Electrical Diversity and Load Curtailment (EVC) webinar questions and answers

Following our webinar on 28 July 2020 on the topic of Electrical Diversity and Load Curtailment (EVC), we were inundated with your questions. Here you can find the answers.

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.

Find out more about Electricians EngTech.

Your questions answered

Could we change the charging time of EV at home usage to night time when the load is minimum?

We cannot be certain but with smart metering supply companies may offer lower tariffs when demand on the network is low.

The current guidance is that from 2025 at the latest, no new homes should be connected to the gas grid.

They should be heated using low-carbon energy sources. Meaning going forward heating could be derived from heat pumps, electric boiler and/or Solar heating systems.

Currently the guidance in the electrical wiring regulations says no diversity is allowed to heating and as the replacements will more than likely be an electric solution the loads are going to get quite big for housing developments and would there be any scope to apply a form of diversity standalone electric boilers or an electric central system.

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.

In the On-Site Guide/Guidance Notes, are the values for determining maximum demand reliable? Do these values/guidance change and if yes how often?

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.

Have PME DNO supplies been prohibited?

They have not and are the most commonly used earthing system for new supplies.

Are PME DNO supplies unsafe?

No but we need to take precautions when charging electric vehicles when they are outside.

Is there going to be follow up to this to cover DNO, type of supplies and distribution, etc. for say Railway Station Car Parks?

Nothing planned for car parks but the next webinar is going to be on earthing.

Is there a rule of thumb for diversity across a ring circuit?

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.

Are diversity factors standardised or being used as per in engineering practice. Could you please clarify?

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.

Is it a must that you check the incoming supply is up to spec with the DNO before installing EV charge point?

Most definitely yes. It is a requirement of BS 7671: see Regulation 134.1.1.

Are all DNO's happy to accept a wireless load control solution? (i.e. wireless link from CT to charging point)

The DNO needs to be informed of the extra load but the load curtailment equipment is usually the property of the consumer.

What diversity can be applied if the design is for say block of flats requiring number of charging points?

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.

How would diversity be applied to a heat pump?

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.

Why is it so difficult to get the maximum demand for general buildings from the service providers?

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.

What are DNOs doing in regards to increased load on the grid. We have an ageing supply system which may well not cope with additional demand being placed upon it. (For instance a whole street of EVs being charged overnight?

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.

How does this work with either solar / CHP when installed? Do authorities look at this differently like Ground Source?

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.

Are heat pumps all inverter units that cause a lot of disturbance and could also affect installation RCD's?

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.

Can load profiles for maximum demand be easily monitored in commercial installations?

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 I'm carrying out an EICR I often carry out a diversity calculation when filling in max demand on the certificate. The guidance in the On-Site Guide almost always results in the max demand being well over the supply fuse size of 60 amps. Even when using the 40% diversity recommended on the 2391-52 course by the tutor it's often over by 15 or 30amps.

I assume that if there is no sign of overloading/heating of the supply head/cable etc I am not going to be applying a code on the EICR.

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.

How are the supply authorities planning on dealing with the huge demand that EV chargers are going to produce? Will the standard 80A domestic cut out be upgraded?

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.

What is the max. Demand? Is it the connected load multiplied by a diversity factor?

The maximum demand is the sum of the connected loads multiplied by a factor for diversity.

Can I design the protective device rating which is higher than the max demand current?

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.

It was mentioned that if the load exceeds 60A it will be necessary to contact the DNO (or select a charger with load curtailment function).

Can you clarify do you mean the additional load exceeds 60A or the overall load (which typically would be around 80A) from the DNO?

What about the impact on the DNOs supply – typically for non-electric htg, they allow diversity of 2 kVA per house?

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.

I'm keen to get a better insight into commercial, education etc diversity as opposed to Residential. Could you suggest any points of reference in this regard or examples?

BSRIA and CBSE have some very good guidance on the subject.

Is it worth discussing Array charging solutions for non-domestic scenarios?

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.

Now that the buildings are becoming more "all electric" in nature due to carbon strategies etc. Is it likely that diversity will be reviewed?

This is proving difficult regarding electrical demand calculations given these are less common methods at present.

Do you know of any diversity or benchmark guidance documents that could be referred to?

BSRIA and CBSE publish very good guidance on this subject.

Using a washing machine example: Shouldn't RMS ("thermal equivalent") load be used rather than mean?

