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This webinar was arranged by the IET’s Electrician EngTech programme in association with Wiring Matters. Electrician EngTech helps electricians gain recognition of their professional competence.
We cannot be certain but with smart metering supply companies may offer lower tariffs when demand on the network is low.
Yes we agree that is the most probable replacement for gas and oil boilers together with improved insulation for buildings.
We think load curtailment will need to be used to match loads to available supplies.
The On-Site Guide and the Guidance Notes change with each edition of the Wiring Regulations. We are already looking at these updates now to coincide with Amendment 2 to BS 7671:2018.
They have not and are the most commonly used earthing system for new supplies.
No but we need to take precautions when charging electric vehicles when they are outside.
Nothing planned for car parks but the next webinar is going to be on earthing.
Loads ideally need to be spaced as evenly as possible around a ring final circuit with the largest loads in the centre. There is guidance for diversity for socket circuits in the On Site Guide.
The IET On Site Guide and IET Guidance Note 1 offer methods to calculate this. Other industry norms are available from organisations such as CIBSE.
Most definitely yes. It is a requirement of BS 7671: see Regulation 134.1.1.
The DNO needs to be informed of the extra load but the load curtailment equipment is usually the property of the consumer.
The designer would need to match the loads to the available supply with no diversity applied. However, you can use intelligent charging points that communicate with each other to modulate the demand.
You would not apply any diversity to the circuit to the heat pump. The circuit protection and the cable should be rated in accordance with the equipment information or manufacturer's data sheet. For overall diversity no diversity allowable but the use of load curtailment could be applied.
Maximum demand would need to be calculated by the designer not the supplier. An application is then made to the supplier for the supply. The supplier will determine the Authorised Supply Capacity (ASC) which should not be exceeded.
We know that at least one DNO is considering moving towards supplying 3 phase as a standard to houses. DNOs may use Smart Meters to ration demand in times of high demand. The requirement to notify the ENA or the DNO when installing EV charging may lead to the DNO refusing to allow for the extra load or permission may be given if load curtailment is installed.
Feeding in to the network from CHPs and Solar assists with the capacity of available supply. It is a high probability that most vehicles are likely to be charged at night so Solar will not be available. CHPs are usually designed to deliver the base load for the installation and not to export to the grid. Prosumer installations are likely to be considered soon, where the consumer may be a user and a supplier.
Yes. Inverter drives produce harmonics and this would need to be considered when carrying out cable calculations. Any DC component produced by the inverter may lock up Type AC RCDs so the use of Type A RCDs should be considered. A lot of manufacturers now supply Type A RCDs as standard.
Yes. BS 7671 Regulation 134.1.1 requires the designer to consider the rating of the supply to be verified before adding any additional loads. Power logging the supply for an extended period is a good way of verifying the supply can take any additional load.
If an EIC is available for the installation, the designer will have calculated the maximum demand so you could use that. As part of your Periodic Inspection you will have looked for evidence of overloading as part of the inspection process.
You can either estimate the maximum demand using engineering judgement, or you could use a clamp meter to measure the demand with a good number of appliances switched on to simulate the consumer's usage.
No there will be no need.
We know that at least one DNO is considering moving towards supplying 3 phase as a standard to houses. DNOs may use Smart Meters to ration demand in times of high demand.
The requirement to notify the ENA or the DNO when installing EV charging may lead to the DNO refusing to allow for the extra load, or permission may be given if load curtailment is installed.
The maximum demand is the sum of the connected loads multiplied by a factor for diversity.
Yes. However, you need to ensure Ib≤In≤Iz so the cable needs to be rated for the rating of the protective device.
It is very sensible to do this for distribution circuits so that additional loads can be added at a later date.
If the total load including the vehicle charging point exceed 60A then permission must be sought from the DNO before installation. Less than 60A then the ENA needs to be informed within 30 days.
This is the reason for informing the DNO before installation in order that they can determine if there is capacity on the local transformer.
