Exporting Pme 2016-09-21

[marcuswareham]

Its about time PME issues like this were addressed with safety monitoring devices that cut the supply at the origin should a loss of neutral occur.

Argee

 

[LastManOnline]

As already said, you can extend the PME to the outbuilding if you BOND any extraneous conductive parts adequately.

For the vast majority of sheds, if there is an extraneous part it's likely to be the waterpipe. I would be inclined to insert a section of plastic pipe and convert it to "un-extraneous" (is that English?). Less hassle at times, than running out a 10mm earth.

 

[i=p/u]

Metal walls, metal roof , grill floor , all bonded

 

[old man sparky]

Metal walls, metal roof , grill floor , all bonded

Car parked next to shed bond it, metal gate bond it, lady walking by with a pram bond it. rubbish me steel toe caps !! bond it ??

 

[LastManOnline]

Its a very poor situation IMHO when we are now looking at the 18th edition of BS7671 with all the regulations contained there in. And we still have a possible situation where the whole lot can become live to the touch, bypass every protective device in the install, and the only way its addressed is to fit oversized bonding and hope the potential victim is wearing thick soled shoes. Its about time PME issues like this were addressed with safety monitoring devices that cut the supply at the origin should a loss of neutral occur.
In the meantime I will stick with my thoughts that extending TNC-S to a wooden outbuilding is fine, TT my preferred option, but I will never use both methods together. Just my preference. Wonder if the 19th edition will come up with something else to fit into your TNC-S compliant, Non combustible, SPD and RCBO filled C/U. its gonna get crowded in there. ?

A figurative red warning flag has been waving over the dangers of the TNC-S supply system for some time now. You do wonder if it will take a high profile incident (hopefully not) to raise awareness to a point where definate steps must follow. That was literally what happened to cause the introduction of rcd,s into mainstream electrical installation work.

 

[old man sparky]

A figurative red warning flag has been waving over the dangers of the TNC-S supply system for some time now. You do wonder if it will take a high profile incident (hopefully not) to raise awareness to a point where definate steps must follow. That was literally what happened to cause the introduction of rcd,s into mainstream electrical installation work.

Manufacturers of EV charging stations are already on the case ?

 

[mattg4321]

Got an interesting one come up on an EICR today.

TN-C-S earthing system for property. Detached garage run in 2.5, 3 core SWA 'exporting. Theres a metal water pipe pops up out of the ground about 200mm inside the garage from the standard up and over door. Just has an 'outside' tap on the end of the pipe. Measured 3k ohms between pipe and MET. No bonding to pipe.

How do I code that? If the pipe/tap was 300mm away outside the garage I wouldn't even have given it a second thought. IMO an equipotential zone isn't practical to achieve in a garage with a concrete floor and up and over door. Bonding it (even were the SWA to be 10mm) doesn't seem to make it any safer to me. You're already standing on true earth, and 200mm away is outside the garage anyway.

Clearly the safest option would be TT for the garage, but that's not really required by the regs or we would have that stipulation for all garages/outside sockets/garden lights etc etc

 

[westward10]

Earthed Equipotential Zone hasn't been used by BS7671 for years.
Nor do you "export" PME you are merely utilizing a cpc derived from a PME source.

 

[old man sparky]

The garage supply is nothing more than a glorified extension lead or submain radial supply if you like. Connecting back to the mains position, and its the mains position that's the origin of the supply, and that's where your PME is. Your extending the earthing arrangement yes but not exporting the pme. As far as coding I wouldn't. If that's worthy of a code then our nice new metalclad boards are all C2s if PENs lost.

 

[westward10]

The garage supply is nothing more than a glorified extension lead or submain radial supply if you like. Connecting back to the mains position, and its the mains position that's the origin of the supply, and that's where your PME is. Your extending the earthing arrangement yes but not exporting the pme. As far as coding I wouldn't. If that's worthy of a code then our nice new metalclad boards are all C2s if PENs lost.

How can you Code the loss of a PEN connection when no mention of this is made in BS7671. I really don't get people's obsession with PEN losses.

 

[MDJ]

I'm glad someone thinks so ?

well one person at least ?

 

[old man sparky]

How can you Code the loss of a PEN connection when no mention of this is made in BS7671. I really don't get people's obsession with PE

How can you Code the loss of a PEN connection when no mention of this is made in BS7671. I really don't get people's obsession with PEN losses.

Agree coding is a non starter as said (I wouldn't) You cant start coding based on what may happen if PEN is lost. The C2 scenario was just by example of where and how far do you go, and where do you stop. Although why are there now increased sizes in main earthing and bonding conductors where TNC-S is used , maybe there is something in BS7671, maybe in time it will go further. There are a lot of regulations in the 18th that didn't exist in the 14th per say. So just because its not in there doesn't mean it won't be there in future editions. There is a potential danger with a lost PEN. If you were on the receiving end of a 230 volt live conductive part I think you would probably be a little concerned.
And I think the discussion on this thread comes from a place of concern rather than obsession. EV charge stations are rapidly on the increase, and with PME being most DNO's adopted earthing preference, you are going to see something addressing issues and short comings with the system, be it by way of amendment's or in a future 19th edition, who knows ? WE have RCDs we have RCBO's we have SPD's and soon we may have the edition of lost PEN monitoring devices on TNC-S systems, who knows. We all have our opinions after all, and its great to discuss different view points ??

 

[Simon47]

How can you Code the loss of a PEN connection when no mention of this is made in BS7671. I really don't get people's obsession with PEN losses.

Because a) it happens, and b) when it does, then the suppliers "earth" terminal is now "live" at anything up to 240V depending on loads on the system.
Within the house there isn't a massive problem as stuff is bonded to form an equipotential zone and so even if all your "earthed" metalwork is at (say) 150V, there's no touchable sources of true earth to cause a shock - like working in a Faraday cage.
Once you go outside then it's different - hence why the restrictions on charging EVs now.

EDIT: Removed the load of stuff that belonged in a different thread

 

[newfutile]

I think this why be why the proposed amendment 2 includes earthing house foundations , this will be another PME earth make a more complete faraday cage, until a cat or dog walk outside .