Open combined protective and neutral (PEN) conductor detection devices (OPDDS), IET 01

The IET, working with industry stakeholders, has prepared a specification for the operation of electric vehicle (EV) charging equipment when particular faults occur. This specification is to be known as IET 01, Open combined protective and neutral (PEN) conductor detection devices (OPDDs) – OPDDs for use in electric vehicle charging applications for household and similar installations.

IET 01 addresses the specification for devices that detect the symptoms of faults that can occur on the distribution network cables external to the consumer’s electrical installation, i.e. those cables owned and operated by electricity distribution companies and which are beyond the control of the installation owner or the operator of the charging equipment. These particular faults on the distribution network cables can lead to dangerous voltages appearing between the metallic shell of an electric vehicle (EV), whilst it is on charge, and Earth; by ‘Earth’ it is meant the ground that you walk on.

To some extent, the faults seen on the distribution network are specific to countries that use TN-C-S earthing arrangements for the public supply. In the UK, the low voltage electricity supply is generally distributed to our homes and businesses in a TN-C-S arrangement; C indicates that there is a ‘combined’ conductor in the network that performs both the neutral and protective functions.

This is the ‘PEN’ conductor, an abbreviation for ‘Protective Earth and Neutral’. If this conductor is severed, due, for example, to roadworks or even corrosion, a dangerous voltage can appear between Earth and any metalwork connected to the protective conductors of the electrical installation.

Work on IET 01 has been fuelled by changes over the years to BS 7671, The IET Wiring Regulations, 18th Edition; the current version being BS7671:2018+A2:2022+A3:2024. BS 7671 requires EV charging equipment to, amongst other things, cease charging and completely isolate the vehicle from the charging equipment when an open PEN conductor fault occurs on the electricity distribution network.

Most manufacturers of EV charging equipment can provide such functionality but not all manufacturers do it in the same way. For example, some manufacturers add in other functionality that may seem helpful but it is not always clear whether it is necessary. Others require the installation of an earth electrode to enable the measurement of the electrical potential difference to Earth. It is challenging for electrical installers to choose the right chargepoint for the right circumstances and differing external influences faced at the chosen point of installation.

In any event, BS 7671 is an installation standard and should not include operational parameters for products; it does so because there has previously been no alternative.

It was clear that there is not a standard way of working for EV charging equipment with these considerations in mind. Yes, a product standard exists (BS EN 61851-1) but it does not specify how charging equipment must behave when an open PEN fault occurs on the TN-C-S distribution network.

With the initial work on IET 01 now complete, the intention is three-fold.

Firstly, that IET 01 may be considered for citation within BS 7671 as the specification to which EV charging equipment should conform, thus, enabling the removal of overlapping or potentially conflicting requirements from BS 7671.   

Secondly, manufacturers adopt IET 01 and make their EV charging equipment conform with this specification and that the equipment is labelled accordingly. Labelling helps installers to identify which type of protection mechanism is offered by an OPDD, and how to install the product safely. The types of protection mechanism offered by IET 01 address grid-stability concerns due to unwanted operation from small rises, dips and interruptions that sometimes occur in the supply voltage. IET 01 also provides options for manufacturers to produce OPDDs that are intended to be compatible with vehicle-to-grid and vehicle-to-home applications.

Thirdly, that IET 01 continues to be developed, expanded and updated in response to industry needs as they arise and that, overall, it contributes to the setting of standards for electrical safety.

The IET believes achieving these goals for IET 01 will make it easier for designers and electrical installers to choose a suitable product to meet individual circumstances and requirements. This will provide efficiencies for the installer and improve safety for operators and users of EV charging equipment and for members of the public.