Open PEN solution

[LastManOnline]

How many threads have there not been regarding the issues resulting from employing a TNC-S supply system? The current earthing arrangements to mitigate the consequences of a broken DNO neutral are not satisfactory and are not likely to change in the foreseeable future largely due to cost. But has EV charging not provided a reasonably priced solution?. Why not employ open PEN sensors for the entire domestic installation should a DNO Neutral fail??

 

[Spoon]

But has EV charging not provided a reasonably priced solution?

The Zappi EV charger V2 detects a broken PEN conductor, and does a lot more.
Looks like a really nice EV charger.

 

[pc1966]

It seems like a great idea...but...disconnecting the earth from the whole installation worries me. Sure if you only have the mains power coming in then it should be safe, but with folks having PV systems and occasionally UPS or backup generation it would make me a bit uneasy.

Disconnecting just the line conductor on a out-of-range supply as some of the "open PEN" boxes do (Matt:E and similar) would save your home from excess volts, and I guess if all on the same failed-PEN section did that you would not need the earth/CPC to be disconnected.

Now if we only had some box in series with the line, with a cutout and some smart electronics...

 

[pc1966]

Disconnecting just the line conductor on a out-of-range supply as some of the "open PEN" boxes do (Matt:E and similar)

Just to clarify what I just said - the Matt:E box and similar disconnects all 3/5 conductors (L, N & E or L1-L3,N & E) to protect against open-PEN volts. What I meant was the same disconnection test using out-of-range voltage.

 

[marcuswareham]

I like the idea as I still struggle as to why we live with this risk of open PEN conductors, yes we mitigate by doing PME and inside an equipotential zone you will probably be ok (although people who have received a shock standing on an "insulated wooded floorboard might disagree). Yes why not make it so this fault cannot occur on the network (running a separate earth conductor seems the smartest option for me (true TN-S)) but once again cost is reducing safety (and I guess that all those PME earth electrodes cost less than the extra conductor). Also if PME was a satisfactory solution why would we be having all the fuss with EV charging, Well because it is outside the house, but so are hot tubs, swimming pools, outside lights, deck heaters, bonded outside taps etc. not much new about using electricity outside (I have plastic double insulated outside lights for the exact reason of a PEN fault, as my outside light are very easy to touch.

The Zappi EV charger V2 detects a broken PEN conductor, and does a lot more.
Looks like a really nice EV charger.

There are a few EV charges with "detect" an open PEN conductor the problem is they dont!, The Matte single-phase device disconnects L N and CPC if the voltage is outside of a range, although this offers some protection it is very possible to still have a dangerous situation and the voltage remain within the allowable range due to phase imbalances and extraneous conductive parts (matte themselves even demonstrate this in one of there videos)

The Zappi does not detect an open PEN it does the same as above but with the addition of detecting if someone is receiving an electric shock because of a PEN fault, much like a class one device supplied from an RCD without a CPC, if you get a shock from it the RCD should disconnect but it requires you to receive a shock thats why we have the CPC to enable it to be ADS. That is exactly how the zappi is working it requires a person to receive a shock to disconnect so it is NOT ADS (watch their video where the guy simulates touching a car using a banana lead I wonder why he didn't use his hand !!!), it is better than nothing but not really a solution.

The best solution I have seen is the Matte 3 phase device which has 3 resistors configured in a star configuration between phases, this provides a "virtual" natural point so the difference between this point and the PEN conductor is measured and then disconnection occurs if the difference is above 70v. This device also has ensures all phases are present as a phase loss would stop the device from working properly. This option works well it will not detect a open PEN if the phases are balanced but then there is not a risk of the PEN being a dangerous voltage, This type of device I guess could be implemented on the electrical grid, but not for domestic properties as most houses only have 1 phase

I have been working on another solution, which is not perfect but an idea. Basically a device which does a Ze loop impedance test every 200ms, and if the loop impedance is above the allowable 0.35ohm for TN-C-S is will disconnect L N and CPC, this can detect a PEN fault because if the PEN goes open the Ze will normally rise unless you have exceptional extraneous conductive parts (under 0.35ohm) in which case there is no risk of high voltage on PEN, If the 3 phases are balanced the device should still work as the current will be returning by the other phases so the loop impedance test will be measuring the impedance though the connected loads on the other phases which will hopefully be more than 0.35ohm. So I think this method should be able to monitor for PEN faults on a single-phase installation

 

[pc1966]

There are a few EV charges with "detect" an open PEN conductor the problem is they dont!, The Matte single-phase device disconnects L N and CPC if the voltage is outside of a range, although this offers some protection it is very possible to still have a dangerous situation and the voltage remain within the allowable range due to phase imbalances and extraneous conductive parts (matte themselves even demonstrate this in one of there videos)

Agreed there.