BSRIA and CBSE have some very good guidance on the subject.
The designer would need to match the loads to the available supply with no diversity applied. However, you can use intelligent charging points that communicate with each other to modulate the demand.
BSRIA and CBSE publish very good guidance on this subject.
The thermal equivalent would be to calculate the RMS value of current by collecting all the peak values of current over a period of time. The mean value gives a good indication of the thermal equivalent.
You do not need to provide overload protection for a fixed load. However the cable would need to be rated in accordance with BS7671 Regulation 433.1.1.
Mode 3 connects the vehicle to an AC charging point with a control function between the vehicle and the charging point. Mode 4 is where AC is converted to DC in the charging point equipment to charge the vehicle with DC.
The 5A applies when the cooker panel has an integral socket.
We have not heard this term. 3 phase charging equipment is quite common. Mode 4 "Rapid" chargers are the fastest at the moment, but require large three-phase supplies. They would be most suitable for rapid charging in places like motorway service stations, filling stations, etc.
By communication between the vehicle and the charging point.
It is perfectly acceptable to use dual RCD boards to supply domestic installations with the circuits split over 2 or more RCDs. However, the leakage current should not exceed the requirements of Regulations 314.1 and 531.3.2.
Yes. The current coil monitors the total load so the demand can be regulated by the load curtailment equipment.
The operation of such equipment is currently a matter for the designer, and must be sufficient to coordinate with upstream devices, and also coordinated with switchgear and control gear assembly ratings. It is acknowledged that in any installation with diversity applied, it may be possible to exceed the maximum demand on occasion.
We agree that an issue with electronically-managed load curtailment, different to simply load-shedding by switching, is that there is a time-lag between the demand change and the curtailment being made - and the method of achieving curtailment must of course try and avoid switching surges.
As a result, there could be an impact on network stability. Therefore, there may be future updates to ENA Engineering Recommendation G100, which currently only covers export limiting schemes, to include for controls and features import limiting schemes.
No. each dwelling should be considered with the landlords loads. Diversity will vary with the number of properties in a block.
The larger the number the greater the level of diversity can be applied. DNOs issue guidance on this.
The use of vehicle to grid supply is being proposed so vehicles can act as energy storage systems. Protocols and tariffs have not been decided on as far as we know.
The designer would need to match the loads to the available supply with no diversity applied. However, you can use intelligent charging points that communicate with each other to modulate the demand.
Yes the use of data loggers is highly recommended to verify the current maximum demand on an existing installation before adding any extra loads. See Regulation 134. 1.1.
They can be set up to give preference to priority loads.
The designer of the electrical installation is responsible for assessing the maximum demand of that installation. When additional circuits are added, or existing circuits change use, the maximum demand may of the installation, or part of it, may need to be reassessed.
There is not necessarily a relationship between the maximum demand that the designer assesses, and the cut-out fitted by the DNO.
There are other manufacturers who provide load limiting charging equipment.
That is a matter for the DNOs. The reason for notification when certain types of system are installed (e.g. EV charging, generation, etc.) is for the DNO to assess their network accordingly.
We agree that some wireless networking devices struggle with some building materials, and this is worse in some premises or areas than others.
Ethernet connectivity using a homeowner's own installation (either wired or WIFI) could also be subject to the homeowner making changes to their network, faults with their networking equipment, etc. Dedicated communications solutions, perhaps similar to those used in industrial applications, may be more robust and reliable, but at the same time would be more expensive.
Whilst these are all issues for the designer to consider, we appreciate that sometimes the solutions offered may be restricted by support of the manufacturer of the electric vehicle supply equipment (charging point).
That depends on the implementation by the charging equipment manufacturer. It is certainly a factor that the Designer and Installer should consider when selecting products.
Yes, the On-Site Guide considers worst-case for guidance. Work is ongoing to review this. The next edition may be updated to reflect the move to LED lighting. The OSG is guidance so a designer can apply his/her own factors using engineering judgement.
