Exporting Pme 2016-09-21

[marcuswareham]

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 the voltage between PME earth and the electrode is >50v , although I guess there is a risk of N current and fault current going down said electrode if things went wrong so would probably need 10mm bonding, doh ?


Can 722.411.41 (iv) be applied to a metal outbuilding using a PME earth also, so using a voltage sensing relay and a contactor to break L, N & PE if the voltage is outside of 207v - 253v, to lower the risks (although doesn't make them go away), I know 722.411.41 is for EV but but could the same idea be used in this case

 

[LastManOnline]

It might not be 230v, could be more or less depending on phase balance, Perhaps we need to contact all our neighbours on our local transformer and get everyone to use there oven, tv and electric shower, etc all at the same time of day so the phases stay balanced, then no voltage on CPC in a PEN fault , hahahaha ?

Correct. There are so many variables involved in determining what voltage will eventually be present under open PEN that I usually just assume worst case scenario (for purposes of discussion)

 

[LastManOnline]

Can 722.411.41 (iv) be applied to a metal outbuilding using a PME earth also, so using a voltage sensing relay and a contactor to break L, N & PE if the voltage is outside of 207v - 253v, to lower the risks (although doesn't make them go away), I know 722.411.41 is for EV but but could the same idea be used in this case

Can't see any reason why not. You still feel though that the sulutions we are currently endeavouring to supply for TNC-S issues are not ideal. Reality is TNC-S as a "supply system" is not ideal.

 

[marcuswareham]

Can't see any reason why not. You still feel though that the sulutions we are currently endeavouring to supply for TNC-S issues are not ideal. Reality is TNC-S as a "supply system" is not ideal.

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)

Shame we dont have access to all 3 phases in houses, its quite easy to detect a PEN fault with 3 phase

 

[Msitekkie]

Just realised this thread was about 5 years old.

Mmm, but quite relevant at the moment, with so many home offices going in

But you haven't read GN8. Surely this would be a good starting point?

Maybe.I probably will get a copy eventually. Unfortunately I can't afford a full set of Guidance

But you haven't read GN8. Surely this would be a good starting point?

Maybe. Unfortunately I cannot afford a full set of Guidance Notes at the shocking price they are available & I am still working through Sparky Ninja's online webinars, which are more accessible & certainly cheaper... Some good stuff on earthing.
I probably will get GN8 eventually, but probably by the time I have finished Sparky Ninja's resources a new edition will be out.
What I am really interested in regarding earthing & I suspect not covered by GN8, is how to go about fitting an earthing mat when I have my drive done that will help me in future to use my Solar power off-grid ("Islanding"). I gather from Sparky that proposed standards talk about earthing mats for new builds, e.g adding them to foundations, but no guidance on retro-fitting.

 

[old man sparky]

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.

 

[LastManOnline]

Mmm, but quite relevant at the moment, with so many home offices going in

Maybe.I probably will get a copy eventually. Unfortunately I can't afford a full set of Guidance

Maybe. Unfortunately I cannot afford a full set of Guidance Notes at the shocking price they are available & I am still working through Sparky Ninja's online webinars, which are more accessible & certainly cheaper... Some good stuff on earthing.
I probably will get GN8 eventually, but probably by the time I have finished Sparky Ninja's resources a new edition will be out.
What I am really interested in regarding earthing & I suspect not covered by GN8, is how to go about fitting an earthing mat when I have my drive done that will help me in future to use my Solar power off-grid ("Islanding"). I gather from Sparky that proposed standards talk about earthing mats for new builds, e.g adding them to foundations, but no guidance on retro-fitting.

This whole area of installing (or retro fitting) earth mats/rods etc is surprisingly not as well discussed as it could be. There are options out there that could be explored like the kilometers of disconnected metallic services in urban areas already in situ that could be "reactivated" for earthing purposes

 

[LastManOnline]

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.

Your point highlights nicely the variables that come in to play during an open PEN FAULT.

Every buggers supply load see's yer poor old Rod as a brightly shining light is seen by moths.

Are you referring here to the standard earth rod?

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.

Agreed. The construction of the shed is a major fact in the degree
of potential danger under open PEN fault

 

[old man sparky]

Never used a twig for TT if thats to be known as a standard rod. Hate the bloomin things. So always a substantial rod which of course adds to the reasoning regarding keeping the two earthing arrangements separate. The brighter the light the more moths you attract. Thing is there may well be parallel earth paths upstream but with water and gas arrangements turning to pvc I still reckon the rods going to be a favourite. As said use one or The other but not both. Each system will do the job if installed properly.

 

[LastManOnline]

Never used a twig for TT if thats to be known as a standard rod. Hate the bloomin things.

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

So always a substantial rod which of course adds to the reasoning regarding keeping the two earthing arrangements separate. The brighter the light the more moths you attract.

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

Thing is there may well be parallel earth paths upstream but with water and gas arrangements turning to pvc I still reckon the rods going to be a favourite. As said use one or The other but not both. Each system will do the job if installed properly.

Same question as above?

 

[old man sparky]

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. ?

 

[mattg4321]

You could have the same problem though with a metallic service pipe that’s bonded back to the MET.

 

[old man sparky]

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. ?

 

[Msitekkie]

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.

 

[newfutile]

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