Building a deck this week, complicated bugger but that's not important.
Going around the existing patio (and the new deck) is a power supply to the adjacent shed. Its a 2.5mm TO&I cable encased in white PVC flexible conduit - a bit like the stuff used to tidy up cables behind your PC.
Current owners moved in 3 years ago & it was already there, not mentioned on survey. Next door seem to have the same thing, nobody is sure how old it is.
Is this legal & safe? Nothing to do with me really, the deck doesn't go near it, just seems a bit of a bodge. I thought you had to use armoured cable?
Should I advise the householder to get it checked out?
No offence, but you ain't qualified to offer an expert opinion other than you have your doubts and, perhaps, it don't look right to you. All you can do is advise the householder to seek the advice of an electrician. Whether he does so or not is up to him, but it's then out of your hands.
Well the main risks with T&E outside is exposure to sunlight and lack of mechanical protection. The fact that it is sleeved in something helps greatly. However it is impossible to say how good or bad it is without knowing what the arrangements are made at both the head of the cable, and what is going on in the shed.
John Rumm coughed up some electrons that declared:
I've just cut off and made safe a bit of T+E dangling between the trees, feeding some gate lights.
I would estimate it to be about 10-15 years old. It wasn't brittle but the sheath was noticably harder than it should have been. Don't know how much longer it would be before it became dangerously hardend, but it was well on its way.
The PVC round conduit on the last leg to the bulkhead fittings shattered when I touched it with the strimmer cord (hence the urgency in disconnecting the circuit) - that was very very brittle.
So yes, sunlight does very much affect PVC, from first hand experience.
Loads of sheds are supplied by T&E. It may not meet new install rules but its standard equipment and works ok, and is normal for existing installs. You've got conduit too, luxury. No reason to get it checked
Loads of sheds are supplied by T&E. It may not meet new install rules but its standard equipment and works ok, and is normal for existing installs. You've got conduit too, luxury. No reason to get it checked
I've known a number of lengths of PVC T&E exposed to sunlight, some of them older than me and dating back almost to the introduction of PVC wiring. None have deteriorated noticably (unlike me).
There are numerous makers of PVC cable, and they are not all then same even when new. Some are much softer to strip and cut than others for example. Most of them are affected by sunlight in some way, but to what extent varies. Very few will harden so much as to become brittle enough to shed insulation all by themselves, however after prolonged exposure, they may become more succeptable to damage when hit or bent. Some will basically remain as they were when new and just get a bit stiffer.
The main problem with T&E outside is it is not strong enough to bury directly, and is not that well suited to hanging from a support wire. Running it in conduit (even plastic) is fine in many cases. It will usually be ok clipped to a wall on its own.
What you need to watch is that inappropriate use of it is not also an indication of a lashup in other respects - like inadequate earth fault protection, or exporting a house earth in inappropriate circumstance.
The most likely one would be a house with a TN-C-S (PME) earth - i.e. one that is derived from the suppliers neutral conductor at the main cutout in the house. One of the potential faults with these installations that needs to be given consideration is what happens if the suppliers neutral were ever disconnected but the live left unaffected (JCB through cable etc). This would leave the neutral and the earth floating. Given it would be connected to the live side of the supply via all your appliances, and there would be no current flowing, so the potential of the neutral and earth (and by implication the metal cases of all your appliances) would tend to rise to 240V.
This obviously raises a possible serious shock risk. There are a number of things than can be done to mitigate the effects of the problem. One of these[1] is good equipotential bonding - making sure that an equipotential zone exists in the house that electrically commons together anything that might acquire a different electrical potential from the electrical earth/neutral. This has two effects - the fortuitous earthing of things like water and gas supplies will tend to lower the touch voltage experienced anyway, and more importantly, if you are unable to make contact with conductive parts that are at significantly different voltages, its hard to get a shock in the first place - even if the things you are touching are all at 240V. The Faraday cage principle.
Now maintaining an equipotential zone is easy enough inside a nice insulated house. However if you want to feed power and the PME earth to an outbuilding, you need to also ensure the equipotential zone is maintained in it as well. So for example if the building had a tap connected via a metal pipe, that would need a main equipotential bond. This then has the knock on implication that the earth you supply to the building needs to be large enough to function as a main bonding conductor as well as an earth (so 10mm^2 copper equivalent as a minimum). T&E on its own does not have a suitably sized CPC (earth wire) to perform this function. The real problem comes with buildings where there is easy access to an independent earth i.e. something with a bare soil floor like a greenhouse. Here it is virtually impossible to make the exported PME earth safe, since you can't control what other potentials it is possible to make contact with along with the earth. The solution in these cases is to use the PME earth only for protecting the submain to the outbuilding but then to isolate it on entry so that it is unused and inaccessible in the building. You then provide your own earth connection locally using an earth rod. This makes the outbuilding TT install[2] in its own right, with its own RCD protection.
[1] Needless to say the supplier will also try to mitigate the dangers of this fault condition by ensuring they connect their combined neutral and earth conductor to real earth at a number of separate locations.
More on the subtleties of taking power to outbuildings etc cxan be found here:
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.