The Zappi does not detect an open PEN it does the same as above but with the addition of detecting if someone is receiving an electric shock because of a PEN fault, much like a class one device supplied from an RCD without a CPC

Which is also a very good point.

However, there are ones that detect the high PEN voltage but they need an earth rod, and that is often not a feasible option in areas of concrete & tarmac & buried services. Also they seem to bitch about high rod impedance so you might need 2 * 1.2m rods, etc.

I have wondered if they really need a low-R rod, as they should be able to disconnect on the fault voltage and not on the resulting earth current as a traditional TT system is going to do. In that case you could almost have some wire and conductive paint on concrete, or a small rod in soil, and still be able to detect the risk.

 

[LastManOnline]

Yes why not make it so this fault cannot occur on the network (running a separate earth conductor seems the smartest option for me (true TN-S)) but once again cost is reducing safety (and I guess that all those PME earth electrodes cost less t

Agreed. A separate earth was always the way to go.I would imagine the decision to abandon TN-S is going to cause ongoing headaches for a while. And just one high profile electrical incident resulting from an open PEN will put it right back into the headlines again. Most countries responded to the loss of TN-S or the loss of a low impedence TT system (utilising the metallic services as a fault return path) , by turning to TNC-S. Cost savings obviously were very attractive. But not all. One European country went "full" TT, by sinking an earth rod that with an RA lower than an ohm. How smart that decision looks in hindsight

 

[pc1966]

To a large degree the open PEN risk is something that was not so critical until recently when outdoor hot tubs and EV resulted in wet people having the option to complete the circuit, and most service pipes are now plastic and no longer offer a nice low Ra bond in most homes.

But we are here now. Not there. So we have to look to ways to get out of this in a manageable way.

In the UK there is talk of 18th amendment 2 requiring low R earths in new houses, which is fairly easy/cheap to do at the time. I know ROI has a requirement for an earth rod in addition to the supply PEN, though how much it helps in practice is not something I have read about. Certainly the aggregation of lots of rods would help, even if the odd one does not.

A lot of the EU is TT, which obviously avoids this but means reliance on RCD for primary protection and putting in rods, which in many built up areas is difficult and hazardous due to unmapped buried services.

 

[LastManOnline]

I know ROI has a requirement for an earth rod in addition to the supply PEN, though how much it helps in practice is not something I have read about.

Difficult to determine how much it helps in practice. Of course it will be of some help in reducing touch voltage. Main problem is, we really can't determine HOW MUCH help. We can't measure the effectiveness of the DNO, s earth rods or indeed the neighbours. So that situation is not ideal.
Second issue that you correctly alluded to, is getting the rod into the ground in an urban area in the first place. It can be a terrifying experience. And if you do hit something you will have a major problem on your hands. Last year I had the "pleasure" of dealing with my public liability insurer for the first time since I became self employed (26 years). It was memorable for all the wrong reasons

 

[Mike Johnson]

A lot of the EU is TT, which obviously avoids this but means reliance on RCD for primary protection and putting in rods, which in many built up areas is difficult and hazardous due to unmapped buried services.

There is a legal requirement on all statutory suppliers to provide locations of any buried service (EU57 applies) even the London Hydraulic company have drawings showing the runs of their pressure pipes in and around London, however their main souse of income is from other suppliers compromising their supplies and they being the only persons allowed to repair same, I still have some shares somewhere although the dividend per year is minimal, bit like my Costain shares ? the value of which is so low I can't understand why they have not been raided.

 

[pc1966]

Having plans availalble helps (we used one of those services to check where the local 11kV cable went and for any gas/water recently before driving in rods), but you can be sure there will be drawing errors and undocumented stuff as well.

 

[marcuswareham]

And there is the risk of your electrodes being to close to other PME electrodes or buried services in the ground and then PEN fault appearing on your electrode, but i guess if it was done at the point the foundations where done and to every house on an estate its almost like making a very large out door equipotential zone ?

 

[Spoon]

we used one of those services to check where the local 11kV cable went and for any gas/water recently before driving in rods)

Out of curiosity, how mush does something like that cost?

 

[pc1966]

Out of curiosity, how mush does something like that cost?

It was free:

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