Richard Winter, Director at matt:e, discusses why the company’s patented O-PEN device offers the safest form of PEN fault protection for three-phase infrastructures.
The installation of EV charging equipment is a complex matter and requires specialist knowledge, particularly of earthing systems that are covered in section 722 of BS 7671.
TN-C-S (PME) is the most common form of earthing provided at new installs, and utilises a single conductor for the neutral and earthing functions (PEN) with an earth terminal derived from the neutral cable.
The danger arises if there is an open PEN conductor within the network; this can lead to an electric shock if any metallic parts, including the EV or charging equipment, are touched by a person in simultaneous contact with general mass of Earth.
Because of this risk BS 7671 doesn’t permit the use of a PME earthing system for the protective conductor contact of a charging point located outdoors or that might reasonably be expected to be used to charge a vehicle located outdoors. It shouldn’t be used or connected into EV chargepoint equipment unless some specific methods are followed, which are covered in section 722.
The patented O-PEN system from matt:e is able to detect open PEN faults on three-phase PME infrastructures, facilitating compliance with BS 7671: 2018 Amendment 2: 2022 Regulation 722.411.4.1 (iii), whereby a star point is derived from the three-phase supply creating a ‘zero’ reference point used to measure against the supply neutral. If 70 volts between these two points is measured, all line conductors (including CPC) are disconnected to isolate the load.
Use an O-PEN device for three phases
As single-phase devices aren’t 100% reliable and because of the risk that they may not detect all faults on the supply network, matt:e always recommends the use of the O-PEN device when the three-phases of the supply are available.
One benefit of using a matt:e EV connection centre compared to using traditional earth rods is that it isn’t seasonal – earth rod resistance can and does change depending on the season, so an EV install may be compliant in the winter but non-compliant in the summer. A further benefit in using the matt:e EV connection centres is that they negate the need for difficult to achieve separation distances between an earth rod and any services connected to the TN-C-S earthing system.
Isolation of the EV is extremely important in single and three-phase installations, after all it is pointless detecting the fault if you don’t provide safe isolation. Compliant isolation is covered by BS 7671 Regulation 522.214.171.124 (ii) and states a ‘multipole, linked switching device’.
Therefore a 3-pole device is used in a single-phase installation and 5-pole in a three-phase installation and these must be suitable for isolating ‘onload’. Suitable devices are listed in BS 7671 table 537.4 and with the on-load isolation symbol shown in NOTE 1.
Centres of excellence
The UK manufactured matt:e range of EV connection centres with O-PEN technology offer real time measurement (so no guess work or second events to trip), and all units provide onload isolation in accordance with BS 7671 Regulation 5126.96.36.199 (ii) and table 537.
Use of the connection centres helps to standardise installations, ensuring there’s no more scanning for buried services and that civil works are minimised. A safer earth connection is provided (as the unit is connected directly to the PME supply) and users can guarantee that the earth resistance values are met and maintained all year round.
To watch a demonstration video of the O-PEN device, click here