EV charging - electrical installation design

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HomeElectric Vehicle chargingEV charging - electrical installation design

Electric vehicle charging is a new load for low voltage electrical installations that can present some challenges.

Specific requirements for safety and design are provided in IEC 60364 Low-voltage electrical installations – Part 7-722: Requirements for special installations or locations – Supplies for electric vehicles.

Fig. EV21 below provides an overview of the scope of application of IEC 60364 for the various EV charging modes.

[a] in the case of street-located charging stations, the "private LV installation set-up" is minimal, but the IEC60364-7-722 still applies from the utility connection point down to the EV connecting point.
Fig. EV21 – Scope of application of IEC 60364-7-722 standard, which defines the specific requirements when integrating an EV charging infrastructure into new or existing LV electrical installations.

It should also be noted that compliance with IEC 60364-7-722 makes it mandatory that the different components of the EV charging installation fully comply with the related IEC product standards. For example (not exhaustive):

  • EV charging station (mode 3 and 4) shall comply with the appropriate parts of the IEC 61851 series.
  • Residual Current Devices (RCDs) shall comply with one of the following standards: IEC 61008-1, IEC 61009-1, IEC 60947-2 or IEC 62423.
  • RDC-DD shall comply with IEC 62955
  • Overcurrent protective device shall comply with IEC 60947-2, IEC 60947-6-2 or IEC 61009-1 or with the relevant parts of the IEC 60898 series or the IEC 60269 series.
  • Where the connecting point is a socket-outlet or a vehicle connector, it shall comply with IEC 60309-1 or IEC 62196-1 (where interchangeability is not required), or IEC 60309-2, IEC 62196-2, IEC 62196-3 or IEC TS 62196-4 (where interchangeability is required), or the national standard for socket-outlets, provided the rated current does not exceed 16 A.

Impact of EV charging on maximum power demand and equipment sizing

As stated in IEC 60364-7-722.311, "It shall be considered that in normal use, each single connecting point is used at its rated current or at the configured maximum charging current of the charging station. The means for configuration of the maximum charging current shall only be made by the use of a key or a tool and only be accessible to skilled or instructed persons."

The sizing of the circuit supplying one connecting point (mode 1 and 2) or one EV charging station (mode 3 and 4) should be done according to the maximum charging current (or a lower value, providing that configuring this value is not accessible to non-skilled persons).

Fig. EV22 – Examples of common sizing currents for Mode 1, 2, and 3
Characteristics Charging mode
Mode 1 & 2 Mode 3
Equipment for circuit sizing Standard socket outlet 3.7kW
single phase
7kW
single phase
11kW
three phases
22kW
three phases
Maximum current to consider
@230 / 400Vac
16A P+N 16A P+N 32A P+N 16A 3P+N 32A 3P+N

IEC 60364-7-722.311 also states that "Since all the connecting points of the installation can be used simultaneously, the diversity factor of the distribution circuit shall be taken as equal to 1 unless a load control is included in the EV supply equipment or installed upstream, or a combination of both."

The diversity factor to consider for several EV chargers in parallel is equal to 1 unless a Load Management System (LMS) is used to control these EV chargers.

The installation of an LMS to control the EVSE is therefore highly recommended: it prevents oversizing, optimizes the costs of the electrical infrastructure and reduces operating costs by avoiding power demand peaks. Refer to EV charging - electrical architectures for an example of an architecture with and without an LMS, illustrating the optimization gained on the electrical installation. Refer to EV charging - digital architectures for more details about the different variants of LMS, and the additional opportunities that are possible with cloud-based analytics ans supervision of EV charging. And check Smart charging perpectives for optimal EV integration for perspectives on smart charging.

Conductor arrangement and earthing systems

As stated in IEC 60364-7-722 (Clauses 314.01 and 312.2.1):

  • A dedicated circuit shall be provided for the transfer of energy from/to the electric vehicle.
  • In a TN earthing system, a circuit supplying a connecting point shall not include a PEN conductor

It should also be verified whether electric cars using the charging stations have limitations related to specific earthing systems: for example, certain cars cannot be connected in Mode 1, 2 and 3 in the IT earthing system (Example: Renault Zoe).

