temporary supply for marquee

[Paul_C]

Breaking Live and Neutral will not remove the hazard that the PME "earth" wire is at a voltage high rnough above ground to create a hazard to anyone touching the ground and the "protective" "earth".

If the potential on network neutral has risen above ground to a hazardous voltage then the "earth" has also to be disconnected as is is as dangerous as the neutral from which it is derived.

My tongue was slightly in my cheek, as obviously the contacts would have to open the incoming neutral ahead of point at which the installation's earth is bonded to it to remove the hazardous potential, as you say. In the U.K, that would mean on the supplier's side of things, obviously.

Personally, I would always install my own earth electrode with PME anyway as an extra safeguard. In other parts of the world, such local electrodes at each service entrance are required.

 

[JohnW2]

My tongue was slightly in my cheek, as obviously the contacts would have to open the incoming neutral ahead of point at which the installation's earth is bonded to it to remove the hazardous potential, as you say. In the U.K, that would mean on the supplier's side of things, obviously.

Well, you wouldn't actually have to interfere with "the supplier's side of things" if you used a 3-pole device to disconnect L, N & E (i.e.disconnecting the link between DNO's 'earth' and the installation's MET) - but that would be a definie no-no in terms of UK regs!

Personally, I would always install my own earth electrode with PME anyway as an extra safeguard. In other parts of the world, such local electrodes at each service entrance are required.

Same here - although the relatively high impedance of the electrode's path to earth would obviously mean that it would be of fairly limited value.

Having said that, I do wonder whether we don't perhaps get a bit over-excited about the potential hazard of a lost PEN on a TN-C-S system. For a start, it's undoubtedly very rare. Secondly, it's not going to be an 'un-noticed' fault, since the installation won't function (with your added local earth electrode, it might try - but wouldn't get very far!). Thirdly, unless one co-incidentally is unwisely exporting the earth to a marquee (or whatever) at the very time of the fault, if one has a well-engineered equipotential zone within the premises, there ought to be minimal risk. Nevertheless, I'm quite happy that I don't have TN-C-S!

Kind Regards, John.

 

[Buzx1313]

i really do not see the problem here,, if you have a supply to a tent or what ever protected by rcds then what is the problem?

I do hope you're not one of the poor souls who are misguided into thinking that RCDs are the be all and end all of electrical safety....?

no i am not .. far far from it,, see further up the posts..

i am just practical, i get frustrated by contractors being so anal about things..

at the end of the day we export pme all the time to sheds gararges, out buildings, outside sockets, outside lights, shall i go on.. and there are very few problems ..

all iam saying if aunty flo is putting up a marque for a bit of a bash i see no problems in running a pme supply to it.. If it was a steel building and it was very wet and everyone wsa running around naked then its a different matter..

there are certain people on here quick to critisise other peoples thoughts and ideas and make it personal,, also assuming that they have little or no knowledge of electricity and how it works..

these are the same people that will do a periodic report and fail it because there are no RCDs on the sockets, this does not make a socket unsafe to use..

just being pracital