That is a matter for the designer. A design decision at an early stage to either assume load curtailment, or even determine the maximum rating of the charging point that can be selected (say to 32 A instead of 63 A) may limit the selection of products (to 7 kVA or less) when a detailed design or installation design is carried out.
Yes. We do not recommend that approach - however, it should be noted that power may be lost to the EVSE under other circumstances, such as faults or supply interruptions, and vehicle manufacturers must address that in their design.
That is a matter for the DNOs. The reason for notification when certain types of system are installed (e.g. EV charging, generation, etc.) is for the DNO to assess their network accordingly.
Studies have been carried out, and we understand most, if not all, DNOs have strategies in place to accommodate EV charging demand.
There are variable rates, dependent on the consumer's agreement with their provider (which is not necessarily the same as the DNO).
That is a matter for the DNOs. The reason for notification when certain types of system are installed (e.g. EV charging, generation, etc.) is for the DNO to assess their network accordingly.
Studies have been carried out, and we understand most, if not all, DNOs have strategies in place to accommodate EV charging demand.
The CPC should be sized in accordance with Regulation Group 543.1. The cable may be less than 2.5 mm2, provided it both:
(a) is selected in accordance with Regulation 543.1.3 or Regulation 543.1.4;
AND
(b) the conductor is either an integral part of a cable, or is contained within a wiring system enclosure, or is formed by conduit, ducting or trunking.
Yes.
Thank you for that suggestion, we will pass that on to the IET's Automotive team for further consideration.
Yes, but this may have the impact of increasing overall maximum demand. It may also require the installation of local energy storage.
The designer should consider that logging over such short periods will not show seasonal variations.
The IET are reviewing these at the moment, and they may be updated at the next revision.
That is a matter for the designer, and might involve modelling to address projected usage for a particular application.
The designer should consider that logging over such short periods will not show seasonal variations.
There are efficiency differences between charging modes due to heat losses. There is an optimum charging speed for efficiency, but this also needs to be tempered against the instantaneous load (the capability for which may not be present in some installations), and long-term damage to the battery.
Whether fast or rapid charging affects the life of the batteries in the vehicle depends on the battery chemistry and battery management system. The battery management system in the vehicle should control the charge speed (by controlling charge current and/or voltage dependent on chemistry) to prevent damage to the batteries and limit the impact on battery life.
For example, a particular battery fully discharged, given 100 kW charge capability, might be able to restore 60% of the charge in 10 minutes, but then reach 90% charge in a further 10 minutes, and 100% in a further 10 minutes. The same battery given 50 kW might take 17 minutes to reach 60% charge, 25 minutes to reach 90% charge, and 40 minutes to reach full charge, and the same battery given 7.4 kW may take 200 minutes to reach full charge.
This is not precluded by BS 7671:2018+A1:2020. Modelling of such a system would be something the designer should consider. It might also be subject to agreement with the DNO, and the subject of a connection agreement.
This is because, with electronically-managed load curtailment, there is a time-lag between the demand change and the curtailment being made - and the method of achieving curtailment must of course try and avoid switching surges.
As a result, there could be an impact on DNO's network stability. There may be future updates to ENA Engineering Recommendation G100, which currently only covers export limiting schemes, to include for controls and features for import limiting schemes.
There is guidance in the following IET publications:
(a) IET Electrical Installation Design Guide (in the 4th Ed 2018, section 3.5, pp36-42).
(b) Commentary on the IET Wiring Regulations (in the 2017 Ed, section 3.3.3, pp45-51).
This is a good question, and it depends what you want the maximum demand for, e.g.:
(a) For an individual circuit to determine the design current, diversity might only be rarely appropriate
(b) To determine the continuous current rating of a final circuit distribution board might consider diversity for the connected circuits differently to the macro-diversity applied for upstream distribution switchboards.
