Outside lights

[Stephen]

Hello,

Please could you tell me what is the correct way for a [part P] person to cable to an external light?

The tidiest way is probably to run cable under the first floor floorboards but this can be a nuisance to do, so if the cable is run along the exterior of the house, should the twin and earth be run in conduit or just clipped to the wall?

One person has told me that if clipped to the wall, the plastic will degrade in UV light, so I was thinking conduit was the answer. However a second person has told me T&E will "sweat" in conduit, whatever that means. Who is right?

Thanks.

[Tim S]

Stephen coughed up some electrons that declared:

That can happen. There are other types of UV resistant cable - one called "HiTuf" would be very suitable. Nothing special to terminate, it's basically a very tough flex.

so I was thinking conduit was the answer. However

Rubbish.

Cables are rated to carry lower currents in conduit, compared to being "clipped direct" to a surface, and clipped direct is lower than on ventilated cable basket or ladders.

For most lighting circuit arrangements (6A or 10A MCB), you'll be fine with

1.0 or 1.5mm2 in conduit.

From the OnSite Guide:

1.5mm2: In conduit on a wall = 16.5A Clipped direct = 19.5A Conduit in thermally insulating wall (ref method A) = 14A On perforated cable tray = 22A

In the same order, for 1.0mm2: 13A, 15A, 11A, 17A

A bit of black conduit can look quite smart on a wall - just put a bit in to carry the main earth bond to the gas meter.

Cheers

Tim

[Dave Plowman (News)]

Personally I think TW&E run externally looks cheap. Best option is bare MI cable which is small and neat and will blend in well with most stone or brick. Otherwise HiTuf.

[Andrew Gabriel]

That is often quoted as a theoretical possibility. However, I've never seen it happen, even with PVC which has spent decades in the sun. You could paint the cable if you want, which would provide even more UV protection, and blend it in better with the wall. Slip some paper behind it to protect the wall, and then paint with oil based gloss topcoat directly, without any undercoat. Slide the paper out whilst the paint is still wet, so it doesn't stick.

Possibly referring to considerations of condensation formation and drainage in conduit?

[John Rumm]

What is a part P person?

In conduit is better generally since it give mechanical protection as well.

It does degrade *slowly* in UV, but the actual amount will vary on the amount of exposure and the particular cable used. Something sheltered would probably last indefinitely. The main risk would be something in full sun that is also prone to getting knocked. The T&E insulation may get brittle with exposure and age.

HITuf is ok, but it is quite bulky for a given size, and as easy to handle as bagpipes! (its very stiff, and the outer insulation takes some stripping!)

No it won't. As Andy says you may get some condensation though (which basically means drilling the occasional drain hole in fittings)

[Andrew Gabriel]

Should use plastic sheathed MI if the wall contains cement, to prevent any reaction with the copper sheath (only necessary outdoors).

Unfortunately, the plastic sheath on MI doesn't seem to be protected against UV, and generally flakes and drops off.

[Dave Plowman (News)]

Doesn't seem to be a problem in practice - I've got some over 30 years old which is showing no corrosion. Just a nice patina.

Oh dear. ;-)

[Stephen]

Thanks for all the replies. What do you put at the end of the conduit, and should you finish the T&E in the conduit and run a short length of flex into the light, since in theory the light can be moved through an angle?

[John Rumm]

Depends on the light. Some will have a mounting box with 20mm knockout. With these it is easy to terminate the conduit directly onto the box. With others a flex outlet may be required.

[Tim S]

Stephen coughed up some electrons that declared:

If it's hanging downwards, you can use nothing (lets condensation out which is a plus).

Or, use one of these:

welded on

and one of these:

a tight seal (or the round equivalent for flex)

If you want to transfer to flex from T+E, you could put a besa box or similar upstream

put a terminal strip in (assuming it is accessible to check the terminals in future) or use crimps or solder and some heatshrink.

I wouldn't stuff crimps up a conduit without a box though - people really wouldn't expect that.

Obviously ensure you fit a gasket to the besa box lid for outside use :)

HTH

Tim

[js.b1]

Part P non-notifiable is...

- cable enters light from rear, no external connections (new light fitting)

- cable enters however if light fitting pre-existing (cable replacement)

Bollocks really. I prefer to plug lights into a Masterseal socket. A bit ugly I'll grant you, but your mind will soon change when you can prewire a light fitting (and its replacement) sat on the ground then walk up a ladder, fit it to the wall & plug in. A lot better than trying to fiddle with an upside down junction box, whilst balancing on a ladder, which is usually metal, some 20ft up in the air.

No-one is going to plug a hedge trimmer into it and the supply can be (S)FCU protected at 3A as necessary on the inside. You can not however use this with more complicated 4-wire PIR lights. Don't think Masterseal do a "T-earth" pin version.

If it is a PIR, they tend to last longer when sheltered under eaves.

Surprised no-one suggested the obvious cable...

- White 1.0mm NoBurn cable from TLC

- UV ok, outside ok, just adhere to 6x min bend radius

The red is not UV proof and tends to oxidise a bit pink over time.

DP Sw or FCU on the inside? FTE from wherever into it, through rear via 20mm conduit spanning any cavity, into 20mm galvanised BESA box on outside with 6491X earth fed back through conduit to isolator, exit bottom of galvanised BESA box via IP68 gland to drip-loop into light. Most lights are IPx4, or claim to be whilst havin a larf, so do not forget the drip loop into the light fitting.

If you did use FTE with any gland it needs to be a Pratley gland - they are listed on TLCs website.

[Tim S]

js.b1 coughed up some electrons that declared:

3 phase "red" commando? One earth, one neutral and 3 live pins to play with :)

[js.b1]

Exactly... what... SIZE of light were you planning :-) Close Encounters Of The Lumen Kind...

[Tim S]

js.b1 coughed up some electrons that declared:

Ha!

The 16A isn't that big...

Now, with the 125A you could have some fun - perhaps a set of flootball ground floodlights instead of a normal halogen PIR?

Burglars, hawkers and unwanted visiting relatives would simply be vapourised - kills the weeds on your drive too.