Regulations in certain countries may include additional requirements relating to earthing systems and PEN continuity monitoring. Example: case of TNC-TN-S (PME) network in the UK. To be compliant with BS 7671, in the case of upstream PEN break, a complementary protection based on voltage monitoring must be installed if there is no local earthing electrode.

Protection against electric shocks

EV charging applications increase the risk of electric shock, for several reasons:

  • Plugs: risk of discontinuity of Protective Earth conductor (PE).
  • Cable: risk of mechanical damage to cable insulation (crushing by rolling of vehicle tires, repeated operations…)
  • Electric car: risk of access to active parts of the charger (class 1) in the car as a result of destruction of basic protection (accidents, car maintenance etc.)
  • Wet or saltwater wet environments (snow on electric vehicle inlet, rain…)

To take these increased risks into account, IEC 60364-7-722 states that:

  • Additional protection with an RCD 30mA is mandatory
  • Protective measure "placing out of reach", according to IEC 60364-4-41 Annex B2, is not permitted
  • Special protective measures according to IEC 60364-4-41 Annex C are not permitted
  • Electrical separation for the supply of one item of current-using equipment is accepted as a protective measure with an isolating transformer complying with IEC 61558-2-4, and the voltage of the separated circuit shall not exceed 500 V. This is the commonly used solution for Mode 4.

Protection against electric shocks by automatic disconnection of the supply

The paragraphs below provide the detailed requirements of IEC 60364-7-722:2018 standard (based on Clauses 411.3.3, 531.2.101 and 531.2.1.1 etc.).

Each AC connecting point shall be individually protected by a residual current device (RCD) with a residual operating current rating that does not exceed 30 mA.

RCDs protecting each connecting point in accordance with 722.411.3.3 shall comply at least with the requirements of an RCD type A and shall have a rated residual operating current not exceeding 30 mA.

Where the EV charging station is equipped with a socket-outlet or vehicle connector that complies with IEC 62196 (all parts - "Plugs, socket-outlets, vehicle connectors and vehicle inlets – Conductive charging of electric vehicles"), protective measures against DC fault current shall be taken, except where provided by the EV charging station.

The appropriate measures, for each connection point, shall be as follows:

  • The use of an RCD type B, or
  • The use of an RCD type A (or F) in conjunction with a Residual Direct Current Detecting Device (RDC-DD) that complies with IEC 62955

RCDs shall comply with one of the following standards: IEC 61008-1, IEC 61009-1, IEC 60947-2 or IEC 62423.

RCDs shall disconnect all live conductors.

Fig. EV23 and EV24 below summarize these requirements.

Fig. EV23 – The two solutions for protection against electric shocks (EV charging stations, mode 3)
Fig. EV24 – Synthesis of IEC 60364-7-722 requirement for additional protection against electric shocks by automatic disconnection of the supply with RCD 30mA
Mode 1 & 2 Mode 3 Mode 4
RCD 30mA type A RCD 30mA type B, or

RCD 30mA type A + 6mA RDC-DD, or

RCD 30mA type F + 6mA RDC-DD

Not applicable

(no AC connecting point & electrical separation)

Notes:

  • the RCD or appropriate equipment that ensures disconnection of the supply in case of DC fault can be installed inside the EV charging station, in the upstream switchboard, or in both locations.
  • Specific RCD types as illustrated above are required because the AC/DC converter included in electric cars, and used to charge the battery, may generate DC leakage current.

What is the preferred option, RCD type B, or RCD type A/F + RDC-DD 6 mA?

The main criteria to compare these two solutions are the potential impact on other RCDs in the electrical installation (risk of blinding), and the expected continuity of service of EV charging, as shown in Fig. EV25.