(c) To determine the demand of a multi-occupancy site you might consider demand factors for the whole site differently to individual installations, as discussed in the following IET publications:
- IET Electrical Installation Design Guide (in the 4th Ed 2018, section 3.5, pp36-42).
- Commentary on the IET Wiring Regulations (in the 2017 Ed, section 3.3.3, pp45-51).
EV charging equipment does not necessarily require an earth electrode. Earth electrodes are most-often used by installers who have selected to supply the EV charging equipment from a separate TT system to avoid connection to a TN-C-S (PME) or TN-S earthing system, as a result of Regulation 722.411.4.1 of BS 7671. Only one electrode is required per TT system - so a group of chargers on the same TT system could use a common electrode.
There are dangers involved with providing a separate earthing system, those of:
(a) simultaneous contact of exposed- or extraneous-conductive-parts of the two systems
(b) transfer of potential below ground, as the ground itself is a conductor, although it has some resistance.
Where installers choose to adopt TT for the charge point, overlapping areas of influence of earth resistance are indeed a problem - but this is not limited simply to effects between two close TT earth electrodes, it could be an issue with buried conductive parts (such as extraneous-conductive-parts) of PME or TN-S earthing systems.
Further information on the issues found when providing "TT islands" for charging points, including recommended separation distances below and above ground, is available in the IET Code of Practice for Electric Vehicle Charging Equipment Installation, 4th Ed 2020 - see Annex H principally.
See also this IET Wiring Matters article.
That is really a question to be posed to the Distribution Network Operators. However, research has been ongoing for a number of years, and DNOs are preparing for the change in network usage. It is also the reason that the installation of charging equipment should be notified to the DNO - see Section 11 of the IET Code of Practice for Electric Vehicle Charging Equipment Installation, 4th Ed 2020.
There is no reason this approach can't be used, provided of course it is recognised by the DNO. Installers have for many years, for example, been arranging switching or contactors to prevent two electric showers being used simultaneously in the same property.
One issue with electronically-managed load curtailment, different to simply load-shedding by switching as just described, is that there is a time-lag between the demand change and the curtailment being made - and the method of achieving curtailment must of course try and avoid switching surges.
As a result, there could be an impact on network stability. Therefore, there may be future updates to ENA Engineering Recommendation G100, which currently only covers export limiting schemes, to include for controls and features import limiting schemes.
Not at present, this is an issue for the designer to consider.
There is guidance in the following IET publications:
(a) IET Electrical Installation Design Guide (in the 4th Ed 2018, section 3.5, pp36-42).
(b) Commentary on the IET Wiring Regulations (in the 2017 Ed, section 3.3.3, pp45-51)
This is not precluded in BS 7671. Amendment 1:2020 to BS 7671 includes a requirement (Regulation 722.551.7.2) for the type of connector that is used to prevent a "live plug pins" situation. Design considerations for "vehicle to grid" as it is sometimes called, are covered in Section 10 (Vehicle as storage) of the IET Code of Practice for Electric Vehicle Charging Equipment Installation (4th Ed 2020) - this should be read in conjunction with the IET Code of Practice for Electrical Energy Storage Systems (2nd Ed expected December 2020).
That would be a question for individual DNOs as they are all separate commercial entities. Installation of charging equipment of this rating would require advance notification to the DNO (see Section 11 of the IET Code of Practice for Electric Vehicle Charging Equipment Installation, 4th Ed 2020) to permit them to check the impact on that particular part of their network.
Load curtailment could be used, but this may seriously affect the charging times of two charging points in use simultaneously, and of course a supply upgrade would be the best option. Of course, this is something that designers of future developments should be considering, and hopefully enforced by legislation in the future.
There may be existing developments, designed a number of years ago, still to come into service, however.
That is a matter currently for designers and individual DNOs.
It is not precluded by BS 7671, but individual DNOs may have their own views due to the impact on their networks.
