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RCDs for electric vehicle supply equipment (EVSE)

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The installation of EVSE is becoming common place but installers still have many questions on the subject. This article focuses on RCD protection for Mode 3 charging of electric vehicles (EVs) and looks at the requirements of BS 7671:2018+A2:2022. 

What are the RCD requirements for the different charging modes?

Mode 1 and Mode 2 charging utilizes BS 1363 socket-outlets and a Type A RCD is required at the socket-outlet or for the circuit, installed within the consumer unit. Mode 3 charging is provided by a dedicated circuit, typically single-phase 7 kW or three-phase 22 kW. This is the most common type of EV charger installed in domestic (household) premises. The RCD requirements are covered in detail in this article.

Mode 4 charging is provided by a dedicated AC supply circuit to the EVSE. The EVSE uses switch mode power supplies (SMPS) to convert the AC to DC which is used on the output circuit. Mode 4 charging is typically used for publicly available fast charging 50 kW to 350 kW. Requirements for the selection and erection of RCDs in the case of supplies using DC vehicle connectors according to the BS EN 62196 series are under consideration, Note 2 to Regulation 722.531.3.101 of BS 7671:2018+A2:2022 refers.  For Mode 4 charging, RCDs may be required for the AC supply circuit, for example, if it forms part of a TT system or where disconnection times cannot be met using circuit-breakers. RCDs, however, are not required on the DC side as electric shock protection is provided by the manufacturer of the EVSE.

Figure 1: Mode 4 DC fast charger

What are the standards and regulations for EVSE?

In order for electrical equipment to be sold in the UK, the electrical equipment must conform to the Electrical Equipment (Safety) Regulations 2016 and the Electromagnetic Compatibility Regulations 2016 (as amended). The Electric Vehicles (Smart Charge Points) Regulations 2021 also apply to Mode 3 EVSE. These are statutory regulations and must be adhered to by manufacturers of EVSE.

Compliance with standards is voluntary but it can help to demonstrate conformity with the relevant legislation. This is known as presumption of conformity.

The series of standards for the design and performance requirements for EV conductive charging equipment is the BS EN IEC 61851/BS EN 61851 series.

Section 722 of BS 7671:2018+A2:2022 provides requirements for the installation of EVSE, in addition to the general requirements of Parts 1 to 6.

What are the RCD requirements in BS 7671 for EVSE?

Regulation 722.531.3.101 of BS 7671:2018+A2:2022 states that unless the circuit is supplied using the protective measure of electrical separation, each charging point incorporating a socket-outlet or vehicle connector complying with the BS EN 62196 series is to be protected individually by an RCD of Type A, Type F or Type B and having a rated residual operating current not exceeding 30 mA. The RCD is also required to disconnect all live conductors.

The definition of an electric vehicle charging point in BS 7671:2018+A2:2022 is “the point where the electric vehicle is connected to the fixed installation”. This means that the requirement for RCD protection applies to the socket-outlet or connector and not the circuit supplying the EVSE. A note clarifies that the point is the socket-outlet supplying the electric vehicle, or a connector where the charging cable is not part of the EVSE.

There may be other reasons why RCD protection is required to protect the final circuit, such as where the installation forms part of a TT earthing system, where cables are buried in walls at a depth of less than 50 mm or where a high earth fault loop impedance requires an RCD in order to achieve fault protection.

What type of RCD is required?

EVSEs are likely to produce DC residual current during operation. This is due to the design of the electronic equipment for the charging circuit within the EVSE. The DC residual current will be superimposed on the AC waveform which will affect the operation of RCDs. The type of RCD required depends on the protection against DC residual current installed in the EVSE.

Where no protection against DC residual current is provided in the EVSE, Regulation 722.531.3.101 of BS 7671:2018+A2:2022 requires a Type B RCD to be installed. Where protection against DC residual current is provided in the EVSE, a Type A or Type F RCD can be used. This is typically provided by a Type A RCD in conjunction with a residual direct current detecting device (RDC-DD), complying with BS IEC 62955 as appropriate to the nature of the residual and superimposed currents and recommendation of the manufacturer of the charging equipment.

BS EN 62955:2018 provides requirements for RDC-DDs to be used for Mode 3 charging of electric vehicles. RDC-DDs are detection devices for DC residual current which do not incorporate a mechanical switching function. Switching is provided by an external device, such as a contactor which is actioned by the RDC-DD.

It is also important to consider any RCDs installed upstream as they could also be blinded by DC residual current. The hierarchy of RCDs with respect to DC residual current should be observed. For example, a Type AC RCD should not be installed upstream of a Type A RCD. The BEAMA GUIDE - selection and application of RCDs provides useful information. There is also a BEAMA guide specific to EV charging installations, BEAMA guide - RCD selection for protection of electric vehicle charging installations.

As with all electrical equipment, account should be taken of the EVSE manufacturer’s instructions.

Figure 2: Type B RCD conforming to BS EN 61008

Can I use an EVSE with an integrated RCD?

Some manufacturers state that EVSE contains integrated RCDs.

A question often asked is “if additional protection by an RCD is integrated within the EVSE could RCD protection be omitted in the dedicated/final circuit?”

After all, the requirement for RCD protection is to be provided for the socket-outlet and not the final circuit.  

BS 7671:2018+A2:2022 does not dictate the location for the RCD. Regulation 722.531.3.101 of BS 7671:2018+A2:2022 states that “except where provided by the EV charging equipment”, protection against DC fault current shall be provided by a Type B RCD or a Type A or Type F in conjunction with an RDC-DD. This is further clarified in Note 3 to Regulation 722.531.3.101. So, it is clear that it is acceptable to locate an RCD within the EVSE.

