as one accounts for the current de-rating effect in the circuit designs. Since for 2.5mm^2 T&E this is only a reduction from 27A capacity when clipped direct, to 23A (Table 4D2A) when enclosed in conduit (reference method 3 it should not be an issue for conventional 32A ring circuits unless other de-rating factors come into play.
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Cheers,

John.

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On 22 Nov,

So effectively in conduit or trunking you can only have one 2.5mm^2 or else it is derated below the magical 20A. This seems ludicrous for 4" or even 2" trunking.
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B Thumbs
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Reason is not the size of trunking - but cable separation :-)
Eg, installation Method M1 for cables on surface... o 1 Dia separation, N= 2, Cg = 0.94 o 0 Dia separation, N= 2, Cg = 0.85 -- cables touching on surface
Cable bunching between joists requires Cg = 0.90.
When we ran 8 cables they were arranged in 4 pairs with one of each pair being 1.5mm 6A (Lights Smoke Alarm). Thus 30% cable load allows N=2 cable grouping to be disregarded (N=1).
Each pair ran through a P-clip/screw/wallplug to maintain separation >2D largest cable major axis from the next pair. Bricks too hard for clips, mortar too weak for clips. That way derating was kept to a minimum, buried direct M2.
Physically very tedious, with hindsight it may seem better to use a single 6242Y or SWA to a mini-CU instead. Even 10mm SWA fits thro a standard 20mm backbox hole if you want to mark a route outside zones, min bend radius is handled via bending up the wall on internal corners. Typical problem is you end up routing N cables "back" along the route you took to where needed - so rejected.
Where cables are grouped for short distances you can ignore grouping - basically as you would for a joist width. However it may be wise to assume bunching Cg of 0.90, for domestic usage this should rarely be a problem.
Industrially they (literally) throw CSA at the problem if in supersized trunking or use cable trays accordingly. Cable trays often carry SWA which is XLPE, so absorbs cable derating problems re higher current rating. It is not practical to do that with say XLPE 6242B domestically because the 90oC figure does not apply to fittings. Plus you can not use that figure & route by PVC cables.
The FP200/400 etc concentric cables are popular as they remove the need for armour in some circumstances, so are quicker to fit (altho not cheaper). Unfortunately it seems nearly all are 70oC rated vs SWA XLPE so as a result the "grouping problem absorption" is lost, but since they are smaller than SWA separation increases.
With planning you can avoid most grouping problems. However 24-way MK Grid boxes must be *fun* to do.
--
DB.



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snipped-for-privacy@privacy.net wrote:

Another option would be to run a pair or even three 16A radials for socket provision.
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Cheers,

John.

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As stated you can not run cables in a cavity wall. BS7671 16th OSG specifically refers to this IIRC.
Hituff... o Some NICEIC inspectors dislike it as "h/duty flex" ---- it has stranded core, but so does FP200-Flex ---- FP200-Flex is permitted for fixed wiring apps o Many dislike Hituff gland arrangement ---- outer sheath is *rigid hard plastic* ---- most glands require that rigid outer to be removed ---- so the gland can seal around inner cable bedding ---- some inspectors dislike this as a weak point
They can/often make up regulations as they go or rewrite regulations to meet financial requirements.
Your later post changes your requirements :-) You require a Ring & Lighting circuit in the loft.
This can be achieved in 2 ways... 1. Ring Main & Lighting cables ---- Ring -- 2 runs of FTE-2.5mm (Flat Twin & Earth) ---- Lighting -- 1 run of FTE-1.5mm 2. Distribution Circuit to Mini-CU in the loft ---- Single cable, but probably not using FTE-4.0mm ---- FTE-4.0mm length limited by small 1.5mm CPC (ELFI)
Lighting using 1.5mm allows grouping of the lighting cable to be ignored because 18A maximum fused at 6A is 30%.
Option-1 is difficult... 1.1 Multiple FTE do not fit well in conduit ---- 2x FTE-2.5 & 1x FTE-1.5 really needs 32mm conduit ---- the variety of fittings for 32mm conduit is limited ---- using 1x FTE-4.0 will not work re distance (1.5mm CPC) ---- cable grouping ok (lighting cables <30% max so ignored) ---- bend radius is the challenge here re bundle of FTE 1.2 Multiple 6491X "Singles" are more suited to conduit ---- assuming 5m straight run with 90-degree bends top/bottom ---- 25mm conduit cable factor is 358 (OSG p114 Table 5D) ---- assuming ring & light in 2.5mm 6491X so just 3 cable reels ---- 9x 2.5mm cables have a combined cable factor of 9*30 = 270 ---- combined cable factor (270) is below conduit (358) so ok ---- top/bottom junction box connects to FTE-2.5mm & 1.5mm ---- cable grouping ok (lighting cables <30% max so ignored) 1.3 SWA with 4 cores & CPC (armour) ---- 4-core 2.5mm SWA has o.d. 14.4mm, max in duct 34A ---- high current rating is due to 90oC XLPE insulation vs PVC ---- 2 cores for ring + 2 cores for lighting + armour for earth ---- top/bottom junction box connects to FTE-2.5mm & 1.5mm ---- really need Earthing Nut on both glands for reliable earth ---- label junction box "2 final circuits in SWA, isolate both" ---- cable grouping ok (lighting cables <30% max so ignored) ---- bend radius is 6D or 90mm - take note
Option-2 is a little easier... 2.1 Single FTE can fit ok in conduit with FEW bends ---- 1x FTE-6.0 may fit in 25mm conduit & 2 bends, not easy ---- plenty of fittings for 25mm conduit, black, white ---- FTE-6.0 has a 2.5mm CPC so probably ok (check) ---- Mini-CU in loft w/ 32A MCB & 6A MCB FTE-2.5 & 1.5mm 2.2 Multiple 6491X are more suited to conduit ---- 25mm conduit with 4.0mm singles for Phase/Neutral *&* CPC ---- Mini-CU in loft connects 32A MCB & 6A MCB FTE-2.5 & 1.5mm 2.3 SWA with 2 cores & CPC (armour) ---- 2-core 2.5mm would probably do, 4.0mm preferable ---- bend radius is 6D or 90mm - take note ---- Mini-CU in loft w/ 32A MCB & 6A MCB FTE-2.5 & 1.5mm
I would choose option 1.2... o 25mm black conduit, available in 3m lengths ---- heavy duty type o 25mm black conduit 1-way terminal box (round BESA) ---- rear entry via female bushing to conduit going thro wall ---- PVC glue (solvent) or clear silicone for bushing & conduit ---- rubber gasket under terminal box lid, M4x10 brass screws ---- drill drain hole at the bottom of the bottom conduit box ---- conduit box at each end (top/bottom) o On inside wall deep 2G metal box w/25mm rear hole ---- most 2G boxes lack a rear 25mm hole ---- use flush or surface, plastic or metal "adaptable box" ---- 30A & 15A terminal strips (ideally glass filled nylon) o Feed bottom junction box with 2x FTE-2.5mm & FTE-1.5mm ---- run to dedicated 32A RCBO & 6A MCB in CU o Take top junction box with 2x FTE-2.5mm & FTE-1.5mm ---- remember rubber grommets on all cable entries
www.gil-lec.co.uk will sell you 6491X by the metre, so you need not buy 3x 100m reels of 2.5mm but just the cut lengths of 3x 4.0mm (ring) & 3x 1.5mm (lighting) you require.
Very simple, perfectly acceptable. I fit cable shrouds over the conduit-entry to conduit box just as an extra, it actively prevents any water loading. PVC glue never seals conduit after a while due to the expansion/contraction of plastic (higher than metal), so to be honest a quality flexible silicone can be better.
Had you just required a single cable upstairs... I would suggest FP200 (Firetuf) in white (UV ok). Routinely used for outside power & lighting from M&S to Post Office. Use a waterproof gland to a malleable iron conduit box, they have a thread exit to suit the gland thread. Then a rear hole through the wall to conduit & junction box on the inside. FP200/Firetuff sheath is removed as soon as it enters the gland to turn it into "singles" so as to make the tight turn through the rear exit & through conduit to the jn-box inside. FP200 is a pseudo concentric cable like SWA, very tough outer skin, but no armour (concentric foil under sheath). It is small (8-11mm dia), but subject to 6D bend radius.
The ideal solution is to route indoors.
Failing that, the above option 1.2 is the least messy. A straight conduit between 2x conduit 1-way boxes on a wall in 25mm is discrete and functional. I suspect you will exit the wall quite high, so mechanical protection is less important and heavy duty conduit is actually fine. I would not bother running in steel, if you do: galvanised.
--
DB.



