Electrical cable outside

[Nobody]

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

[Dave Plowman (News)]

Yes - but SWA is the cheaper option material cost wise - and quicker to install.

[John Rumm]

Yes... or plastic

No, but you could use that without additional protection.

[The Medway Handyman]

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?

[John]

'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

[John Rumm]

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

[Nobody]

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.

[Harry Bloomfield]

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?

[Dorothy Bradbury]

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

1. 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

[John Rumm]

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.

"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:

[John Rumm]

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.

[Nobody]

[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.

[Dorothy Bradbury]

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.

for 6491X 4.0mm Ring, 1.5mm Lighting. Sorry, I had steel conduit with 6491B singles on the brain.

[Dorothy Bradbury]

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.

[John]

>>> 'Fraid I have to take exception to that article John. If the conduit is

that's better mate,

cheers,

John

[The Natural Philosopher]

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

[Dave H.]

Just took a look in the TLC guide[1] to the 16th ed' and it looks like it's derating if buried in insulation (50% of free-air current capacity), and caution re leaching of plasticisers etc. along with cautions re damp bridging (although wall ties certainly touch both leaves of the cavity?) - I have a through-the-cavity 16sq.mm feed to the "loft CU" myself, but that's in what was the external cavity (uninsulated) before the house was extended and is now a double-leaf internal wall... Whether it complies or not is a mystery to me, as it was put in long before Prat P came into force - I have replaced the old cable like for like with new "harmonised" due to slight mechanical damage, as permitted under part P ;o)

-- Dave H. (The engineer formerly known as Homeless)

"Rules are for the obedience of fools, and the guidance of wise men" - Douglas Bader

[1]

[Dorothy Bradbury]

I think the limitation on cables in a cavity wall is thus... o Some people used to drill at two points thro the inner leaf o At the top drop a plumbob o At the bottom feed in a metal loop so it expands left & right o Thus feed cables through brick cavities

In this instance cables are potentially... o Unsupported over a large vertical run o Against metal brick ties, risk of unseen damage during fitting o In unknown positions re adventurous CWI drillers etc o Subject to future additional insulation requiring derating o Difficult to replace and "left to cook" if insulation added o Routed without regard to min bend radius inside leaf

Of course one can argue the cable is >2" from the surface thus need no protection & need not run vertically etc etc.

Part P of course requires you to use the same route as old, no mention of the route requiring adherence to BS7671. That may be a factor in IEE "going all RCBO" re zones.

I suspect many houses do run cables down the brick cavity, especially for loft & showers - too tempting vs alternatives.

I agree re risk of obsession about fixed vs appliance wiring. Local "co-op" has perfect hierarchical sized trunking/conduit, beautifully arranged singles, cables, everything throughout. It would make a BT linesman weep at obsessive precision. Every fridge has sheath 4"+ short of BS4343 cord grip, bare singles holding a 3m cable drop, one with CPC out. Each one with green PAT label attached. I suspect partly caused by walking on cords - so pulling on ceiling plugs.

All our cables ran thro a cavity, impossible to get to re built-in tanks above, chimney below & to side, absolutely no consideration for ambient derating. Every single cable has the copper conductor black with cupric oxide, insulation will not slide off the conductor. Insulation must be physically scrapped off tiny bit by bit with a knife - the copper shaves more easily. Replacements take a distinctly cooler (& BS7671) route.

Local brick-outer-leaf, shed-inner-leaf apartments ran cables (white so LSOH) thro holes in the wood inner leaf. Others ran cables thro metal studding without protection so that will be an interesting problem in years to come re vibration. LSOH cable sheath has as much abrasion resistance as cheese.

[<me9]

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.

[Dorothy Bradbury]

Wall ties are designed to drain from inner to outer leaf. Unless your brickie fitted them the wrong way around, whereupon they will train from the outer to inner leaf.

Same route & size, perfect compliance under Part P :-) Slight mechanical damage is... so useful.

Elec Factors odds are on earth rods for PME installations re risk of broken neutral. I suspect they just have a shed full :-)

Talking of cavities... I prefer burying gov't officials face down, so you always have somewhere to park the bike if you see what I mean.