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.

Can I assume that overload does not necessarily need to be applied to a dedicated circuit for EVSE?

From a design concept you could use an upstream breaker for fault rather than overload protection?

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.

What is the difference between Mode 3 and Mode 4 charging?

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.

Is 5A only to be added if the cooker is plugged into an outlet? If the cooker is directly connected to a cooker switch does this not apply?

The 5A applies when the cooker panel has an integral socket.

Sometime ago there was talk of the equivalent "full fibre" for electrical chargers namely 3phase supplies, is this still being looked at?

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.

How does the charger reduce the current from a fixed load demand from the EV?

By communication between the vehicle and the charging point.

Why would one want to use a split load board now all circuits are required to have 30mA earth leakage? Are they not something from the thought it was unsafe to knock the lighting off for a power circuit fault?

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.

Is load curtailment equipment currently available on the market? Such as the clamp-on monitoring system shown in the presentation.

Yes. The current coil monitors the total load so the demand can be regulated by the load curtailment equipment.

What should the response time be for the load limiting function of the EV charger?

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.

Would multi-occupancy properties cover small hotels and B&Bs for guidance on max demand?

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.

Are Electric vehicles and their batteries going to be used as part of the supply network in periods of high demand on the grid and how would this affect the load calculations of a dwelling?

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.

What is the current thinking regarding the maximum demand for EV charging points where there are a number of these being installed? For example a multi-storey car park?

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.

If it is planned to install an EV charger in a large commercial property, would maximum demand for the entire installation need to be calculated or would it be best to use a data logger?

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.

What if more than one EV chargers are installed, both with load curtailment. Can these be configured so that they don't "fight" each other?

They can be set up to give preference to priority loads.

How can you have confidence in the potential load being accurate when the DNO can't confirm the protective device rating in their own cut-outs with certainty?

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.

I am aware that PODpoint do a load limiting twin outlet car charge unit. 2X32A but limits to 40A MD. Are there any others load limiting charger manufacturers that the presenters know of?

There are other manufacturers who provide load limiting charging equipment.

If we get very clever with load management so a 100A supply is running at 99A all the time will the suppliers' equipment support this load?

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.

What technology is usually used on Demand Monitoring? I have heard Bluetooth or RF Smart Meters struggle over 10m distance. Does this device suffer the same?

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).

How much of this programming is engineering locked, or open to consumer to be able to change it post installation, considering how much these EV affect maximum demand on a domestic installation?

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.

Why is lighting still 100w per lampholder, when this is out of date with current LED lighting?

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.

If we don't have a car charge manufacture at the start of design and no details on any load curtailment, what load is to be allowed?

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.

Does breaking the supply to EV chargers disrupt their comms and possibly contribute to charger defects?

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.

Do you consider the DNO distribution network as it stands robust enough to withstand EV Vehicle charging demand?

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.

Are there still peak and off peak rates?

There are variable rates, dependent on the consumer's agreement with their provider (which is not necessarily the same as the DNO).

Does the country have enough electrical energy to supply the additional electrical vehicles as the market expands? And can you see a point where given the growing demand, the DNO will be compelled to upgrade their network?

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.

Is a minimum of 2.5mm2 PVC cable for CPC a must, or can a 1.5mm2 PVC cable be used and why?

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.

Are chargers currently on the market with load curtailment technology?

Yes.

Will vehicles, in time, have stored journey profiles to help give chargers an idea of min charge needed? This could help to reduce amount of power delivered from more than one charger in an installation.

Thank you for that suggestion, we will pass that on to the IET's Automotive team for further consideration.

Would another option be to install local generation to avoid exceeding the network connection capability such as solar/wind with battery back-up?

Yes, but this may have the impact of increasing overall maximum demand. It may also require the installation of local energy storage.

With understanding maximum demand for a home, is it better to log load over a week to a month and de-aggregate the load data?

The designer should consider that logging over such short periods will not show seasonal variations.

Are the diversity assumptions in the On-Site Guide appendix A still valid?

The IET are reviewing these at the moment, and they may be updated at the next revision.

What design considerations and diversities should be allowed for within commercial developments with a large EVC installation/requirement?

That is a matter for the designer, and might involve modelling to address projected usage for a particular application.

How long should data logging be used for it to be representative? We normally specify 2 weeks?

