EV Charging

Introducing TruePEN, safer by design

Sultana Rahman

13 October 2021, 08:30:04

A safer and compliant electric vehicle charging solution for the home.


Rolec’s TruePEN system provides customers with a safer and compliant electric vehicle charging solution, ensuring that current regulations are met. The built-in TruePEN PME fault detection allows for a cost-effective and quicker installation process, without the requirement for an earth electrode/rod.


What is PME Fault Detection?


A Protective Multiple Earth (PME) system is wired in many UK homes. In a PME system, the home’s earth wiring is connected to the neutral conductor at the mains supply connection point entering the home. The combined Protective Earth and Neutral (PEN) is then earthed multiple times on its route back to the sub-station. The low impedance path provided between neutral, and earth ensures RCDs fitted in the home consumer unit reliably detect earth faults.


A home EV charge point when installed is connected to the same point, allowing the PEN conductor to provide connection back to earth.


A possible fault condition in a PME system occurs when due to a break in the PEN conductor the home appliances appear dead. However, if a device is turned ON the neutral will rise to the live potential, and so too will earth as this is also connected to the house neutral. Under this fault condition RCDs no longer provide fault protection.


Inside the home the danger is low as no potential difference exists between the live, neutral and earth conductors to do any harm. However, if a vehicle is connected to the charge point and earthed inside the home this provides high risk of electric shock due to the potential difference between vehicle chassis and external ground. If a person stood on the ground touches the vehicle chassis, they could complete the earth’s path to ground and experience an electric shock.


The 18th Edition of the IET Wiring Regulations (BS7671:2018) addressed this problem under clause 722.411.4.1 on the installation of EV charge points for domestic installations.


Protecting a person in the event of this fault condition can be achieved by installation of an earth rod at the charge point, or through PEN fault detection and isolation of vehicle from home live, neutral and earth. The latter is often preferred due to low cost and easy fitment.


Why Rolec have developed TruePEN


The inclusion of PEN fault detection within the IET Wiring Regulations allowed for a lower cost alternative to the ground rod and following this many PEN solutions quickly appeared.

However not all conform to regulations with High and Low voltage detection thresholds out of tolerance and only live and neutral being isolated.


(Some non-UK markets support High and Low voltage detection but this can be miss interpreted as PEN fault detection/protection)


We started our internal research and development to precisely meet the regulations and therefore implement a true PEN solution. On our path we confirmed repeatability and tolerance over environmental operating range and tested electro-magnetic compliance to ensure safety is not compromised.

The TruePEN system


Following power on TruePEN monitors the supply voltage for 5 seconds and determines if the voltage is within normal operating limits. (No differentiation is necessary between 230Vac or 240Vac supply).


If out of limits a PEN fault condition is activated. To clear, the supply must return within normal operating limits, and may also require a power off/on cycle should the cause have been an over-voltage condition.


If within limits TruePEN allows connection of live, neutral and earth to the vehicle, and continues to monitor the supply. If the voltage drops below 207Vac and does not return for up to 5 seconds, a PEN fault condition is tripped and live, neutral and earth connections are removed from the vehicle.

However, a voltage dip could also cause the same fault condition. Therefore, TruePEN continuously monitors the supply health and if it returns to within normal operating range, automatically allows reconnection of live, neutral and earth to the vehicle.


The charge session can then resume without manual intervention and the EV driver is not inconvenienced.

If the voltage rises above 253Vac and does not return for up to 5 seconds, a PEN fault condition is tripped and live, neutral and earth connections are removed from the vehicle.

TruePEN continues to monitor the supply heath but if it returns to within normal operating limits the fault condition is not cleared without manual intervention to power cycle.

Under this condition the EV driver is made aware of the high-voltage applied to the vehicle and can then perform safety checks before driving the vehicle.


In summary TruePEN Functions


  • Automatically monitors the supply voltage on both 230V & 240V supplies without the need for any manual dipswitch settings.

  • Within 5 seconds in the event of an under-voltage of less than 207V or an over-voltage of more than 253V Live, Neutral & Earth will be isolated.

  • Following an under-voltage isolation, will automatically reset when normal operating range is restored.

  • Following an over-voltage isolation, on the grounds of safety, will require a manual reset.

  • TruePEN is the low cost, labour effective solution to meeting regulatory requirements when fitted to a charge point to a PME system.

TruePEN is the low cost, labour effective solution to meeting regulatory requirements when fitted to a charge point to a PME system.


Click here to pre-order now for mid-November delivery!

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