Fig. EV25 – Comparison of RCD type B, and RCD type A + RDC-DD 6mA solutions
Comparison criteria Type of protection used in EV circuit
RCD type B RCD type A (or F)

+ RDC-DD 6 mA

Maximum number of EV connecting points downstream of a type A RCD to avoid the risk of blinding 0[a]

(not possible)

Maximum 1 EV connecting point[a]
Continuity of service of the EV charging points OK

DC leakage current leading to trip is [15 mA … 60 mA]

Not recommended

DC leakage current leading to trip is [3 mA … 6 mA]

In humid environments, or due to ageing of insulation, this leakage current is likely to increase up to 5 or 7 mA and may lead to nuisance tripping.

  1. ^ 1 2 These limitations are based on the DC max current acceptable by type A RCDs according to IEC 61008 / 61009 standards. Refer to next paragraph for more details on the risk of blinding and for solutions that minimize the impact and optimize the installation.

Important: these are the only two solutions that comply with the IEC 60364-7-722 standard for protection against electric shocks. Some EVSE manufacturers claim to offer "built-in protective devices" or "embedded protection". To find out more about the risks, and to select a safe charging solution, see the White Paper entitled Safety measures for charging electric vehicles

How to implement people protection throughout the installation despite the presence of loads that generate DC leakage currents

EV chargers include AC/DC converters, which may generate DC leakage current. This DC leakage current is let through by the EV circuit’s RCD protection (or RCD + RDC-DD), until it reaches the RCD/RDC-DD DC tripping value.

The maximum DC current that may flow through the EV circuit without tripping is:

  • 60 mA for 30 mA RCD type B (2*IΔn as per IEC 62423)
  • 6 mA for 30 mA RCD Type A (or F) + 6mA RDC-DD (as per IEC 62955)

Why this DC leakage current may be a problem for other RCDs of the installation

The other RCDs in the electrical installation may "see" this DC current, as shown in Fig. EV26:

  • The upstream RCDs will see 100% of the DC leakage current, whatever the earthing system (TN, TT)
  • The RCDs installed in parallel will only see a portion of this current, only for the TT earthing system, and only when a fault occurs in the circuit they protect. In the TN earthing system, the DC leakage current going through the type B RCD flows back through the PE conductor, and therefore cannot be seen by the RCDs in parallel.
Fig. EV26 – RCDs in series or in parallel are impacted by the DC leakage current that is let through by the type B RCD

RCDs other than type B are not designed to function correctly in the presence of DC leakage current, and may be "blinded" if this current is too high: their core will be pre-magnetized by this DC current, and may become insensitive to the AC fault current, e.g. the RCD will no longer trip in case of AC fault (potential hazardous situation). This is sometimes called "blindness", "blinding" or desensitization of the RCDs.

IEC standards define the (maximum) DC offset used to test the correct functioning of the different types of RCDs:

  • 10 mA for type F,
  • 6 mA for type A
  • and 0 mA for type AC.

That is to say that, considering characteristics of RCDs as defined by IEC standards:

  • RCDs type AC cannot be installed upstream of any EV charging station, regardless of the EV RCD option (type B, or type A + RDC-DD)
  • RCDs Type A or F can be installed upstream of a maximum of one EV charging station, and only if this EV charging station is protected by an RCD type A (or F) + 6mA RCD-DD

The RCD type A/F + 6mA RDC-DD solution has less impact (less blinging effect) when selecting other RCDs, nevertheless it is also very limited in practice, as shown in Fig. EV27.

Fig. EV27 – Maximum one EV station protected by RCD type A/F + 6mA RDC-DD can be installed downstream of RCDs type A and F

Recommendations to ensure correct functioning of RCDs in the installation

Some possible solutions to minimize the impact of EV circuits on other RCDs of the electrical installation:

  • Connect the EV charging circuits as high as possible in the electrical architecture, so that they are in parallel to other RCDs, to significantly reduce the risk of blinding
  • Use a TN system if possible, as there is no blinding effect on RCDs in parallel
  • For RCDs upstream of EV charging circuits, either
    • select type B RCDs, unless you have only 1 EV charger that uses type A + 6mA RDC-DD
    or
    • select non-type B RCDs which are designed to withstand DC current values beyond the specified values required by IEC standards, without impacting their AC protection performance. One example, with Schneider Electric product ranges: the Acti9 300mA type A RCDs can operate without blinding effect upstream up to 4 EV charging circuits protected by 30mA type B RCDs. For further information, consult the Schneider Electric Earth Fault Protection guide which includes selection tables and digital selectors.