One issue with electronically-managed load curtailment, is that there is a time-lag between the demand change and the curtailment being made - and the method of achieving curtailment must of course try and avoid switching surges. As a result, there could be an impact on network stability. Therefore, there may be future updates to ENA Engineering Recommendation G100, which currently only covers export limiting schemes, to include for controls and features import limiting schemes.
This is possible, although the factors used would depend on the types of loads in use in the installations. Guidance is in the following IET publications:
(a) IET Electrical Installation Design Guide (in the 4th Ed 2018, section 3.5, pp36-42).
(b) Commentary on the IET Wiring Regulations (in the 2017 Ed, section 3.3.3, pp45-51).
We understand that DNOs have committed to upgrade dwellings to 100 A per phase. Above this, that would be a question for individual DNOs.
Any installation whose demand exceeds 13.8 kVA requires notification to the DNO prior to installation of the equipment.
Most domestic chargers are 32 A single phase (7.4 kW). Due to the DNO notification requirements, it is currently rare to see larger units being installed in dwellings.
Mode 3 is AC charging.
Mode 4 is DC (or "rapid") charging.
Both Modes 3 and Mode 4 chargers are permitted by the standards to include demand curtailment communications as described in the webinar presentation.
There is no difference in how diversity is applied, although the designer will have to consider:
(a) Difference in relationship between line current and kVA is 1:1 in single-phase circuits, and 1:3 in three-phase circuits.
(b) Balance of single-phase loads (and demand-over-time) across phases. Use of load profile modelling is necessary to check this.
No, BS 7671:2018+A1:2020 permits load curtailment to be used for EV charging equipment in all premises. However, modelling of anticipated usage would have to be taken into account to determine whether this is feasible in particular circumstances, considering human behavioural factors. For example, offices that operate "9 to 5" could be subject to a number of employees arriving and plugging in their vehicles in a short period at the start of the working day, as the building demand also starts to increase. The impact of curtailment on charge times might need to be considered in this case.
Charge times for employee parking slots could be more heavily curtailed than visitor spots.
At the same time, however, employees might need to make personal appointments in their lunch break, that they have to drive to ... if their vehicle has not been able to charge, this could be problematic.
One issue with electronically-managed load curtailment, different to simply load-shedding by switching as just described, is that there is a time-lag between the demand change and the curtailment being made - and the method of achieving curtailment must of course try and avoid switching surges.
As a result, there could be an impact on network stability. Therefore, there may be future updates to ENA Engineering Recommendation G100, which currently only covers export limiting schemes, to include for controls and features import limiting schemes.
In some cases they are one in the same thing, although BS 7671 uses only the terms maximum demand and design current in relation to sizing relative to the load. (Diversified load is not used at all in BS 7671, and connected load is used in two cases to describe the fact that a load might have an effect on either RCD nuisance-tripping or the operation of a generating set.)
The difference in the use of maximum demand for a whole installation, or part of an installation, or an individual circuit, will depend on what you are using the information for.
For example, when sizing the design current Ib of an individual final circuit, which may need to take into account the peak load current to prevent operation of the overcurrent protective device, use of the maximum full load current may be appropriate.
Demand monitoring units are not available for all charging points, and obviously less expensive charging points are less likely to include for functionality.
The functionality has to be implemented by the charge point manufacturer. The demand monitoring unit has to be compatible with the charging point, and pricing is a question for individual manufacturers.
This is not precluded by BS 7671.
The checklists in Annex B, D and E contain the question "is the existing supply adequate for the additional demand?" or similar.
The Risk Assessments in Annexes B to E are purely aimed at earthing arrangements due to the particular shock risks that may be presented by that scenario, and are not intended to be used in place of a more comprehensive CDM Risk Assessment that should be carried out for every installation.
The charging equipment tells the vehicle the maximum current available for charging. The vehicle may use less than the maximum the charging equipment says is available.
That would be a question for DNOs or ENA.
This is a question for individual DNOs at present.
