Exporting Pme 2016-09-21

[LastManOnline]

Would it not be better and easier to install a pen fault device as they do for EV?
like a Garo G6EV40PME Consumer Unit, MCU Type A RCBO & PME Fault, EV Charger Compatible

I think so, especially if its the type that does, nt require installing a rod

 

[i=p/u]

I believe its suppliers problem

 

[Simon47]

Instead of making a metal outbuilding TT and having a high impedance electrode and then relying on RCDs and having the possibility of 2 earthing systems in close proximity, could you use an earth electrode (for measurement only) and a voltage monitoring relay that opens a contactor (L, N & PE) if ...

Except, and CBA looking up the numbers, the regs prohibit switching the earth. Or they did until the latest edition which ...

Indeed yes I do feel like it is an incomplete solution, but better than nothing especially if the item in question is unlikely to be touched etc (unlike an EV)

allows switching of the earth, and in fact requires it, for EVs

As already said, you can extend the PME to the outbuilding if you BOND any extraneous conductive parts adequately. That mean min 10mm2 of copper, or more if calculations say so. If the bonding is inadequate in cross section, then under fault conditions it'll melt.

Yes, teh same argument apply within the main dwelling - which is why we have main, and if required supplementary, bonding to create an equipotential zone.

 

[old man sparky]

Except, and CBA looking up the numbers, the regs prohibit switching the earth. Or they did until the latest edition which ...

allows switching of the earth, and in fact requires it, for EVs

As already said, you can extend the PME to the outbuilding if you BOND any extraneous conductive parts adequately. That mean min 10mm2 of copper, or more if calculations say so. If the bonding is inadequate in cross section, then under fault conditions it'll melt.

Yes, teh same argument apply within the main dwelling - which is why we have main, and if required supplementary, bonding to create an equipotential zone.

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. ?

 

[marcuswareham]

Except, and CBA looking up the numbers, the regs prohibit switching the earth. Or they did until the latest edition which ...

allows switching of the earth, and in fact requires it, for EVs

As already said, you can extend the PME to the outbuilding if you BOND any extraneous conductive parts adequately. That mean min 10mm2 of copper, or more if calculations say so. If the bonding is inadequate in cross section, then under fault conditions it'll melt.

Yes, teh same argument apply within the main dwelling - which is why we have main, and if required supplementary, bonding to create an equipotential zone.

So is switching of the earth prohibited, but only allowed for EV charging?, and therefore if you used a device (matt-e, garo etc etc) to protect against a PEN fault by switching the earth but not for an EV but instead for an outbuilding or hot tub or similar would that be prohibited as the only mention of switching the earth is in EV charging section?, seem a bit of a gray area

I understand the reasons why the bonding of a metal shed needs to be a min of 10mm.

Although in bonding a metal constructed shed this would bring the whole shed up in potential in a PEN fault condition so you might be protected inside the shed as if everything extraneous is bonded then everything should be at the same potential inside the shed, But what about the guy leaning against said shed standing on some wet grass with no shoes on ?, or maybe more realistic: opening the metal shed door with a metal handle whilst outside and in contact with true earth

 

[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.