NAPIT Technical Events Manager, Paul Chaffers, gives an overview of the Amendment to IET 18th Edition Wiring Regulations (BS 7671:2018) related to EV charging.
Since the announcement of Amendment 1 to BS 7671 which was published in February of this year, BS 7671:2018 Amendment 1:2020, is available and free-to-view on the IET website as a stand-alone update to Section 722 for Electric Vehicle (EV) charging installations.
This included a change to the introduction of Regulations where ALL EV changing points designed and installed after 31st July must comply with Amendment 1 requirements. Therefore these changes are now in force.
The decision to release this Amendment follows advances in technology enabling a more practical solution for EV charging installations. One of the main changes is with regards to Protective Multiple Earthing (PME) systems. Contractors already familiar with EV charging installations will be aware of the restrictions on the use of PME earthing facilities used outside for the protective conductor contact of a charging point.
Regulation 722.411.4.1 introduces two new indents – (iv) and (v) – which provides alternative solutions for charging installations using PME earthing systems. The existing installation options (i), (ii) and (iii) have been slightly modified and are still available for use. However, many contractors found these conditions hard to meet, as summarised here.
Summary of existing installation methods (i), (ii) and (iii)
(i) The first option concerns charging points forming part of a three-phase installation also supplying non-vehicle charging loads. The maximum voltage between the MET and Earth in the event of an open-circuit fault in the Protective and Neutral Conductor – combined (PEN) conductor of the low voltage network supplying the installation does not exceed 70 V rms.
This option relies on the system being balanced, which in theory would be hard to achieve.
(ii) The second option requires the installation MET to be connected to an auxiliary earth electrode. The resistance of the earth electrode to Earth, shall be such that the maximum voltage between the main earthing terminal of the installation and Earth in the event of an open-circuit fault in the PEN conductor of the low voltage network supplying the installation does not exceed 70 V rms.
The conditions for this option are very hard to meet, due to the very low resistance needed to achieve the 70 V rms touch voltage threshold.
(iii) The third option concerns the use of a device which disconnects the charging point from the live conductors of the supply and from protective Earth (in accordance with Regulation 5126.96.36.199(ii)) within 5 seconds in the event of the voltage between the circuit protective conductor and Earth exceeding 70 V rms.
The device need not operate if the voltage exceeds 70 V rms for less than four seconds. The device shall provide isolation, with closing or resetting of the device possible only if the voltage between the circuit protective conductor and Earth does not exceed 70 V rms.
This method requires a suitable reference to Earth due to the fact that during a PEN failure in the supply network, the neutral of a TN-C-S (PME) supply is no longer considered to be reliably connected to Earth, and therefore measurement of voltage will need to be between the circuit protective conductor and a suitable measurement earth electrode.
Annex A722 provides further guidance, and one notable requirement is for the positioning of any measurement electrodes to be located at a sufficient distance from other earth electrodes, and/or other buried exposed-conductive-parts, and/or extraneous conductive-parts connected to the PME earthing terminal to reduce transfer of earth potential rise on the PME system during a PEN failure.
To avoid having to meet the onerous conditions listed above, most contractors opted for using a TT earthing arrangement, as illustrated in Fig 1.
However, Amendment 1 suggests caution with this approach in a new note (Note 6), which states that creating a TT earthing system for charging equipment, or the whole installation, as an alternative to using a PME earthing facility, may not be an appropriate solution due to the inability to provide sufficient separation from buried metalwork connected to the supply PEN conductor.
New installation methods (iv) and (v), providing alternative solutions
(iv) This new option concerns single-phase installations only, where protection against electric shock is provided by a device which electrically disconnects the vehicle from the live conductors of the supply and from protective Earth, in accordance with Regulation 5188.8.131.52(ii) within 5 seconds.
Characteristics of losing the PEN conductor in a single-phase installation include hazardous touch voltages being present on exposed-conductive-parts, as well as fluctuating voltage.
Therefore, the device must monitor the utilisation voltage at the charging point between the line and neutral conductors, and shall provide isolation should the voltage parameters of 253 V rms or less than 207 V rms be reached.
(v) Indent (v) permits the use of an alternative device to those in (iii) or (iv) for protection against electric shock. It must not result in a lesser degree of safety than using (iii) or (iv).
The device (or means of functionality) shall operate by electrically disconnecting the vehicle from the live conductors of the supply and from protective earth in accordance with Regulation 5184.108.40.206(ii). It shall provide isolation and be selected in accordance with Table 537.4.
This option allows manufacturers to design and construct charging equipment with no restrictions on the design, providing the fundamental requirements for isolation can be achieved under (loss of PEN) fault conditions.
Included with the requirements of indent (iii), (iv) and (v) is a statement that equivalent means of functionality could be included within the charging equipment.
However, BS 7671 does not deal with the safety requirements for the construction of electrical equipment and therefore further information is provided in a new note (Note 5) accompanying Regulation 722.411.4.1.
Regulation 5220.127.116.11 permits inserting a switching device in the protective conductor under certain conditions. Indent (ii) of Regulation 518.104.22.168 requires multipole, linked switching in which the protective conductor circuit is not interrupted before the live conductors, and is re-established not later than when the live conductors are reconnected.
The device used for isolation in conditions (iii), (iv) and (v) must be selected in accordance with Table 537.4 of BS 7671, which provides guidance on the selection of protective, isolation and switching devices.
A further requirement is that where a device is provided for the purposes of (iii), (iv) and (v) the protective conductors and exposed-conductive-parts downstream of the protective device shall have no connection to:
(a) any protective conductors or exposed-conductive-parts of any circuit not protected by the
same protective device, or;
(b) any extraneous-conductive-parts.
New RCD references
The requirements introduced with the release of the 18th Edition placed more importance on the correct selection of RCD type. Regulation 531.3.3 which describes RCDs in respect of their behaviour when exposed to DC components and frequencies.
Section 722 previously required that unless using the protective measure of electrical separation, each charging point shall be protected by its own 30 mA RCD of at least Type A and, for certain conditions, Type B RCDs were required.
Amendment 1 introduces further RCD terminology, the Type F RCD and the introduction of RDC-DD. The requirements are as follows:
Except where provided by the EV charging equipment, protection against DC fault currents shall be provided by:
(i) an RCD Type B, or;
(ii) an RCD Type A or Type F 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.
Table 1 provides RCD information with operating restrictions and marking symbols.
Maximum demand and diversity
Previously 722.311 required a dedicated circuit for the connection of electric vehicles with no allowances for diversity, meaning that unless the installation had enough spare capacity for the rated current of the charging point, the installation could not go ahead.
Amendment 1 removes this requirement and introduces 722.311.201, which permits load curtailment, including load reduction or disconnection. It states that this can be applied either automatically or manually and may be taken into account when determining maximum demand of the installation or part thereof.
NAPIT welcomes the new updated Section 722 as this will make installing charging points quicker and easier, helping to reduce the cost of installations for both installers and customers.
The new requirements for assessing maximum demand with the use of load curtailment will help remove further installation barriers. Potential hazards associated with driving earth electrodes into the ground will now be reduced and there will be no concerns regarding simultaneous contact of two different earthing systems.
By selecting EV charging equipment where the manufacturer has a declaration of conformity stating that their equipment meets the requirements of Regulation 722.411.4.1 (iii), (iv) or (v), no further consideration is needed regarding the use of a PME earthing facility.
It is recommended that the declaration of conformity is retained with the design records for future scrutiny.
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