Introduction
Given that promoting zero carbon emissions from vehicles is widely adopted around the world as one of the key strategies to achieve carbon neutrality, the HKSAR Government announced the Hong Kong Roadmap on Popularisation of Electric Vehicles in 2021. As part of Hong Kong’s Climate Action Plan 2050, the Roadmap sets out the long-term policy objectives and plans to promote the adoption of electric vehicles (EVs) and their associated supporting facilities in Hong Kong, with the aim of attaining zero vehicular emissions before 2050.
In recent years, Hong Kong has seen a sharp rise in the number of EVs and the percentage of electric private cars among newly registered private cars. More and extensive charging facilities are therefore required for the establishment of a charging network to keep the momentum going and support the popularisation of EVs.
To tie in with the HKSAR Government’s efforts to promote the wider use of EVs and their supporting facilities, the Electrical and Mechanical Services Department (EMSD) has devised a new code on charging facilities for EVs (namely, Code 26S) and incorporated it into the latest edition of the Code of Practice for the Electricity (Wiring) Regulations as shown in Figure 1, which has become fully effective since 31 December 2021. Code 26S sets out the particular requirements for the installation of EV charging facilities, including the circuit arrangements for the charging facilities, classification of charging modes, selection and erection of the charging equipment, protection for safety and allowances for diversity.
In addition, to ensure electrical safety, the EMSD published the Guidance Note on Fault Protection for Direct Current Electric Vehicle Charging Facilities (Guidance Note) in October 2022 as shown in Figure 2, to provide detailed guidelines on how to meet the requirements for fault protection of direct current (DC) EV charging facilities, so as to facilitate the quick and safe installation of such facilities. Salient points of Code 26S and the Guidance Note as well as other related matters are set out in the ensuing paragraphs.
Figure 1: Code of Practice for the Electricity (Wiring) Regulations (2020 Edition)
Figure 2: Guidance Note on Fault Protection for Direct Current Electric Vehicle Charging Facilities
Fault protection requirements of respective charging modes
Except for circuits using the protective measure of electrical separation, each charging point shall be protected by its own residual current device (RCD) of at least Type A. In addition, except where provided by the EV charging equipment, protective measures against DC fault current shall be taken for each charging point with a socket outlet or connector complying with the IEC 62196 series. Specific fault protection requirements for respective modes of charging are deliberated as below:
Mode 1 & Mode 2 charging
For Mode 1 charging and Mode 2 charging, except for circuits using the protective measure of electrical separation, each charging point shall be protected by its own RCD of at least Type A.
Mode 3 charging
The socket outlet or connector for Mode 3 charging shall comply with the IEC 62196 series or its equivalents. Therefore, when EV charging facilities for Mode 3 charging are to be installed, appropriate protective measures against DC fault current shall be taken for each connection point as follows:
• An RCD of Type B shall be installed on the supply circuit of the charging point; or
• An RCD of Type A shall be installed on the supply circuit of the charging point and protective measures against DC fault current, such as a built-in residual direct current detecting device (RDC-DD) complying with the IEC 62955 standard, shall be provided by the EV charging equipment to disconnect the supply in case of DC fault current above 6 mA.
Mode 4 charging
Generally speaking, for a DC EV charging facility as illustrated in Figure 3, the EV is connected to the alternating current (AC) supply network through an off-board charger permanently connected to the AC supply, with the DC supplied to the EV via a charging cable that is attached to the charger and fitted with a connector in compliance with the IEC 62196 series.
Figure 3: Typical arrangement of a DC EV charging facility for Mode 4 charging
DC EV chargers in compliance with IEC 61851-23:2014 can be classified into two categories, namely (i) isolated DC EV charger; and (ii) non-isolated DC EV charger. The fault protection requirements for each of the above are set out as follows:
(i) Isolated DC EV charger
As the DC circuit on the output side of the charger is electrically separated from the AC circuit on the power system side, and as this electrical separation can be considered as a means of protective measure, protection by an RCD is optional.