The designer should consider that logging over such short periods will not show seasonal variations.

Is there any efficiency difference in slow charging or fast charging for Electric vehicles? Or are they both equally effective?

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.

Should the installation, diversity and load curtailment for EV charging be considered for a multi-story building with respective tenant car parking in the same building?

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.

Is there guidance for diversity between buildings for a site with multiple building type uses? E.g. commercial, residential and industrial?

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).

Is Maximum Demand the (total) connected load or is it the maximum demand that can be expected from the installation, e.g. including diversity?

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 chargers require an earth electrode. In a situation where there are a row of terraced houses, could problems arise with regard to overlapping of the earth resistance fields of the electrodes in close proximity to each other?

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.

Will electric vehicle charging run the power system to an unstable condition at peak hours?

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.

In larger houses with several large loads (home heat pump, swimming pool heat pump, EV charger, cooling etc.) can load curtailment be allowed for, in maximum demand calls for loads other than EV charging?

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.

Is there any guidance for connecting EV charging points less than 13.8 KVA to a domestic supply cut-out of 63A or less with off peak electric heating?

Not at present, this is an issue for the designer to consider.

For multi-occupancy blocks of flats, diversity over a number of flats. Are there any tables for this?

What about smart chargers that can back feed into the grid? I know there were schemes such as Electric Avenue looking into this?

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).

A lot of guidance focus on single phase systems. However, I have been questioned about fitting 22kW chargers. How are the DNO gearing up for this?

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.

When a new-build has been installed with extended 16mm tails and a 60amp fuse, how could you install two EV chargers without extensive work to upgrade the incoming mains supply? Surely 25mm tails should have been installed as per BS 7671?

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.

For a large residential tower block with EV charging car-parking, what diversity should be applied without load balancing DNOs recommend different figures?

That is a matter currently for designers and individual DNOs.

Is the load curtailment applicable to an on-street charger?

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.

Regarding diversity for blocks of flats, would it be appropriate to give an overall diversity to size switchgear and cables serving the block of flats (rising mains or laterals and how would that be calculated)?

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).

If there is a large uptake in EV charging in a particular area will the DNO refuse a supply upgrade to a specific household to accommodate EV charging?

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.

What are the standard sizes (kW) of EV charging units commonly installed in domestic properties?

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.

What modes are for DC charging?

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.

How are the diversity factors applied when single phase loads are connected to a 3 phase system?

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.

Is this applicable to domestic properties only? In commercial settings, there could be many chargers running concurrently, hence the need to curtail heating/cooling demand (e.g. office high-rise building)

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.

What is the main difference between connected load and maximum demand and diversified load? Sometimes they are incorrectly used interchangeably.

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.

Is the Demand Monitoring Unit available? Is a typical cost known for this device?

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.

There are some chargers that are link to the current actual demand of the property and will limit the maximum amount of charge to within 98% of the pre-set total demand. As load are switched out/off, the charger will ramp up its output. Is that reflected in BS 7671 (311)?

This is not precluded by BS 7671.

Why has the risk assessment/rationale not been included in the model risk assessment of annex B etc?

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.

Does not the vehicle tell the charger what its maximum demand will be? Some vehicles only have a 3.5kW inverter fitted.

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.

Are you aware whether DNO's have published figures for after-diversity maximum demand (ADMD) for dwellings with EV charging, in order to size transformers for a large residential development?

That would be a question for DNOs or ENA.

Are the load curtailment measures noted regarding EV charging loads now accepted by utility providers?

This is a question for individual DNOs at present.

I think the maximum demand should be linked to half hourly energy rate for domestic customers in the future.

This will encourage customer to think about use electricity more diversity manner. Still little encouragement from the regulator to enforce the domestic energy suppliers to install smart metering and provide the half hourly day ahead rating.

What the steps taken by IET as an organisation in this regard to expedite the smart metering process?

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.

If the DNO supply is a bit flaky, would a client be likely to find their charger has switched itself off overnight and vehicle has insufficient to charge to get client to work in the morning?

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).

Do any EV chargers allow the user to input an anticipated charging time available so that it can workout most efficient charging profile compared to available capacity?

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.

Does the design need to take into account the plan to phase out gas-fired boilers?

BS 7671 and its guidance is not so specific. Legislation can affect the design, and future acceptability, of an electrical installation at any time.

