Electrical Vehicle Chargers - No Diversity?

Apostolos said:

Its clearly stated in BS7671 that no diversity should be applied to an EVC

This is not the case ... it was in 2018, but in 2020 (Amendment 1) it was updated:

722.311 Maximum demand and diversity
722.311.201 Load curtailment, including load reduction or disconnection, either automatically or manually, may be taken into account when determining maximum demand of the installation or part thereof.

Yes, but in the absence of a load management system it's still zero diversity.

pww235 said:

Yes, but in the absence of a load management system it's still zero diversity.

BS 7671 does not prohibit diversity for EV charging points.

The application of diversity will depend on the individual installation.

Diversity in general is applied:

(a) to circuits, and

(b) to parts of the installation, and the installation itself (effectively, switchgear, submains, etc.)

NOTE: Each EV charging point must be on its own final circuit ... BUT that final circuit may be within the charging equipment itself. This analogy should not really be applied for domestic charging points in general, but in terms of commercial/industrial/public charging equipment, there may be more than one charging point per item of charging equipment. So, there are a number of cases where one submain or feeder pillar etc. feeds many charging points.

In installations where EV is a significant proportion of the load of the installation, or swtichboard/distribution board/consumer unit, then it's unlikely to be able to apply diversity, especially if it's impossible to make "time of use" type assessments.

In larger installations, if a designer's modelling shows that it is highly improbable that overloads will occur, BS 7671 does not prevent that -- but that is at the designer's own liability.

In practice, many charging points in domestic installations are being installed with load control these days, to spread more widely the available power, and also larger installations are beginning to take advantage of that (for example, may be much better for a business whose employees work 8 hours per day to offer on average curtailed, or even fully-curtailed, i.e. 3 kW only, charging for employees' vehicles during the day)

pww235 said:

Yes, but in the absence of a load management system it's still zero diversity.

BS 7671 does not prohibit diversity for EV charging points.

The application of diversity will depend on the individual installation.

Diversity in general is applied:

(a) to circuits, and

(b) to parts of the installation, and the installation itself (effectively, switchgear, submains, etc.)

NOTE: Each EV charging point must be on its own final circuit ... BUT that final circuit may be within the charging equipment itself. This analogy should not really be applied for domestic charging points in general, but in terms of commercial/industrial/public charging equipment, there may be more than one charging point per item of charging equipment. So, there are a number of cases where one submain or feeder pillar etc. feeds many charging points.

In installations where EV is a significant proportion of the load of the installation, or swtichboard/distribution board/consumer unit, then it's unlikely to be able to apply diversity, especially if it's impossible to make "time of use" type assessments.

In larger installations, if a designer's modelling shows that it is highly improbable that overloads will occur, BS 7671 does not prevent that -- but that is at the designer's own liability.

In practice, many charging points in domestic installations are being installed with load control these days, to spread more widely the available power, and also larger installations are beginning to take advantage of that (for example, may be much better for a business whose employees work 8 hours per day to offer on average curtailed, or even fully-curtailed, i.e. 3 kW only, charging for employees' vehicles during the day)

Yes, the installation as a whole may have diversity applied, and if a load management system is employed then that can be used to limit the loading by setting a maximum power consumption for the EV chargers that is lower than their rated delivery. But in the instance of the original post, a TPN distribution board supplying 5no. 32A TPN chargers, no diversity should be applied to the EV circuits when calculating the total DB load and it's submains cable....unless there's load management.

pww235 said:

But in the instance of the original post, a TPN distribution board supplying 5no. 32A TPN chargers, no diversity should be applied to the EV circuits when calculating the total DB load and it's submains cable....unless there's load management.

Well, I'm almost with you and tend to agree in most cases with such a small number it's probably best not to apply diversity just in case all chargers were to start the cycle and request full 7 kW at the same time ... but BS 7671 doesn't specifically say you can't

It remains the case that 7 kW chargers in use don't use 7 kW all the time, and even with < 10 no. chargers, we might think about models to consider the probability of all charging points demanding full load at the same time.

The situation is complicated by the fact that in some situations, the concurrent max load draw being requested is more likely than others.