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Discussion Starter #1
There's been much discussion about earth rods and potential (!) issues for the common PME supplied properties. It appears most of the new regs are aimed at them. I've read as much as I can find, but there's just not much about TT earth properties - of which ours is one. So if the knowledgeable out there would indulge me:
1. Are TT earth properties inherently safer or is there a list of other issues to be dealt with when installing a charger?
2. Our supply is single phase 100A but a 50A RCD installed on its own in a box next to the main meter, supplies a second (and third) Consumer Unit in outbuildings (where the charger will be fitted), The earth to the outbuildings is via cable from the main incoming Meter cupboard earth rod. Should there be further earth rods for the "external" consumer units? Even if not "required", would further earth rods improve our installation or make no difference?
3. If I get a charger fitted, I will need a smart charger like a Zappi because I'll need to protect the supply to our plant room (ground source heat pump etc) and I'll need to make sure the max draw is below 50A. Does the Zappi2 with its new protection improve our situation or make no difference?
Thanks
 

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Speak directly to Zappi's technical department for their own installation requirements for your setup.

Also, there are other brands available that can do load management

You might also want a proper discussion with your DNO, especially if you are rural and share a small transformer with just a few other users.
 

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Discussion Starter #3
Thanks Freddym. I did approach the DNO years ago with a view to getting a three phase supply but costs were prohibitive (£10k just for the transformer + all of the cabling/runs/labour etc). My overall impression was that they weren't very helpfuI or interested in a domestic customer. I'm pretty confident that we are the only property on our transformer - its on a pole at the edge of our land where the supply transitions from overhead cables from the supply to our neighbour about 400m away and ongoing underground across a road to a farm about a mile away.

I was looking for a bit more discussion of the relative merits or otherwise of TT installations and their considerations vs others, particularly in an EV charging context, if you or others have time.
 

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Have you actually spoken to your DNO about the EV installation?

I suspect that your transformer will be shared with the two neighbours you have described.

Regarding your proposed EVSE, install another TT earth point dedicated for the EVSE if it is going to installed and used outwith any equipotential zone..

I suspect that the 50A RCD supply to the outbuildings needs rethinking: possibly the supply to the remote buildings needs to be protected by a correctly sized MCB and a time delay type S RCD, then the outbuildings should have their own earthing arrangements, RCDs. This needs sorting out by an electrician who knows what he is doing.
 

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I can only say that when my Podpoint was fitted, the fitter realised that my house, like yours, was TT, fed from a transformer in the field opposite. As a result I did not need an earth spike and the installation was very easy.
 

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Discussion Starter #7
Have you actually spoken to your DNO about the EV installation?

This needs sorting out by an electrician who knows what he is doing.
No, not yet spoken to DNO about our EV. As I said our DNO didn't appear interested in speaking to a domestic customer when I last tried so not very tempted to go back unless I have to.

The electrics here have all been renewed and tested (twice) in our tenure (last 12 years) - three different electricians for various aspects at significant cost, so a shame if its now proven that they didn't know what they were doing. Hence trying to improve my own understanding so that I can ask more searching questions up front.

Thanks Carty/Gary useful tips.
 

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As a minimum, you are possibly going to end up with issues of lack of discrimination and RCD blinding because of what you describe as the 50A RCD to the outbuildings. This of course introduces some real hazards and potentially would mean that a 2020 installation would not meet 18th Edition regs.

What is the type of RCD installed for the 50A supply to your out buildings.
 

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No, not yet spoken to DNO about our EV. As I said our DNO didn't appear interested in speaking to a domestic customer when I last tried so not very tempted to go back unless I have to.

The electrics here have all been renewed and tested (twice) in our tenure (last 12 years) - three different electricians for various aspects at significant cost, so a shame if its now proven that they didn't know what they were doing. Hence trying to improve my own understanding so that I can ask more searching questions up front.

Thanks Carty/Gary useful tips.
The Zappi has to be the best way to go given your situation.
The house show in the video had similar load problems as yourself by the sounds of it.
The Zappi has patented load and pen protection that no other manufactures can copy.
Do I have a Zappi - NO.
I have a basic Rolec unit, but it does the job just fine.
But if I was in your situation, I would not hesitate.
A little more expensive, but not had to see why.
The quality and engineering that gone into this unit has to rank it at the top of the pile.
 

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The DNO does not have an option but to be interested. They legally have to assess an application.

I recently had to speak to SSE about a very similar installation, pole mounted transformer serving 3 properties.

In the end, all parties agreed that the EVSE would have it's own separate TT earth, full RCD discrimination, 6mA DC detection etc etc.

Each case on its own merits of course.
 

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Discussion Starter #11
What is the type of RCD installed for the 50A supply to your out buildings.
Good prompt. I've not looked in the box for years, so took the top off and was surprised - not what I remembered at all. Thinking back, I believe it was changed when the plant room was done as the guy wasn't happy with the original set up to the outbuildings (although that had not long been tested and approved by the people who put in the PV on the Barn roof.)

Anyway, this is what we have - a standard Circuit Breaker

The big SWA cable goes underground to the outbuilding.

Regarding your proposed EVSE, install another TT earth point dedicated for the EVSE if it is going to installed and used outwith any equipotential zone..
This interests me. Why a second rod for the EVSE alone? Why not have a second rod serving the 2nd (and/or 3rd) Consumer unit as well as the earth cable that links to them from the rod on by the incoming mains. My (muddled?) thinking is that more earth rods means a better earth and some redundancy. And I don't understand the benefits of the earths all being separate/independent.
 

