Running PME (TNCS) outdoors?

[TheFullHitSpark]

Alright guys, ime racking my brains and books trying to find out why my boss told me that you are not supposed to run PME outdoors to say out feeding a garage or a shed of some sort, i know about potential differences.... also i know some about special locations but i just cant understand why your not allowed PME, surely if the cable is protected by an RCD, the same as it would be if you was using an earth steak for TT what is the difference?? can someone elaberate on this for me please. if this is the case you would have to have an earth steak which would be a seperate means of earthing than provided from your source, but obvioulsly your (PME) earth would still have to provide protection for the cable feeding the (sub main).

Thinking outloud abit..



If someone could show me the light i would be mostly appreciative.




Cheers guys, also as you all probably know this forum is the dogs go-nads...

 

[beaver74]

out of coriousity where is it stated that pme must not be exported i've looked but cant find it

 

[ian.settle1]

are you even a spark beaver? you wouldnt be using the neutral as a means of earth feeding the sub, it would be a seperate conductor. You dont make any sense!

I think you should read below before asking any one if they are an electrician it is you that is incorrect.

Defintions from Regs

TN-S A system having seperate neutral and protective conductors throughout the system.

TN-C-S A system in which the neutral and protective functions are combined in a single conductor in part of the system.

TN-C A system in which the neutral and protective functions are combined throughout the system.

You will normally find on a TN-C-S system that the neutral and earth are combined upto your cut-out where they will then be seperated to give you a seperate neutral and earth.

 

[beaver74]

I think you should read below before asking any one if they are an electrician it is you that is incorrect.

Defintions from Regs

TN-S A system having seperate neutral and protective conductors throughout the system.

TN-C-S A system in which the neutral and protective functions are combined in a single conductor in part of the system.

TN-C A system in which the neutral and protective functions are combined throughout the system.

You will normally find on a TN-C-S system that the neutral and earth are combined upto your cut-out where they will then be seperated to give you a seperate neutral and earth.

i thank you for you vote of confidance ian.settle1

 

[dixon9]

This explains in clear terms:

The risks from a PME installation stem from the
possibility of a ruptured neutral in the supply to
the consumer’s premises. The break in the neutral
could occur anywhere in the supply, and could
affect just one house or several houses, depending
on the supply arrangements. This could cause the
neutral, and the mains earth which is bonded to it,
to rise above the ‘true’ earth potential. To avoid
the possibility of metalwork inside the house being
at a different potential from the mains earth
(which in this case is at neutral potential), the IEE
regulations state that all metalwork such as central
heating systems, water pipes, gas pipes etc should
be securely bonded to the neutral at the PME
bonding point near the consumer unit, as in Fig 1.
In the unlikely event of a ruptured supply neutral,
the current which would normally return via the
neutral will attempt to return by way of all the
other earthed conductors – including the RF earth​

to amateur radio equipment (Fig 2).

http://www.rsgb.org/emc/pdfs/leaflets/emc7protectivemultipleearthingmembers.pdf

Also, I understand that you need to consult with DNO anyway before exporting PME.

 

[super spark]

just answered a similar question, perhaps this will help,

Subcategory - 1. BS7671 - Voltimum UK - Electrical Installation Products and Contracting



Subcategory - 1. BS7671

*
Local supply authorities*appear to have different requirements when taking supplies externally to*garages/outbuildings.
Here in West Sussex we are*told that we should take a Phase and Neutral supply only to a detached building and then install a local earth rod for the**external supply.
Some time ago an article*appeared in "The IEE Wiring Matters" by John Ware.*This stated that even with a PME supply to the house it could be achieved without an earth rod. The article appeared in Autumn 2005 issue 16.
I would appreciate your fact and regulatory*based comments.


*
BS 7671, and indeed, the article you refer to, give the requirements for electrical installations generally. Should local conditions, or in this case, the electricity supplier, require that further measures should be taken, their advice should always be followed.**
30-03-2006



*Back


For further information please contact:
Company:
IEE
Address:
The Institution of Engineering and Technology
Savoy Place
London
WC2R 0BL
UK
Telephone:
+44 (0)20 7240 1871
Fax:

 

[bateman585]

read the 17th edition, nickname ( the bumper book of fun ) pme or tn-c-s supports neutral, connot run live connductor outside of building, best way is run phase & neutral, to garage,
and put earth stake in for protection, only to garage consumer unit though, bit like a builders supply realy, but thats the reg's
i could explain in detail, but would take a long time

 

[IQ Electrical]

read the 17th edition, nickname ( the bumper book of fun ) pme or tn-c-s supports neutral, connot run live connductor outside of building, best way is run phase & neutral, to garage,
and put earth stake in for protection, only to garage consumer unit though, bit like a builders supply realy, but thats the reg's
i could explain in detail, but would take a long time

Where is this regulation? It has obviously been omitted from my copy of BS7671:2008 with corrigendum.

 

[SimpleSimon]

The only one I can recall is a PME supply shall not be run INSIDE a domestic premises.

 

[IQ Electrical]

The only one I can recall is a PME supply shall not be run INSIDE a domestic premises.

That reg refers to PEN conductors and is not restricted to domestic installations.

The PEN conductor only goes as far as the service head where it is separated!

 

[Deleted member 9648]

1. Apart from some special locations as defined in section 7 of bs 7671 there are no regulations in bs 7671 preventing a TNCS (PME) supply being used to supply external equipment and outbuildings.
2. The DNO dont give a ---- about exporting TNCS supplies as long as it complies with Bs 7671.
3. The reason regulations on exporting PME earths or separating for external supplies which are not a special location cant be found in the BRB is because they are not in there.
END OF.

 

[IQ Electrical]

1. Apart from some special locations as defined in section 7 of bs 7671 there are no regulations in bs 7671 preventing a TNCS (PME) supply being used to supply external equipment and outbuildings.
2. The DNO dont give a ---- about exporting TNCS supplies as long as it complies with Bs 7671.
3. The reason regulations on exporting PME earths or separating for external supplies which are not a special location cant be found in the BRB is because they are not in there.
END OF.

Ah, a pleasure to read......

 

[SimpleSimon]

That reg refers to PEN conductors and is not restricted to domestic installations.

The PEN conductor only goes as far as the service head where it is separated!

Does a PEN conductor form part of a PME?

 

[gamblor6]

lol wirepuller you REALLY hate this subject dont you.

 

[Deleted member 9648]

lol wirepuller you REALLY hate this subject dont you.

Whatever gave you that idea.........

 

[IQ Electrical]

lol wirepuller you REALLY hate this subject dont you.

Not as much as me, people just manufacture 'reg's based on rumour and opinion, it's pretty basic stuff in the scheme of things!

Guys use these threads to assist in their studies etc. so let's not make up regulations!