If design is based on manufacturers' information does this mean that installation has to be re-designed if/when an EV charger is replaced at end of life?

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.

Why is it bad to stop charging mid way? When power returns, does the charge not carry on?

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).

From previous (limited) experience, the load assessment at design stage is 10 out of 10 times much greater than the actual Maximum Demand Peak Load of the actual installation when it is in use by using the on site guide Diversity figures.

What is your view on this? Are we allowed to take a slightly more realistic approach?

Work is on-going to review this, as it has been recognised that modern loads are not accounted for.

What type of RCBO do we have to use for the car chargers?

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).

Re: the heating assessment saying that the 'cable would be sized on the 10A + 30% +5A Iinc. socket'. I assume that that isn't the case for the final circuit cable, but is used for the total max. demand?

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.

Why is the commentary on the Wiring Regulations not being revised?

The copyright of the book belongs to the original author, Paul Cook.

You stated that you can apply diversity to a cable size, say for a shower, at design stage. However I always understood that equipment supply wiring should be sized as per the full load, as it may use the full load at some time?

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.

What are the pros and cons of Demand Factor v Load Factor?

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.

Based on a diversity factor of 1 in a scenario of the industrial socket outlets, if you have an installation of 10 no. 63A SP&N sockets in a building what would the maximum demand be? Realistically it's unlikely you would need a 630A SP&N supply, as not all the sockets would be fully utilised at the same time.

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.

Shall we select cables & wires based on connected loads or maximum demand for EV's charging?

Knowing the maximum demand then allows the designer to assess the existing spare capacity.

Which one is more power saving conventional charging or induction "remote" charging which is available today at market?

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.

Is there any rule or best practice values for diversity Factor to size Transformers used in indoor substations?

This is outside the Scope of BS 7671.

Would you size the charge controller based on diversity as well?

Diversity would be applied to the electrical installation. The charge controller is sized in accordance with its required operating parameters.

Will IET offer training in the future?

Please visit IET Academy for current and future online courses. IET no longer offers face-to-face training for electrical subjects.

Will diversity of a commercial large scale 2 phase installation be discussed or just 100 Amp SP domestic?

Diversity can be applied across different types of installations, this webinar wasn't directly focusing on any particular type.

When using smart chargers to manage or curtail EV charging load to ensure maximum demand is not exceeded because these rely on settings which may be held in software and may depend on communications links which could fail, is there a need for additional measures to protect against the risk of supply overload if the EV charger fails and does not manage or curtail load as expected?

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.

Are there guidelines for what percentage diversity should be applied to apartments or commercial premises with a central metering location?

Demand factors for different types of installations were published in IET's Commentary to BS 7671. This book is copyright of the author.

Does the IET offer clear guidance on the connection for EV charging and earthing arrangement.

See IET's Code of Practice for Electric Vehicle Charging Equipment Installation, 4th Edition, published March 2020.

When diversity & maximum follow all regulations and not common sense they are over sized we have the information on similar building with the utility companies let start sharing and using.

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.

On model forms is it max demand on form with diversity taken in to account.

Yes

What is the power factor of a EV vehicle?

You'll need to contact the manufacturer of the vehicle in question.

Can I get detail example for slide 11 please?

For more information related to this table, see Appendix A of The IET's On-Site Guide (2018)

Noted that on maximum demand selection IEEE 141 provides guidance in terms of selection of continuous, intermittent and standby duty in terms of selection peak demand, has this been a consideration in terms of the assessment of maximum demand assessment?

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.

Will hot tubs installation be considered in future discussions, as there are a lot more hot tub installations encroaching on max demand and there is still no clear guidance?

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.

What impact will demand side response have on maximum demand.

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.

Picking up on this query, would be useful for the IET to provide diversity guidance on large offices and commercial developments. Is there any historical information from DNO's?

Such information was published in IET's Commentary to BS 7671. This book is copyright of the author.

EV Chargers require a local earth electrode. In a situation where there is a row of terrace houses, would there be a problem of overlapping of the earth electrode resistance fields? Thank you. Colin Price. London Borough Of Havering Technical Services.

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.

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.

Will electric vehicle charging run the power system to an unstable condition at peak hours?

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.

Will not the RCCB require overload protection if the load can exceed its rating and the upstream OCPD is rated higher than the RCCB rating?

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.