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It all depends on the impedance of the existing earthing point, the bonding of the various extraneous conductive items ( eg a BEV), other earthed structures such as metal fences, and ultimately voltage potentials that could exist under different fault conditions.
 

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From memory an earth rod and clamp is something like a tenner form screwfix, so as long as it's not a huge expanse of concrete, no big deal to put one in.
 

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Maybe I missed something in the video I posted regarding the Zappi unit.
Please excuse me if I am incorrect here guys, but I though one of the major advantages of the Zappi was that it does not require any type of earth rod ?. :censored:
 

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Discussion Starter #15
Yeah, you're right Carty, that's how they sell it. But in my case obviously I have an earth rod system anyway so I'm less clear if their clever work around will work in my scenario. As Freddym says, I'll probably have to ask them directly - happy to do that although always slightly wary of asking a supplier if their offering would be any good, the incentives for them to give a rounded view are just not there. As I've found looking around hitherto there seems to be very little discussion/explanation and info about TT earth installations and its sounding like there may be complications that are not normally considered or obvious to the layman. Or that could just be professional fog blowing around...I'll keep looking.
 

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Discussion Starter #16
From memory an earth rod and clamp is something like a tenner form screwfix, so as long as it's not a huge expanse of concrete, no big deal to put one in.
More than happy to put more earth rods in if necessary, just would like to understand the best way before asking for them. Linked or separate and why.
 

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Yeah, you're right Carty, that's how they sell it. But in my case obviously I have an earth rod system anyway so I'm less clear if their clever work around will work in my scenario. As Freddym says, I'll probably have to ask them directly - happy to do that although always slightly wary of asking a supplier if their offering would be any good, the incentives for them to give a rounded view are just not there. As I've found looking around hitherto there seems to be very little discussion/explanation and info about TT earth installations and its sounding like there may be complications that are not normally considered or obvious to the layman. Or that could just be professional fog blowing around...I'll keep looking.
Of course, it is best to double check with the manufacture of the unit every time.
I just find it a little odd that Zappi would put their necks on the blocks ( so to speak ) by saying their system does NOT need an earthing system for their units ?.
Surely they could not safely say this before knowing what each customers existing system was equipped with regarding earthing rods etc.
Not unless it did not matter of course.
I don’t really understand the technical facts on this subject sorry, just trying to get my head around the whole issue ?.
 

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Out of curiosity I looked at some of the zappi documentation online. They do say that TT systems are handled differently (from the more common TN).

The manual for the v2 has this in it - note the last paragraph:

Earthing
The zappi unit must be earthed in accordance with local regulations.

When installed on a PME (TNC-S) electrical system it is necessary to protect the consumer from a potential electric shock that could occur if the combined Neutral and Earth (PEN) conductor on the supply becomes damaged or disconnected.

zappi includes an additional automatic disconnection device which satisfies the requirements of section 722.4.11.4.1(iii) of BS7671:2018 (the 18th Edition IET Wiring Regulations). This protection device
a) monitors the supply to identify if there is a problem with the PEN conductor and
b) disconnects the supply if a situation arises where the end user might suffer an electric shock
This means that the zappi can be installed without the need for an additional earth rod.

However, if the customer or local regulations require that an earth rod is installed (for instance as part of a TT earthed system) then this should be connected to the dedicated terminal on the main circuit board using a ring terminal (as shown below).


And the datasheet (doesn't say if for v1 or v2) says:

Earthing Arrangement
TN : can be connected to the PME supply. Complies with BS 7671:2018, 722.411.4.1 (iii)
TT : earth resistance < 200 Ω according to BS 7671:2018, or < 100 Ω for some vehicles


That all sounds to me that you will need an earth rod for the zappi on a TT.
 

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Discussion Starter #19
However, if the customer or local regulations require that an earth rod is installed (for instance as part of a TT earthed system) then this should be connected to the dedicated terminal on the main circuit board using a ring terminal (as shown below).

And the datasheet (doesn't say if for v1 or v2) says:

Earthing Arrangement
TN : can be connected to the PME supply. Complies with BS 7671:2018, 722.411.4.1 (iii)
TT : earth resistance < 200 Ω according to BS 7671:2018, or < 100 Ω for some vehicles


That all sounds to me that you will need an earth rod for the zappi on a TT.
Thanks for that Mike, and yes agree that's what it sounds like. Not clear though if/why there should be a separate earth rod for the Zappi if there's an earth rod connected to the CU. I'll ask MyEnergi now...
 

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Not clear though if/why there should be a separate earth rod for the Zappi if there's an earth rod connected to the CU.
The ground is not a uniform 0 volt lump. It has resistance and as currents flow different areas can be at different voltages. Quadrupeds are rather susceptible to electric shock and in some fault conditions there can be enough voltage difference between their front and back legs to kill them - not uncommon with cows on farms.

Hence the term 'equipotential zone' where the same earth voltage is assumed to be the case, e.g. Inside a house. Once outside that 'cage' all bets need re-evaluating.

So a remote building may well need its own earth, and it may not be desirable to connect that back to the house earth. If there is slight difference in ground potentials for significant periods a continuous current could flow and overheat the earth conductor.
 
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