WHAT IS BUILT-IN PEN PROTECTION?
Built-in PEN Protection Explained
Many homes in the UK have a PME (Protective Multiple Earthing) supply meaning that the building’s earth connection is connected to the neutral conductor (Protective Earthed Neutral (PEN) conductor) at the incoming supply point. This provides a reliable way of providing an earth to a property, however, if there was ever to be an open circuit fault on the PEN conductor, there is a possibility of potential shock hazards which RCDs cannot detect.
Typically, the combined PEN conductor is earthed multiple times on its route back to the substation transformer, providing a low impedance path between neutral and earth and allowing RCDs to operate reliably within the property. In the event that the PEN conductor is broken, dangerous voltages can appear on all conductive parts of the installation. During this fault, there is no potential difference between conductors and the risk is low, however, any contact with a conductive part could provide a current path to true earth and cause an electric shock.
VEVA continuously monitors the incoming supply to detect problems with the PEN conductor. If problems are detected, VEVA automatically disconnects the supply to the output of the charger, ensuring it is isolated, and meaning there is no risk of electric shock. The protection provided is compliant with regulation 722.411.4.1(v) of BS7671:2018-amd1: 2020 meaning when directly connected to a TN-C-S (PME) earthing system, an earth electrode is not required.
Why it this important in an EV charger?
As discussed above, in the event of a broken PEN conductor, dangerous voltages can appear on all conductors. When a vehicle is connected to the charger, the dangerous voltages will also appear on the chassis of the vehicle. When touched, it could complete the path to ground possibly causing a fatal electric shock.
By isolating the output of the supply, VEVA ensures that there is no risk of electric shock from the vehicle in the event of a broken PEN conductor.
The alternatives to built-in PEN protection (earth rod) and the differences.
1. Provide TT earthing for the charger circuit by installing an earth rod
Instead of earthing the charger to the TN-C-S sourced earth, the charger will instead be earthed using a TT earth electrode. This option will add additional time and cost to the installation and pose the risk of damaging underground cables / pipes when installed.
2. Supply EV charger from an isolating transformer
Additional cost and design considerations would be required.
VEVA’s inbuilt PEN protection provides an easy, low cost and low labour installation which is compliant with regulations.
What built-in protection does VEVA have?
VEVA continuously monitors the incoming supply and isolates Live, Neutral and Earth connections to the connected vehicle if the voltage exceeds 253V or drops below 207V. High voltage can signify an open circuit PEN conductor.
When in a fault condition VEVA will automatically recover from the condition when the supply voltage measured returns to a permissible range.
Inbuilt 6mA DC fault protection and 30mA Type-A RCD provide additional protection against risk of electric shock.
An additional safety feature detects if the output relay contacts were become welded (in a closed position). VEVA provides additional isolation to ensure Live and Neutral are isolated at the output when required.
Continuous monitoring of the supply load ensures that the charger does not contribute to the overall house load exceeding the supply fuse rating of the property.