Exporting PME to Socket in high street.

Tricky. It sounds like what gets plugged in aren't exactly caravans - so aren't necessarily legally banned from using PME Earths like real caravans (and boats) are by the ESQCR. These sockets sound more like "Highway power supplies" - so more likely fall under 714 - which doesn't have any blanket PME prohibition (at least in BS 7671 itself). I'm not familiar with the guidance you mention unfortunately.

As you say, constructing a TT system in a busy high street isn't simple of itself - not only the issue of other items within reach (lighting columns, street signs etc) being on PME, but positioning the TT electrode so it's sufficiently distant from any metalwork in the ground connected to PME (e.g. including the sheath/armour of buried cables and bonded metallic gas/water pipes) not to be influenced by any rise in potential on the PME system could well be "challenging".

I suspect the risks are typically lower than for a (worst case) caravan too - less bare soil and bare feet - shoes and tarmac can be reasonable insulators for example.

   - Andy.

Unless its a domestic caravan, its probably not all that similar. A supply that was real TN-S would be ideal of course but there is almost none of it left in some places.

Be aware that things like lamp-posts and bus stops and so on in built-up areas are quite commonly fed from PME /TNC-s these days, and while it pains me to say it, in practice they seem to give little trouble - so for example do the floor mounted lights have exposed metal that is on the PME earth ?

Also note that although the IET guide you refer to implies that connecting PME to a stall is illegal, 

That actually is not quite what the ESQCR says -rather we have

The words 'temporary' and "conductive material" do not appear at all in the actual legislation, only in guidance, - so there is no legal prohibition on the use of PME in temporary structures. It may not be a good idea however ;-) and the advice of the guidance is correctly to point that out.

The problem is , that I fear that  if you wanted to change to TT, you'd have to change everything else in the street as well,  to get far enough away.

Have you spoken to the makers or tried to get the original installation data ? There may for example be a grid electrode that is connected to the PME earth - which is about the only way you can use PME in a wet environment and be sure what the ground is doing.

You don't really want to dig things up to see how it was done if possible to avoid that.
Mike.

M.

It is a publication from The IET, chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/electrical.theiet.org/.../guide-to-highway-electrical-street-furniture.pdf  Cheers for the reply

I did send a eamil and they have no data on the project, I can not see a earth electrode, something I did look for on the installation.If you read section 6.3 Section considered Are all one with resitriction with PME! They do not have skill person on hand market day Nor test the Items.So if they can not satifiy anyone of those its a fail. Cheers for the reply

The high steet has work done by local council and highways. Highways do the main lighting infrastructure and local council do feeder pillar boxes for market traders and events (events cover a lot of diffrent things as you can imagine). Regards the bus shelter note you mentioned section 7.1 of the guidance note says TT.

One of other reason I have gone to fail it the plug a burger van in too! but they will just tell them to run off a Geny. Not sure there is proper control of what gets plugged in. Flop flops in rain and precived shock also pops in my mind. It carrys on. 

And there, in the lack of oversight is the problem - it is essentially uncontrolled, and in reality  clearly even a PME socket will be far safer than the alternative of a petrol genset and jerrry can sitting totally unearthed behind the burger grill, whatever the guidance suggests,

Note that while by law a DNO cannot connect a supply and mains cut out and so on into a boat or a caravan - that does not mean a consumer can't plug one in on an extension lead into their house installation or whatever, and of course plenty do - but the risk is the same, they are just blissfully unaware of it. It is also why EV charging and earthing have become such a hot potato with lost earth detectors and so on.

note that of all the DNOs western Power are the most upbeat about this see this excerpt fro their guidance suggesting its OK if there is main bonding in place at the origin.

In reality of course reputable campsites and marinas do have TT earthed feed pillars, but not all the smaller ones by any means.

Equally I'm not sure that most bus stop installers round here have ever read that guidance, and by the sound of it neither do the street sockets team in the OP's area !

Which raises a rather interesting question - if no-one is watching the shop, as it were, who has asked you to test this lot and what powers do they have to change things if you were to recommend it should be rewired ?

Mike.

M.L.R said:

So I have failed/or going to fail the installation due to exporting the PME to the socket outlets and for others reasons.

Would Section 711 be more relevant, Regulation 711.411.4, than Section 708 ?

It's National Grid now not Western Power and I've found them to be slightly less upbeat now than in the WP days.
WP were always one of the most efficient/ contractor friendly DNOs to work with

apologies it has indeed changed name - to one certain to cause confusion but ho-hum - luckily it still looks like that document is still their  latest thinking, despite the change of name. More generally the pragmatic contacts DNO-side are very folk much worth cultivating ;-)
Mike.

It does feel like TT'ing the sockets etc. in this situation is likely to be somewhere between difficult, impractical and impossible. Just too much PME influence around (both below ground and within reach above ground). To cover most bases you'd probably have to look at something like a buried grid extending under the whole area that could potentially be served by the sockets (and even that approach tends to raise issues at the extremities unless you have more than the usual amount of space to play with).

I can't help thinking that the least worst solution in this kind of case would be to use the PME earth but with the addition of an open-PEN device - if you have 3-phase available the 3-phase versions (that reference against an artificial N point) don't have the blind spots that the single phase types are notorious for. Not a directly documented BS 7671 arrangement admittedly, but BS 7671 does allow for novel approaches provided they provide a solution that no less safe than direct BS 7671 compliance.

   - Andy.