External T&E Cable Mechanical/UV Protection

[Careful_Bodger]

For existing external cable drops in 1.5mm T&E, say to security lights, is there a retrofit capping I can fit?

A link or part number would be most useful.

I appreciate (from previous posts on this forum) that PVC T&E should not be used externally, but given that it has, is there anything I can usefully do that doesn't involve ripping it all out and replacing with Arctic/SWA?

TIA

 

[SwindonSpark]

Careful_Bodger, any form of capping would only provide mechanical protection but your main problem is temperature.

The PVC twin & earth cable becomes brittle at 0 degrees C.
Since yours is used externally (naughty naughty!) it will be subject to cold temperatures at night. Especially during the Winter.

Well you might argue that it doesn't move much, but did you know that cable is subjected to mechanical stress caused by carrying current?

Look at this picture: -

Magnetic fields are created around the conductors.

Now you have two conductors in your PVC twin & earth carrying current in opposite directions: -

The two conductors will repel each other and this magnetic field is created 50 times a second causing 50 repulsions per second.

At very cold temperatures (below 0 degrees C), your PVC twin & earth will become brittle any any movement will cause degredation and the insulation may break down.

Once the insulation breaks down (and remember that this is installed externally), then water WILL manage to get into the cable and it's only a matter of time before it fails.

That's why ARCTIC cable was created. It stays pliable upto -20 degrees C.

Capping is not the answer. Replacing with Arctic cable is. Unless you only intend to use the security lights in Summer!

This is the stuff: -

http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=62948&id=63305

 

[securespark]

Swindon - your arguement does not hold up entirely. PVC is allowable outside - what is most SWA, after all? Furthermore, I can see no reason why pvc cannot be used outside if protected by black conduit - black is uv resistant and the main problem with pvc outside is not temperature but the effect of UV on the cable.

 

[SwindonSpark]

Agreed that black conduit is UV resistant and it is a good idea for Careful_Bodger to install it since he's already used PVC twin & earth.

However I'm aware that others read these threads to get ideas and tips. There may be some who are considering using PVC twin & earth externally and I'm pointing out the problems.

 

[securespark]

So, without wanting to sound aggresive (a la J Paxman), pvc as a material can be used on cables used outdoors then?

 

[plugwash]

arctic cable is PVC

there are many trypes of PVC designed for different environments. There are two problems with PVC outside.

one problem is the combination of cold (to the point at which the plasticisers stop being effective and the material becomes brittle) and movement (i personally doubt that stresses from magnatism are significant) and also the effect of UV (which for some reason effects black PVC far less than other colours possiblly because it cant penatrate very far into the material).

I think UV is by far the bigger of the two issues though.

 

[mapj1]

A couple of points,

Further to Swindon spark, the magnetic force will indeed rise and fall, but 100 times a second, HOWEVER, the force is piddling
http://theory.uwinnipeg.ca/physics/mag/node10.html

The force for 1A , and a 2mm spacing between L and N (and really its more spacing, so less force than this) is 0.000019 newtons per metre length. There are 100grams per Newton, so we can say the force is equivalent to
0.0019 grams for every metre of length. This is if the current is 1A (240 watts) otherwise it scales. The forces due to the earths magnetic field are higher. For significant Electromagnetic repulsions, you need 1000s of amps, millimetres apart, possible during a short circuit, but not for long before something melts.

(to 'unzip' Twin and earth you need the best part of a kilogram force per centimetre of length !)

I think we can neglect magnetic forces in this. The enemy is sunlight depleteing the plasticiser over time.

regards M.

PS.
I have assumed
u=4 x 10- 7 T m/A,
pi=3.14

and Force=u*I1*I2/(2*pi*d)
I1=-I2

all close enough for estimation purposes

 

[ban-all-sheds]

Last year I took down some white T/E which had been an overhead supply to a garage for at least 17 years.

It was fine - the outside of the sheath had become rough and dirty, but there was no sign of any gross mechanical deterioration. I have a feeling I still have it somewhere, just because I never got round to chucking it out - if I do I'll run an insulation test on it and let you know what I find.

 

[securespark]

I never got round to chucking it out.

So, the dreadful truth is finally revealed: You Are A Dreadful Hoarder.

 

[Careful_Bodger]

Thanks for the help everyone.

I was hoping that there would be something like

that I could use. Would look okay. Minimum Fuss. Can see something like it on overhead cable drops on street supplies.

Spooky Paxman impersonation, by the way SecureS.

Brave try Swindon - but I do know a bit about Electromagnetic Theory (only 20-odd years as an RF engineer....groan).

Cheers All.

 

[ban-all-sheds]

So, the dreadful truth is finally revealed: You Are A Dreadful Hoarder.

I am, but in this case I'm not hoarding the cable in case it comes in handy*, it really is a case that I just haven't got round to chucking it out. I disconnected it as we were having the pebble-dashing redone, and were also dismantling the patio roof to which it was attached. As the plan is to get rid of the garage and replace it with a wooden garden office, I never bothered to reconnect it - I don't use the garage for anything except storage, so no power is at times a nuisance, but no more.

It's still coiled up under the stairs where I left it .

*mind you, if the insulation resistance checks out OK.....

 

[SwindonSpark]

Careful_Bodger wrote:
Brave try Swindon

Ah well, yer tries yer best!

 

[securespark]

I'm now feeling sorry for Swindon as it seems he's been ganged up on.....

 

[Lectrician]

The table in the res shows T+E is suitable for outside use. Movement at cold temperatures is not issue if the cable in clipped. It may be best to avoid all day direct sun light, and the regs to state this. They also state not to install PVC at low temperatures, due to the reasonds mentioned.

There is nothing prohibiting the use of pvc T+E outdoors.