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PEN Fault Detection

PlugStream includes built-in PEN Fault protection, designed to detect faults in the electricity distribution network that supplies the property. These faults only occur on TN earthing systems, where the Protective Earth (PE) and Neutral (N) conductors are combined in the supply cable.

UK Requirements

In the UK, the Wiring Regulations require EV chargers to isolate the Protective Earth conductor if a PEN Fault is detected. PlugStream provides this protection as standard.

It’s important to note that the international EV charging standard IEC 61851-1 does not permit interrupting the Protective Earth conductor. The UK has a specific derogation that allows this requirement to be implemented locally.

Worldwide (outside the UK)

In many countries, EV chargers must fully comply with IEC 61851-1, which prohibits interruption of the earth conductor. For these markets, we offer the “-E” version of PlugStream (“E” for Earth).

In this version, the Protective Earth conductor is never interrupted. If a PEN Fault is detected, PlugStream still reports the fault and disconnects Line and Neutral, but the Earth conductor remains connected — meaning there is still a potential risk of electric shock.

Operation

PlugStream’s integrated PEN Fault protection complies with BS 7671:2018 Amendment 1:2020 clause 722.411.4.1 (iv).
The system triggers if the charger detects:

  • More than 253 V rms, or
  • Less than 207 V rms
  • …between Line and Neutral, for longer than 5 seconds.

When triggered:

  • Line, Neutral, and Earth connections to the vehicle are disconnected.
  • The charger displays a red light, and charging is stopped if in progress.
  • After the supply voltage returns to normal for 30 seconds, the charger resets automatically.

Behaviour after reset:

  • If idle: returns to ready mode (green light).
  • If charging: resumes charging (green pulsing light), up to 10 times.
  • After 10 retries, the charger locks out permanently (red light). To reset, disconnect and reconnect the charging cable.

What should I do if a PEN Fault is detected?

A PEN Fault indicates that the supply voltage has moved outside statutory limits. This is a serious safety issue and must be reported to the local Distribution Network Operator (DNO) by dialling 105 in the UK.

The DNO will investigate and make any necessary repairs.

Additional diagnostic information is stored by the charger and can be provided by contacting PlugStream Support.

Why is PEN Fault protection necessary?

In the UK, EV chargers used outdoors must be protected against neutral faults on PME networks (Protective Multiple Earth). This is a legal requirement under IET Wiring Regulation 722.411.4.1.

Here’s why:

  • In PME systems, Earth and Neutral are combined into a single PEN conductor.
  • If the PEN conductor becomes disconnected (“open PEN”), dangerous touch voltages can occur.
  • A person touching an EV connected to a charger and a true earth reference (e.g. a metal fence) could receive a fatal shock.
  • Standard RCD protection does not detect this condition.

To prevent this hazard, the charger must either be supplied by a dedicated earth or include PEN fault protection that disconnects Line, Neutral, and Earth to the vehicle if a fault is detected.