One issue with electronically-managed load curtailment, different to simply load-shedding by switching as just described, is that there is a time-lag between the demand change and the curtailment being made - and the method of achieving curtailment must of course try and avoid switching surges.
As a result, there could be an impact on network stability. Therefore, there may be future updates to ENA Engineering Recommendation G100, which currently only covers export limiting schemes, to include for controls and features import limiting schemes.
Work is ongoing in the IET to review maximum demand and diversity.
For some purposes, application of diversity in terms of half hourly demand may not be appropriate. However, for whole premises, it may be.
That is a possibility. Some vehicles stop the charge cycle completely if power is "lost", i.e. communication between charger and vehicle stops (rather than curtailed, where communication remains open).
The actual current drawn is controlled by the vehicle. The charging equipment can set the maximum current available to the vehicle. It is possible to build in functionality to charging points to limit the maximum current available, dependent on the particular tariff, or on a timed basis, or even, for example, as described in the question.
Looking forward, tariffs may be dynamic, and integration with smart metering will permit curtailment when tariffs switch.
BS 7671 and its guidance is not so specific. Legislation can affect the design, and future acceptability, of an electrical installation at any time.
That is a possibility. However, the same issue may arise if someone replaces an oven that was suitable for a circuit protected by a B25 mcb, with one that requires a B32 mcb.
There is no such thing as a "standard" circuit for a particular appliance.
Not necessarily. Some vehicles stop the charge cycle completely if power is "lost", i.e. communication between charger and vehicle stops (rather than curtailed, where communication remains open).
Work is on-going to review this, as it has been recognised that modern loads are not accounted for.
Where there is no protection against DC residual currents in the charging equipment, the installer may use:
- Type B RCD
- an RDC-DD in conjunction with either a Type A or Type F RCD.
Where protection against DC residual currents is included in the charging equipment, the installer may use a Type A or Type F RCD.
In all cases, the RCD must break all live conductors (L+N for single-phase, L1+L2+L3+N for three-phase).
This example is given in the IET’s On-Site Guide, P122, Table A1, for the point of utilisation, i.e. household cooking appliance. The result could be used to size the cable for that application and/or to establish maximum demand for the installation.
The copyright of the book belongs to the original author, Paul Cook.
Diversity should not be applied when sizing the cable for a shower (assuming an instantaneous water heater type). With this type of load, it's either on or off, hence, the cable must be sized to carry the full rated load of the shower.
Demand Factor = Maximum demand / Total connected load
Demand Factor can be used to size conductors; for example, if the total connected load is 100 A but the maximum demand is 50 A, then the Demand Factor = 0.5
Load Factor = Average load / Maximum demand
In the time domain, Load Factor can be used to establish the rate of use of electricity; for example, electrical consumption over a 24 hr period has been 4,600 kWh (20 A) and the maximum demand is 11,500 kWh (50 A), then the Load Factor = 0.4 but is usually expressed as a percentage = 40 %
The main difference between Demand Factor and Load Factor is that the denominator of the Demand Factor is fixed. The Demand Factor, therefore, can only be established with knowledge of the total connected load.
Then the immediate answer here is that the diversity factor, in your scenario, is not 1.
When designing, the client will need to declare what they want to happen and the designer will design the installation accordingly. Whilst I can’t assume the environment that this design would be in use, IET guidance offers that the first socket-outlet be rated at 100 % then all subsequent at 40 %. In your scenario, the maximum demand would equate to:
= 63 + 9(63 x 0.4)
= 63 + 9(25.2)
= 63 + 226.8
= 289.8 A
Therefore, it is extremely important to establish the client’s requirements before starting the design.
Knowing the maximum demand then allows the designer to assess the existing spare capacity.
Whilst the question is outside the scope of this webinar, I would suggest you contact the vehicle’s manufacturer and the manufacturer of the changing equipment in order to assess efficiencies.
This is outside the Scope of BS 7671.
