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Topic Title: EV charger earthing
Topic Summary: Use of VOELCB where earth impedance is high
Created On: 14 March 2019 11:09 AM
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 14 March 2019 11:09 AM
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26tannahill

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Joined: 14 March 2019

I recently had an ev charger installed in my pme protected house. My house is built on sandstone rock therefore getting a TT earth is very difficult. Since the change to 18th edition there is no easy solution. Looking at the issues led me to believe the VOELCB which was installed in the house I grew up in was the answer. On looking at Geoff Cronshaw's article I discovered the regs had got there before me and the 450 ohm loop impedance of a single rod could solve the problem if I put in a VOELCB to monitor the voltage to earth of the PME connection, all I need now is a VOELCB.

Does anyone know of a supplier supplying one which meets current standards? A search on the internet does not suggest there are suitable suppliers.

I am concerned seeing the costs of obtaining an earth in my conditions that this may become a serious problem if installers do not accept the cost risk or VOELCBs are not incorporated in charge points. I am interested to know if others have experienced this problem?
 14 March 2019 11:39 AM
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mapj1

Posts: 12039
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As far as I know the all pole disconnecting earth sensing device of the regs is as yet a thing of the imagination only.
I agree, if private EVs are to ever catch on for ordinary folk, then this sort of thing will need to be adressed properly.
Though, if you can get 450 ohms with one rod, then two spaced a rod length or more apart and wired in parallel gets you into the sort of territory where RCD based TT looks quite sensible. Or a connection to re-bar in the garage floor or wherever a large area concrete slab meets terra firma, or the use of shallow horizontal electrodes.

-------------------------
regards Mike
 14 March 2019 03:59 PM
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26tannahill

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Thanks for interesting response. The situation is that the house is only about 60m from the substation. The substation is built on similar ground and I suspect has a relatively high earth impedance, limiting the effectiveness of further rods. The installer eventually put 5 in the ground and got down to 120 ohms. Luckily I agreed a fixed price and they were true to their word.

I have been noticing that some public charge points do not work with some cars and yet do with others. I suspect earth loop impedance is the issue. Advice I have received suggests that EVs measure earth loop impedance before charging, so just getting it down to enough for the RCD is probably not enough. Given that most home EV charging installations have used the "impractical" get out in the 17th edition and connected to the PME terminal, this issue is relatively new. I suspect the fact that it has so widely been assumed that PME was adequate has led to the change in section 722.

I am a retired engineer with little experience of the regs. So I enjoy looking at these issues theoretically, so practical advice is gratefully received. While I do not theoretically now need a solution, I would like to not rely on the vast quantity of copper now put in the ground with a rock drill. I can see it failing if we have a long dry summer. Also I am keen on seeing EV vehicles more widely adopted, this is not going to help.
 15 March 2019 10:18 AM
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AJJewsbury

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The substation is built on similar ground and I suspect has a relatively high earth impedance,

I think the DNO aren't allowed to have their electrode resistance exceed 20 Ohms - so you should be OK on that score.

There are some EVSE manufacturers who seem to claim they have charge points that are safe to use on PME - seemingly they disconnect all poles including PE from the car should PME earthing be lost (broken CNE) - but how they do this seems questionable since they don't appear to need a local earth electrode to provide a reference 0V.

Of course there is a simple (if not cheap) solution to all this - for the DNOs to give up on all this PME nonsense and go back to a proper TN-S distribution system.

- Andy.
 15 March 2019 12:29 PM
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ebee

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"Of course there is a simple (if not cheap) solution to all this - for the DNOs to give up on all this PME nonsense and go back to a proper TN-S distribution system."

The voice of reason!

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 18 March 2019 01:25 AM
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MHRestorations

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TN-C-S to me is fundamentally unsafe, if they ever do it to our installation, i'm going to TT it
 18 March 2019 06:05 AM
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gkenyon

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Originally posted by: MHRestorations

TN-C-S to me is fundamentally unsafe, if they ever do it to our installation, i'm going to TT it
Do you have TN-S at the moment?

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 18 March 2019 01:20 PM
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ectophile

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Originally posted by: MHRestorations

TN-C-S to me is fundamentally unsafe, if they ever do it to our installation, i'm going to TT it


Is TT safe? Unless you've got a steel framed building, you are unlikely to get an earth rod resistance low enough to blow the supply fuse, or even trip an MCB on a final circuit.

So you are then relying on an RCD to trip in the event of a fault. If that RCD goes sticky, it may fail to trip, leaving the installation live.

TN-S also has problems. Nobody monitors the resistance of the earth. So on an old supply, which may be decades old, the earth could go high resistance, and nobody would notice until it was too late.

-------------------------
S P Barker BSc PhD IEng MIET
 19 March 2019 12:27 PM
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AJJewsbury

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TN-S also has problems. Nobody monitors the resistance of the earth. So on an old supply, which may be decades old, the earth could go high resistance, and nobody would notice until it was too late.

Here's an idea - building in earth monitoring into the new smart meters. Once a problem is detected it can 'phone home to the DNO to get the problem fixed (and if it affects several properties all the meters would call in, allowing the DNO to better guess the location of the fault before they even turn up). The meters could even monitor voltage levels - to detect broken N etc - and even disconnect the supply to the consumer if they reach dangerous levels - probably a cost saving for the supply industry there if it saves on payouts for burned out consumer appliances.