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On Thu, 22 Nov 2007 19:23:23 GMT, "Dorothy Bradbury"
[snip]
Thanks to all for the information and advice. I wanted to confirm I was being told rubbish in the first place. I will look at internal routing as well - looks like the floorboards will be murdered again :-))
Best regards.
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See my updated comment - and do look at floorboards :-)
Option 1.2 4.0+1.5mm is simple, but can get ugly. Just been at a dentist where the plumber went mad with angles/couplings/brackets/standoffs on the outside walls! Adding conduit runs to the mix really puts off buyers.
Cables outside is visually better kept for lights-n-sheds. The Lloyds Building approach does not work on houses.
--
DB.



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To add more detail re option 1.2...
In brief... o Correction for Cable Grouping eliminates some options. o Option 1.1 -- fails re cable grouping o Option 1.2 with 6491X 2.5mm -- fails re cable grouping o Option 1.2 with 6491X 4.0mm -- ok re cable grouping
In detail... o 1.1 - Twin FTE-2.5mm & FTE-1.5mm in 32mm conduit ---- not possible because FTE-2.5 in Method M3 is just 23A ---- lighting cable is disregarded as 30% loading hence N=2 ---- Cg = 0.80 for N=2 (2 cables for each ring leg) ---- 23A x 0.80 = 18.4A *BELOW* the required 20A per-ring-leg ---- Twin FTE-4.0mm would be required, gets chunky o 1.2 - Multiple 6491X "Singles" 2.5mm ---- not possible because 2.5mm in Method M3 is just 24A ---- lighting cable is disregarded as 30% loading hence N=2 ---- Cg = 0.80 for N=2 (2 cables for each ring leg) ---- 24A * 0.80 = 19.2A *BELOW* the required 20A per-ring-leg ---- single 6491X 4.0mm would be required - no problem o 1.2 - Multiple 6491X "Singles" 4.0mm ---- possible because *single* 4.0mm in Method M3 is 32A ---- lighting cable is disregarded as 30% loading hence N=1 ---- Cg = 1.00 for N=1 (1 cable required) ---- 32A * 1.00 = 32A which matches the 32A ring requirement ---- single 6491X "Singles" 4.0mm is thus ok
So I stand by my suggestion of Option 1.2 in 4.0mm 6491X for the 32A ring feed, with 1.5mm 6491X for lighting feed.
The conduit 6491X run is still fed by twin FTE-2.5mm & single FTE-1.5mm from the CU (ring+light) and leaves by twin FTE-2.5mm & single FTE-1.5mm at the loft end.
www.gil-lec.co.uk for 6491X 4.0mm Ring, 1.5mm Lighting. Sorry, I had steel conduit with 6491B singles on the brain.
--
DB.



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Dorothy Bradbury wrote:

All my cables run in a (wood) cavity wall. BCO never turned a hair.
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