(ii) Non-isolated DC EV charger
As the DC circuit on the output side of the charger is not electrically separated from the AC circuit on the power system side, such charger shall be protected by an RCD of at least Type A.
In addition, DC EV chargers in compliance with IEC 61851-23:2014 are required to be compatible with RCDs of Type A to be installed as specified in Clause 7.6 of the standard (namely, any RCD of Type A to be installed on the AC supply circuit upstream to the chargers shall be able to be used together with the charger and function safely as intended). As such, an RCD of Type B is not required for a DC EV charger in compliance with IEC 61851-23:2014.
Method for checking the fault protection measures
Tests can be conducted to verify that the installed protective device is functioning in accordance with international standards. The EV charger's type test report could also be checked to ascertain that appropriate fault protection measure is in place.
Proper tools and instruments for conducting the test
In order to ensure that the RCDs or protective measures against fault current of the EV charging installation are functioning properly, registered electrical workers should use appropriate testing equipment to simulate a prospective earth fault to verify the effectiveness of the protective measure. Some examples of suitable testing equipment may include the following:
(i) An RCD tester that is suitable for testing an RCD of Type A, RCD of Type B and an RDC-DD (commonly known as an RCD of EV type on the market), and that is capable of applying testing current for leakage to simulate respective earth faults.
(ii) A test adapter that can be used with an EV charging socket to simulate the connection of the EV to a charging point to be tested and put the charging equipment into a charging state, while the test adapter should also be equipped with a general electrical socket outlet or connection port for connection to an RCD tester to conduct the test.
Tripping characteristics of the protective measures against fault current
• For RCDs of Type A having a rated residual operating current not less than 30 mA, in compliance with IEC 61008, if the half wave pulsating residual current reaches or exceeds 1.4 times the rated residual operating, the above RCDs should trip and cut off the current in less than 0.3 seconds.
• For RCDs of Type B complying with IEC 62423, if the DC leakage current reaches or exceeds twice the rated residual operating current, the above RCDs should trip and cut off the current in less than 0.3 seconds.
• For RDC-DDs complying with IEC 62955, if the DC leakage current reaches or exceeds 6 mA, the internal or external protective devices of the above RDC-DDs should trip and cut off the current in less than ten seconds. If the DC leakage current reaches or exceeds 60 mA, the protective devices should trip and cut off the current in less than 0.3 seconds.
Compliance checking of Mode 4 EV chargers
Besides reviewing the test certificate to ensure the DC EV charger conform to IEC 61851-23:2014, registered electrical workers should identify the classification of DC EV chargers and check the protection against electric shock in order to determine the respective fault protection measures to be applied. This can be achieved by checking the DC EV charger’s type test reports and taking into account the applicable clauses of IEC 61851-23:2014, which may include but are not limited to the following:
• Clause 6.101 on the classification of DC EV chargers;
• Clause 7 on protection against electric shock; and
• Annexes AA.3.1, BB.2 or CC.4.1 on the requirements for different types of isolated DC EV chargers for protection against electric shock, etc.
For details on how to meet the requirements for fault protection of DC EV charging facilities, please refer to the Guidance Notes here on the EMSD’s website or scan the QR code below.
Conclusion
Hong Kong’s attainment of carbon neutrality before 2050 relies heavily on the wider use of EVs and the development of a robust charging network to support their operation. To ensure the safe installation of EV charging facilities, Code 26S has been introduced, stating the specific technical requirements. To provide further practical guidance on the safe installation of DC EV charging facilities, the Guidance Note has also been published. We are committed to ensuring electrical safety and striving for zero vehicular emissions in partnership with the industry. With the publication of the above and the full support of the industry, it is hoped that more EV charging facilities will be installed properly to facilitate the wider adoption of EVs, which will in turn enable Hong Kong to advance towards carbon neutrality in a quicker pace.