- Andy.
 19 March 2019 02:17 PM
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gkenyon

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Andy, that would be great, and it has been looked at ... at least in other countries.

The problem is, in the UK, the DNO isn't the Meter Operator, and it could well the the case that neither are your electricity supplier.

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 19 March 2019 06:39 PM
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chrispearson

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Originally posted by: ectophile

TN-S also has problems. Nobody monitors the resistance of the earth. So on an old supply, which may be decades old, the earth could go high resistance, and nobody would notice until it was too late.


Well, your wise homeowner will have had his EICRs done ten yearly; and after any alterations or additions, any competent electrician will have noted an elevated Zdb in the course of writing up a MEIWC. So there is plenty of opportunity to identify a dodgy TN-S earth.
 19 March 2019 09:47 PM
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Legh

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Andy,
You appear to be totally in favour of smart meters, almost a lobbyist! You argue the case convincingly. I think that if SMETS 2 or maybe SMETS 3 could provide that level of protection you are advocating then I think I might agree with you, but until then the meter companies can continue to provide estimates or/and send round a meter reader from time to time..

Legh

-------------------------

http://www.leghrichardson.co.uk

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 19 March 2019 10:53 PM
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KFH

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Sorry Andy, your proposal would add a few pence to each meter and would remove the opportunity for everyone on the supply side to make more money, sorry that should have read: better meet our customers needs, in the future as did the suggestion to incorporate isolators in the meter.
 20 March 2019 09:07 AM
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AJJewsbury

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The problem is, in the UK, the DNO isn't the Meter Operator, and it could well the the case that neither are your electricity supplier.

But don't SMETS 2 (and later) meters communicate with a common central location, regardless of who the electricity supplier is? From there it should be relatively easy to pass on a message to the appropriate DNO regardless of the ownership of individual boxes.

I guess my view is that supply side problems should be dealt with by the supply industry rather than the consumer. The equipment needed to protect against such problems would typically require some means of measuring voltage, some logic, a means of disconnecting the supply and ideally a means of communicating with the supply industry - all of which are already present in smart meters - so it seems like an 'obvious' solution to me (even if it might require an additional voltage sensor and PE connection for some of the functions).

For sure there are security challenges with any smart system - but I'd be far more worried about a smart phone than a smart meter. At least the meter won't be able to listen to every word you utter (whether making a call or not), be privilege to every bit of data you send or receive, nor keep track of your exact position on the globe.

- Andy.
 20 March 2019 10:24 AM
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Zoomup

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For sure there are security challenges with any smart system - but I'd be far more worried about a smart phone than a smart meter. At least the meter won't be able to listen to every word you utter


Are we really sure of that Andy?

O.K. Google, can my electricity meter hear what I'm saying, and pass it on, and is your microphone switched on as well?

Z.
 20 March 2019 10:30 AM
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mapj1

Posts: 12039
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Still you can probably track the movement of the SMETS 2 meter if it moves around, as some designs use a standard phone chipset inside, that includes all the (utterly un-needed) location stuff. Of course, very few meters in basements and cupboards will get a good enough "view" of the sky to be able to see any sattelites.

Flipany asside any meter meeting the SMETS 2 spec
can
5.4.11.1 Average RMS voltage
ESME shall be capable of calculating the average value of RMS voltage over a configurable period as defined in the Average RMS voltage Measurement Period(5.6.3.5) and:
i. recording the value calculated (including the UTC date and time at the end of the period to which the value relates) in the Average RMS Voltage Profile Data Log(5.6.4.8);

which is really the L-N voltage.
So it is sort of in there.

-------------------------
regards Mike
 20 March 2019 10:47 AM
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ebee

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Big brother is volt-ing you!

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 20 March 2019 10:48 AM
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alancapon

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. . . But don't SMETS 2 (and later) meters communicate with a common central location, regardless of who the electricity supplier is? From there it should be relatively easy to pass on a message to the appropriate DNO regardless of the ownership of individual boxes. . .


Technically the answer is yes, excepting that the isolating contractor only isolates the phase(s) and leaves the neutral solid. However, in the UK, the idea falls fowl of privacy laws and data protection laws, in particular GDPR.

Regards,

Alan.
 20 March 2019 11:03 AM
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AJJewsbury

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excepting that the isolating contractor only isolates the phase(s) and leaves the neutral solid.

Even on a PME system with a broken CNE, switching off all loads (possibly excepting small loads with their own supplementary electrodes - e.g. street lighting) is probably sufficient to keep the severed CNE at a safe voltage; as well as perhaps protecting most appliances from overvoltages (e.g. 400V on a 230V system).

However, in the UK, the idea falls fowl of privacy laws and data protection laws, in particular GDPR.

How so? Surely with appropriate justification & registration any data (personal or not) may be kept and communicated?

Are we really sure of that Andy?

O.K. Google, can my electricity meter hear what I'm saying, and pass it on, and is your microphone switched on as well?

Reasonably - but I was talking about the mic on your phone, not the meter.

- Andy.
 20 March 2019 11:42 AM
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alancapon

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I am sure that it could be sorted. The issue at the moment is that the GDPR regulations are very new, and the prospective fines very large. Whether the meter would be able to react in time, I don't know. What you really want to do is open a three phase device at the substation, as opening individual single phase loads may unbalance the system again, causing more appliances to fail.

Regards,

Alan.
IET » Wiring and the regulations » EV charger earthing

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