You can also find more details in chapter F – RCDs selection in presence of DC earth leakage currents (also applicable to scenarios other than EV charging).

Examples of EV charging electrical diagrams

Below are two examples of electrical diagrams for EV charging circuits in mode 3, that are compliant with IEC 60364-7-722.

Fig. EV28 – Example of electrical diagram for one charging station in mode 3 (@home - residential application)
  • A dedicated circuit for EV charging, with 40A MCB overload protection
  • Protection against electric shocks with a 30mA RCD type B (a 30mA RCD type A/F + RDC-DD 6mA may also be used)
  • The upstream RCD is a type A RCD. This is only possible due to enhanced characteristics of this Schneider Electric RCD: no risk of blinding by the leakage current that is let through by the type B RCD
  • Also integrates Surge Protection Device (recommended)
Fig. EV29 – Example of electrical diagram for one charging station (mode 3) with 2 connecting points (commercial application, parking ...)
  • Each connecting point has its own dedicated circuit
  • Protection against electric shocks by 30mA RCD type B, one for each connecting point (30mA RCD type A/F + RDC-DD 6mA may also be used)
  • Overvoltage protection and RCDs type B may be installed in the charging station. In which case, the charging station could be powered from the switchboard with a single 63A circuit
  • iMNx : some country regulations may require emergency switching for EVSE in public areas
  • Surge protection not shown. May be added to the charging station or in upstream switchboard (depending on distance between switchboard and charging station)

Protection against transient overvoltages

The power surge generated by a lightning strike near an electricity network propagates into the network without undergoing any significant attenuation. As a result, the overvoltage likely to appear in a LV installation may exceed the acceptable levels for withstand voltage recommended by standards IEC 60664-1 and IEC 60364. The electric vehicle, being designed with an overvoltage category II according to IEC 17409, should therefore be protected against overvoltages that could exceed 2.5 kV.

As a consequence, IEC 60364-7-722 requires that EVSE installed in locations accessible to the public be protected against transient overvoltages. This is ensured by the use of a type 1 or type 2 surge protective device (SPD), complying with IEC 61643-11, installed in the switchboard supplying the electric vehicle or directly inside the EVSE, with a protection level Up ≤ 2.5 kV.

Surge protection by equipotential bonding

The first safeguard to put in place is a medium (conductor) that ensures equipotential bonding between all the conductive parts of the EV installation.

The aim is to bond all grounded conductors and metal parts so as to create equal potential at all points in the installed system.

Surge protection for indoor EVSE - without lightning protection system (LPS) - public access

The IEC 60364-7-722 requires protection against transient overvoltage for all locations with public access. The usual rules for selecting the SPDs can be applied (See chapter J - Overvoltage protection).

Fig. EV30 – Surge protection for indoor EVSE - without lightning protection system (LPS) - public access

When the building is not protected by a lightning protection system:

  • A type 2 SPD is required in the main low voltage switchboard (MLVS)
  • Each EVSE is supplied with a dedicated circuit.
  • An additional type 2 SPD is required in each EVSE, except if the distance from the main panel to the EVSE is less than 10m.
  • A type 3 SPD is also recommended for the Load Management System (LMS) as sensitive electronic equipment. This type 3 SPD has to be installed downstream a type 2 SPD (which is generally recommended or required in the switchboard where the LMS is installed).

Surge protection for indoor EVSE - installation using busway - without lightning protection system (LPS) - public access

This example is similar to the previous one, except that a busway (busbar trunking system) is used to distribute the energy to the EVSE.