The type of RCD, however, is specified in Regulation 722.531.3.101 of BS 7671:2018+A2:2022. RCDs are required to comply with one of the following standards, BS EN 61008-1, BS EN 61009-1, BS EN 60947-2 or BS EN 62423. If the RCD included in the EVSE complies with one of these standards, then it could be used for additional protection for the electric vehicle charging point without the need for additional RCD protection upstream.

Often RCDs built in to EVSE, i.e. integrated into the printed circuit board (PCB), do not fully conform to any of the standards required by Regulation 722.531.3.101 of BS 7671:2018+A2:2022 or Clause 8.5 of BS EN IEC 61851-1:2019.

What is an ‘integrated’ RCD?

In simple terms, an ‘integrated’ RCD is an electronic device controlled by an algorithm programmed to operate in a similar way to how a traditional RCD operates according to the relevant product standards.

Some EVSE incorporates a residual direct current protective device (RDC-PD), a protective device with integrated AC, pulsating DC and 6 mA DC detection, evaluation and mechanical switching in one unit. The requirements for RDC-PDs are provided in Annex O (normative) of BS IEC 62955:2018. With the exception of a couple of clauses modified by BS IEC 62955, RDC-PDs must conform to all the requirements of either IEC 61008 or IEC 61009.

An RDC-DD/RDC-PD is not one of those devices cited in Regulation 722.531.3.101, which leaves the installer in a difficult position. BS 7671 and BS EN IEC 61851 mandate that RCDs shall comply with one of the following standards: BS EN 61008-1, BS EN 61009-1, BS EN 60947-2 or BS EN 62423.

Figure 3: Mode 3 EV charger with integrated electronic RCD

Can I install equipment which does not comply with any British Standards?

Yes, but any intended departure requires special consideration by the designer of the installation in consultation with the client and other interested parties. It is important to note that the resulting degree of safety of the installation shall be not less than that obtained by compliance with BS 7671:2018+A2:2022, Regulation 120.3 refers. Any intended departures along with the justification must be recorded on the electrical certification.

Regulation 122.1.2 states that where there are no applicable standards, the item of equipment concerned shall be selected by a special agreement between the person specifying the installation and the installer. This route requires careful consideration as it could result in liabilities at a future date.

Regulation 133.5 provides requirements for new materials and inventions, and Regulation 133.1.3 provides requirements for equipment which does not comply with any British or Harmonized Standard or used outside the scope of its standard. Again, the resulting degree of safety of the installation shall be not less than that obtained by compliance with the BS 7671:2018+A2:2022, and the chances of the EVSE manufacturer putting this clearly in writing is unlikely.

Regulation 722.411.4.1 of BS 7671:2018+A2:2022 recognizes that equipment can be used which is not covered by a British or Harmonized Standard, in this case, open PEN detection devices. It is required that the equipment meets the requirements of statutory legislation, the Electrical Equipment (Safety) Regulations 2016 (as amended), the Electromagnetic Compatibility Regulations 2016 (as amended) and other relevant legislation, and the equipment has either a CE, UKCA or UKNI mark and a Declaration of Conformity (DOC). The DOC is to be appended to the certification for initial verification and where this is satisfied, it is not considered to be a departure from BS 7671:2018+A2:2022.

What is a declaration of conformity?

When installing any item of electrical equipment, it is important the manufacturers supply a DOC. A DOC is a mandatory document provided by manufacturers to declare their products comply with the law.

The CE, UKCA or UKNI mark accompanied by the DOC document confirms that the manufacturer takes full responsibility for the products compliance with the applicable laws. The DOC is usually available on the manufacturer’s website or available on request. The DOC will specify the relevant regulations and standards to which the product conforms.  

What if the manufacturer states an RCD is not required?

Be wary of claims by manufacturers that an external RCD is not required for EVSE. Some manufacturers of EVSE declare on their website that the equipment does feature an integrated RCD which operates ‘similar’ to a traditional RCD complying with BS EN 61008 or BS EN 61009. If the RCD, however, is integrated into the circuit board, it will not conform to the RCD product standards.

When inspectors of competent person schemes carry out their audits, they will be looking for compliance with BS 7671 and will expect to see an external RCD installed in such circumstances. 

Sweden bans EV chargers with integrated RCDs

Swedish authorities have recently placed a sales ban on a manufacturer of electric vehicle charge points. One of the issues raised is regarding the use of integrated electronic RCDs. The manufacturer has provided a robust response and maintains that their products are safe and it is a matter of correct documentation.

Summary

Regulation 722.531.3.101 of BS 7671:2018+A2:2022 requires RCDs to protect the charging point, i.e. the socket-outlet or connector and not, necessarily, the circuit supplying it.

The RCD can be installed at the distribution board or within the EVSE. RCD functionality built into circuit boards does not conform to the relevant product standards required by BS 7671:2018+A2:2022 or BS EN IEC 61851-1:2019.

RCDs shall disconnect all live conductors and comply with one of the following standards, BS EN 61008-1, BS EN 61009-1, BS EN 60947-2 or BS EN 62423.

For Mode 3 charging, a Type A or Type F RCD is required where protection against DC residual current in the form of an RDC-DD is provided within the EVSE.

Where the EVSE does not incorporate such protection, a Type B RCD is required. When installing EVSE, account should be taken of manufacturer’s instructions.

Further reading

Acknowledgements

  • Bob Cairney (SELECT)
  • Craig O’Neill (IET)
  • Curtis Jones (ECA)
  • Darren Crannis (ECA)
  • Frank Bertie (NAPIT)
  • Gary Gundry
  • Gary Parker (ECA)
  • Joe Cannon (IET Volunteer)
  • John Peckham (IET Volunteer)
  • Leon Markwell (IET)
  •  Mark Coles (IET)
  • Peter Monfort (Arena training)
  • Stuart McKelvie (SELECT)