Twin and earth outside

[RF Lighting]

I've been asked to look at an EICR of a privately owned old peoples home carried out by another contractor.

One of the items that has been flagged as an issue are some external lights. They are wired in twin and earth cable clipped to the external stonework of the building, and they are saying the lights need to be rewired.

Whilst I know it is not an ideal situation, I can't see it as really being a problem, and am looking for some actual evidence such as regulations which might support the argument either way.

 

[ericmark]

Standard: BS6004 Electric cables. PVC insulated, nonarmoured cables for voltages up to and including 450/750V, for electric power, lighting and internal wiring

To me that says internal but "and" does not seem right word from Batt Cables Website.

 

[EFLImpudence]

Applications: domestic wiring and lighting systems

Not much better.
The education system is not what it used to was.

 

[mfarrow]

BS 6004 says "the presence of water in contact with the cable is not acceptable". Other than that there's not a lot in the 2012 version about it.

Earlier versions are a bit clearer and do state unsuitable for outdoor use.

 

[ban-all-sheds]

Whilst I know it is not an ideal situation, I can't see it as really being a problem, and am looking for some actual evidence such as regulations which might support the argument either way.

Presumably you'll refuse to recognise 134.1.1

 

[JohnW2]

Whilst I know it is not an ideal situation, I can't see it as really being a problem, and am looking for some actual evidence such as regulations which might support the argument either way.

Presumably you'll refuse to recognise 134.1.1

I imagine that everyone 'recognises' 134.1.1 but it is so vague and subjective that I don't see that it really helps RF with his question.

The reality is, of course, that I think we all know that unprotected T+E firmly attached to an outside wall, 'exposed to the elements' will usually last for decades without problems - so that's probably one of the things one would have to take into account when trying to decide whether this constituted a 'proper material' as required by 134.1.1.

Kind Regards, John

 

[mfarrow]

The oldest I've seen (in 2010) was installed in 1972 as part of an extension (to an outside light under undisturbed floorboards). The sheath was cracked but was OK underneath and the core insulation was just fine.

I suppose one needs to ask yourself as a designer, if choosing to use T&E outside of it's recommended working environment:

- How often will this installation be EICR'd (either industry recommendation or otherwise)?
- Given the variances in manufacture, location, climate etc, what is the probably maximum deterioration rate of this cable?
- Given the above, how certain can I be that cable deterioration will be picked up by the EICR interval?
- What should the interval before the first EICR be on the EIC given the possible deterioration level I've determined by answering the above?

I'm not sure I could fully answer any of those, but if I used a cable whose standard does not lead me to have to answer them, then I'd be a lot happier.

 

[JohnW2]

The oldest I've seen (in 2010) was installed in 1972 as part of an extension (to an outside light under undisturbed floorboards). The sheath was cracked but was OK underneath and the core insulation was just fine.

Very similar experience here. Two or three years ago I removed a long run of grey T&E from the outside wall of my house. I'm not sure of the age, but some indication is given by the fact that it was imperial cable - so probably at least as old as yours. The cable was fine. Not even any major cracks in the sheath, the core insulation looked fine (where I inspected it) and it IRd 'as good as new'.

I suppose one needs to ask yourself as a designer, if choosing to use T&E outside of it's recommended working environment:
- How often will this installation be EICR'd (either industry recommendation or otherwise)?
- Given the variances in manufacture, location, climate etc, what is the probably maximum deterioration rate of this cable?
- Given the above, how certain can I be that cable deterioration will be picked up by the EICR interval?

Possibly - but, certainly for a domestic installation, I think you might have to make the 'worst case' assumption that it might never be EICR'd. However, since we all seem to believe that (special circumstances aside) it would probably last for at least 'a few decades', then I'm not sure that there is any reason to be concerned (in common sense terms - considerations of regs, employers, insurers, scheme operators etc. may be a different thing!). There are very few other products we would buy and 'use' which we would expect to have a fault-free life that long!

Kind Regards, John

 

[EFLImpudence]

Is it the plasticisers which lead to this (supposed?) degradation?

There are many products (without plasticisers) manufactured from PVC intended for use outside - doors, windows, gutters, fascias, pipes etc.

Could it be said that any T+E which does show signs of degradation in a relatively short time was not made very well?

 

[JohnW2]

Could it be said that any T+E which does show signs of degradation in a relatively short time was not made very well?

It could certainly be said. Frankly, I haven't personally come across a case of, or personally heard of a case of, PVC T+E which did "degrade in a relatively short time", so I have no idea whether such a phenomenon is any more than a 'rarity'.

Kind Regards, John

 

[bernardgreen]

Could it be said that any T+E which does show signs of degradation in a relatively short time was not made
very well?

Yes

When the three runs of PVC twin and earth along my neighbour's stone wall were removed after about 30 years some was still "flexible" and some was extremely stiff and the sheath cracked easily. It was all installed about the same time so there had to be a variation in the quality of the cable. ( as regards to tolerance of the external environment )

 

[westie101]

Given that when PVC was first introduced it was given a nominal life (based on guesswork I think) of about 25 years. Is it not the case that the recomendations are possibly still based on that initial advice.

Whilst it appears that results vary I somehow doubt any proper experimentation has been done into it's life in a number of different conditions

 

[bernardgreen]

I somehow doubt any proper experimentation has been done into it's life in a number of different conditions

Some work was done on predicting life expectancy of various cable materials for cables feeding antenna at the top of tall masts. I don't have the results. I do now recall that the cables feeding the lights were not "standard" twin and earth. ( aircraft warning lights )

 

[ericmark]

I assume RF Lighting does not want the cable and wants to show it's non complaint and as it if it could be used or not is not the issue it's down to some rule saying don't use it.

Product Description

Manufactured to BS 6004:2012 Table 4

Plain Annealed Copper Conductor / PVC Insulated / PVC Sheathed with bare
Circuit Protective Conductor. 300/500V.

Designed for use in light industrial and domestic wiring. These cables are particularly suited for installation as meter tails and are intended for fixed installation in dry or damp premises

These cables can be instaled in conduit, in cable trunking and in cable ducting. Or where there is deemed little risk of mechanical damage there cables can be clipped direct, on cable try, embedded or in free air. These cables are not intended to be laid underground.

It says "in" premises so I would read that as also meaning not outside the premises.

 

[JohnW2]

I assume RF Lighting does not want the cable and wants to show it's non complaint and as it if it could be used or not is not the issue it's down to some rule saying don't use it.

I actually read RF to be being much more open-minded than that and, in fact, personally feeling that the cable was 'probably OK'.

It says "in" premises so I would read that as also meaning not outside the premises.

As I understand it, the main potential issue is the effect of UV light, and I can think of a good few situations I've seen in which exposed T&E 'inside a premises' has been exposed to a lot of UV, in some cases probably as much as it would be exposed to if 'outside'.

Kind Regards, John