Diversity would be applied to the electrical installation. The charge controller is sized in accordance with its required operating parameters.
Please visit IET Academy for current and future online courses. IET no longer offers face-to-face training for electrical subjects.
Diversity can be applied across different types of installations, this webinar wasn't directly focusing on any particular type.
BS 7671 requires that all selected and installed equipment meets the relevant product standards, it is installed correctly, etc. Like any other scenario, if equipment fails or faults occur, the electrical installation would be designed to remove the fault or overload current as necessary. Beyond that, if there is a concern that equipment may fail in a specific way, the manufacturer's instructions should be followed and/or the installation designed accordingly.
Demand factors for different types of installations were published in IET's Commentary to BS 7671. This book is copyright of the author.
See IET's Code of Practice for Electric Vehicle Charging Equipment Installation, 4th Edition, published March 2020.
Noted.
From a Regulatory point of view, i.e. BS 7671 The IET Wiring Regulations, methods of assessing diversity and maximum demand are not prescribed.
Guidance on diversity and maximum demand errs on the side of caution. IET guidance states “The Guide introduces the use of standard circuits…... However, because of simplification, this Guide may not give the most economical result.”
The designer, who is an experienced person, competent, etc., can use their engineering judgement to design an installation based on exact loads and operating profiles.
Yes
You'll need to contact the manufacturer of the vehicle in question.
For more information related to this table, see Appendix A of The IET's On-Site Guide (2018)
The document you cite, IEEE 141-1993 - IEEE Recommended Practice for Electric Power Distribution for Industrial Plants, is a US-centric publication from 1993 (reaffirmed in 1999). Designers may choose to use this publication on installations in the UK.
In terms of diversity and maximum demand, hot tubs, like any load, should be factored into the electrical design. Other factors, such as external influences, earthing arrangements, etc., also need to be taken into account. One key issue is that an ordinary person can buy a hot tub and simply plug it in, which, of course, raises many safety issues for the user.
It depends when and where the control algorithms are implemented. If it's used to lower demand in the area, then no. If it's used to cap the maximum demand, then yes.
Such information was published in IET's Commentary to BS 7671. This book is copyright of the author.
EV charging equipment does not necessarily require an earth electrode. Earth electrodes are most-often used by installers who have selected to supply the EV charging equipment from a separate TT system to avoid connection to a TN-C-S (PME) or TN-S earthing system, as a result of Regulation 722.411.4.1 of BS 7671. Only one electrode is required per TT system - so a group of chargers on the same TT system could use a common electrode.
There are dangers involved with providing a separate earthing system, those of:
(a) simultaneous contact of exposed- or extraneous-conductive-parts of the two systems
(b) transfer of potential below ground, as the ground itself is a conductor, although it has some resistance.
Where installers choose to adopt TT for the charge point, overlapping areas of influence of earth resistance are indeed a problem - but this is not limited simply to effects between two close TT earth electrodes, it could be an issue with buried conductive parts (such as extraneous-conductive-parts) of PME or TN-S earthing systems.
Further information on the issues found when providing "TT islands" for charging points, including recommended separation distances below and above ground, is available in the IET Code of Practice for EV Charging Equipment Installation 4th Ed 2020 - see Annex H principally.
See also this IET Wiring Matters article.
That is really a question to be posed to the distribution network operators. However, research has been ongoing for a number of years, and DNOs are preparing for the change in network usage. It is also the reason that the installation of charging equipment should be notified to the DNO - see Section 11 of the IET Code of Practice for EV Charging Equipment Installation, 4th Edition 2020.
Yes.
Overload protection of the RCCB cannot solely be based on the use of diversity factors of the downstream circuits. The rated current of the RCCB in the assembly Inc can be established using diversity however, overload protection of the RCCB can require the rated current of the RCCB Inc to be coordinated with the upstream OCPD device, e.g. service fuse-link rated current. Please see Regulations 536.4.202 and 536.4.3.2 for the complete requirements.