Fig. EV31 – Surge protection for indoor EVSE - without lightning protection system (LPS) – installation using busway - public access

In this case, as shown in Fig. EV31:

  • A type 2 SPD is required in the main low voltage switchboard (MLVS)
  • EVSEs are supplied from the busway, and SPDs (if required) are installed inside busway tap-off boxes
  • An additional type 2 SPD is required in the first busway outgoer feeding an EVSE (as generally the distance to the MLVS is more than 10m). The following EVSEs are also protected by this SPD if they are less than 10m away
  • If this additional type 2 SPD has Up < 1.25kV (at I(8/20) = 5kA), there is no need to add any other SPD on the busway: all following EVSE are protected.
  • A type 3 SPD is also recommended for the Load Management System (LMS) as sensitive electronic equipment. This type 3 SPD has to be installed downstream a type 2 SPD (which is generally recommended or required in the switchboard where the LMS is installed).

Surge protection for indoor EVSE - with lightning protection system (LPS) - public access

Fig. EV32 – Surge protection for indoor EVSE - with lightning protection system (LPS) - public access

When the building is protected by a lightning protection system (LPS):

  • A type 1+2 SPD is required in the main low voltage switchboard (MLVS)
  • Each EVSE is supplied with a dedicated circuit.
  • An additional type 2 SPD is required in each EVSE, except if the distance from the main panel to the EVSE is less than 10m.
  • A type 3 SPD is also recommended for the Load Management System (LMS) as sensitive electronic equipment. This type 3 SPD has to be installed downstream a type 2 SPD (which is generally recommended or required in the switchboard where the LMS is installed).

Nota: if you use a busway for the distribution, apply the rules shown in the example without LTS, except for the SPD in the MLVS = use a Type 1+2 SPD and not a Type 2, because of the LPS.

Surge protection for outdoor EVSE - without lightning protection system (LPS) - public access

Fig. EV33 – Surge protection for outdoor EVSE - without lightning protection system (LPS) - public access

In this example:

  • A type 2 SPD is required in the main low voltage switchboard (MLVS)
  • An additional type 2 SPD is required in the sub panel (distance generally >10m to the MLVS)

In addition:

When the EVSE is linked with the building structure:

  • use the building’s equipotential network
  • if the EVSE is less than 10m from the sub panel, or if the type 2 SPD installed in the sub panel has Up < 1.25kV (at I(8/20) = 5kA), there is no need for additional SPDs in the EVSE

When the EVSE is installed in a parking area, and supplied with an underground electrical line:

  • each EVSE shall be equipped with an earthing rod.
  • each EVSE shall be connected to an equipotential network. This network must also be connected to the building’s equipotential network.
  • install a type 2 SPD in each EVSE

A type 3 SPD is also recommended for the Load Management System (LMS) as sensitive electronic equipment. This type 3 SPD has to be installed downstream a type 2 SPD (which is generally recommended or required in the switchboard where the LMS is installed).

Surge protection for outdoor EVSE - with lightning protection system (LPS) - public access

Fig. EV34 – Surge protection for outdoor EVSE - with lightning protection system (LPS) - public access

The main building is equipped with a lightning rod (lightning protection system) to protect the building.

In this case:

  • A type 1 SPD is required in the main low voltage switchboard (MLVS)
  • An additional type 2 SPD is required in the sub panel (distance generally >10m to the MLVS)

In addition:

When the EVSE is linked with the building structure:

  • use the building’s equipotential network
  • if the EVSE is less than 10m from the sub panel, or if the type 2 SPD installed in the sub panel has Up < 1.25kV (at I(8/20) = 5kA), there is no need to add additional SPDs in the EVSE

When the EVSE is installed in a parking area, and supplied with an underground electrical line:

  • each EVSE shall be equipped with an earthing rod.
  • each EVSE shall be connected to an equipotential network. This network must also be connected to the building’s equipotential network.
  • install a type 1+2 SPD in each EVSE

A type 3 SPD is also recommended for the Load Management System (LMS) as sensitive electronic equipment. This type 3 SPD has to be installed downstream a type 2 SPD (which is generally recommended or required in the switchboard where the LMS is installed).

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