Twin & Earth Outdoors - how to protect it?

[JohnW2]

Yes T&E is not really suitable officially but in practice it is and often suffers less than expected and is ok for years

Indeed.

When my parents bought their house in 2009 I found an extension lead (H05VV-F) strung along the fence to power a garden room, possibly since 1989. It was still in great condition so I pulled it from the fence and kept using it.

"Strung along the fence" might not last as long as 'firmly clipped to a wall'. The main 'risk' when PVC cable is exposed to UV is that it may become brittle and therefore at risk of splitting if bent or otherwise 'disturbed'. That's unlikely to happen if it is firmly clipped to a wall', but may be more likely if it is 'strung to a fence' (depending on how that 'stringing' has been done, and how rigid/immobile the fence is!).

 

[Ragnar_AT]

As I said, even loosely draped (I can’t remember any details but the lead exited an old attached brick shed under the eaves, was somehow held up along the top of a timber gate but not attached to the gate itself and then ran along a brick boundary wall, mostly held in place by ivy) the flex was in great condition.

 

[Jurassicspark]

As I said, even loosely draped (I can’t remember any details but the lead exited an old attached brick shed under the eaves, was somehow held up along the top of a timber gate but not attached to the gate itself and then ran along a brick boundary wall, mostly held in place by ivy) the flex was in great condition.

Did you IR test the cable?

 

[JohnW2]

Did you IR test the cable?

Good question, particularly given that the OP describes a cable which was somewhat 'flapping around in the breeze', hence any PVC which had become brittle might well crack.

However, it's worth pointing out that IR can be misleading, giving 'a false sense of confidence'. This was due to a rodent, but similar might possibly happen due to PVC becoming brittle and cracking when disturbed, but it IRd just fine ....

 

[IfInDoubtDIY]

Ok so yesterday I started fitting the security light - I took down the old one (and the junction box was full of water!) and when I went to remove the cable I discovered that it actually DOESN’T come out of the soffit at the top! It comes out at the BOTTOM of the roof and had just been pushed up inside the soffit. Anyway, I cut everything away and mounted the new light (routing the cable through a hole in the wall). As for the Twin and Earth, it was fine where it had been under the soffit but where it had been exposed to the elements was quite badly damaged.

 

[Ragnar_AT]

I didn‘t see any reason to do an IR test since the outer sheath was in such perfect condition but might test next time I get there out of sheer curiosity. Can’t be terrible because it didn‘t trip a recently tested 30 mA RCD but still interesting to know the actual IR value.

 

[JohnW2]

I didn‘t see any reason to do an IR test since the outer sheath was in such perfect condition but might test next time I get there out of sheer curiosity.

As I've said (and illustrated), IR testing does not necessarily prove much, particularly if the cable is installed in a matter which precludes it being significantly 'disturbed'

Can’t be terrible because it didn‘t trip a recently tested 30 mA RCD but still interesting to know the actual IR value.

There is obviously a very very big difference between the impedance/resistance of an L-E fault which would be great enough to trip a 30 mA RCD and an IR measurement that would be considered 'unsatisfactory' - roughly the difference between about 7,667 Ω and 1,000,000 Ω. The absence of RCD trips therefore doesn't tell one much is relation to IR, other than that the L-E IR must be above about 8 kΩ !

 

[Ragnar_AT]

As I said, I pulled the extension lead off the fence 15 years ago and have been using it for various tasks around the house ever since.
I‘m definitely aware of the fact that an IR of, say, 100 kOhm would be very much unsatisfactory but still far from tripping a 30 mA RCD. That’s why I wrote „terrible“.

 

[JohnW2]

As I said, I pulled the extension lead off the fence 15 years ago and have been using it for various tasks around the house ever since.
I‘m definitely aware of the fact that an IR of, say, 100 kOhm would be very much unsatisfactory but still far from tripping a 30 mA RCD. That’s why I wrote „terrible“.

Fair enough - but my point obviously was that if it had an IR low enough to trip an RCD (i.e. <7.67 kΩ), it would be 'seriously terrible', to say the least

In fact, other than in cases in which there is mechanical damage to the insulation to the point of conductors actually touching (hence IR close to zero), I don't think I've ever seen a PVC cable with an IR less than at least 'a few hundred kΩ) - have you?

 

[Ragnar_AT]

Nope, even a 1920s motor that spent pretty much the last 60-odd years sitting unused in a basement along with original VIR cables came in at 150k.