Exporting Pme

Exporting Pme 2016-09-21

No permission to download

Discuss Exporting Pme in the Electrician Resources and Downloads area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

So do I. Am obliged over here (ROI) to install them with every new install and rewire (our supply system is TNC-S). Always terrified of hitting underground pipes/services

Do I conclude from this that you feel your earth rod can be a potential danger under open PEN?

Same question as above?
I feel if you dont combine TNC-S with TT you dont need to consider the scenarios of what can potentially happen if an open PEN situation ever developed. A floating voltage suddenly has a return path with unknown currents introduced and limited by the resistance of maybe just the rod maybe not. Why would you allow for that scenario to happen. I prefer not to, its just me. ?
 
You could have the same problem though with a metallic service pipe that’s bonded back to the MET.
If compliant the bonding would be suitably sized for TNC-S and back to the MET, this would also be within the equipotential bonding zone, so not the same issues.
With an out building using a TT system where a TN-C-S earthing has been extended beyond the bonding zone and effectively connected as a combined earth with the Rod. Your into a different scenario, if the PEN is lost downstream.
(Referring to the comments that have gone before on this thread).
So if your extending the PME then you install to that. If your going for TT then that's ok.
But choose one or the other not both. There's really no point.
When we did the installations for petrol stations back in my younger days. PME was not allowed.
TT or TN-S yes but not TN-C-S.
That's it !! off to bed, stay safe guys. ?
 
TT and PME joined happily together.
Broken PEN upstream of yer supply with Mrs Jones at number 42 having a shower and Mr Smith cooking the Sunday roast at 48. Every buggers supply load see's yer poor old Rod as a brightly shining light is seen by moths. Best keep em separate, Mind you if its a nice wooden floored shed with no bonding needs even the swa glanded properly will often be a good enough cpc for extending yer TN-C-S arrangement.
Thanks for sharing that thought provoking response.
 
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
 
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.
 
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. ?
 
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
 
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.
 
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.
 
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 ?
 
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
 
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.
 
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.
 

Reply to Exporting Pme in the Electrician Resources and Downloads area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock