If you’ve been researching EV charger protection, you’ve probably seen both terms:
PEN fault detection device and O-PEN device.
They’re often used interchangeably - but are they actually different?
This guide explains what each term means, whether there’s a technical difference, and how to choose the right solution for PME (TN-C-S) installs in 2026.
Quick Answer: An O-PEN device (Open PEN device) is a type of PEN fault detection device. Both are designed to detect dangerous conditions caused by a failed PEN conductor on PME supplies and disconnect the load. In practice, the terms describe the same protection function - but product designs and integration can differ.
🧭 Jump to:
What Is an O-PEN Device?
O-PEN stands for Open PEN.
An O-PEN device is designed specifically to detect when the PEN conductor on a PME (TN-C-S) supply becomes open circuit or unstable. When detected, the device disconnects the load to prevent dangerous touch voltages.
The term “O-PEN” simply emphasises the open-circuit condition being monitored.
What Is a PEN Fault Detection Device?
A PEN fault device describes the same core function - detecting unsafe supply conditions caused by a compromised PEN conductor and isolating the installation.
Rather than focusing only on the “open” condition, some manufacturers use the broader term “PEN fault detection” to describe monitoring of:
- Open circuit PEN
- High resistance PEN
- Voltage imbalance scenarios
- Supply reference instability
In practice, both terms refer to protection against the same risk.
Is There Any Real Difference?
Functionally, no.
Both O-PEN devices and PEN fault detection devices are designed to prevent dangerous touch voltages in the event of supply-side PEN failure.
| Term | What It Means | Practical Difference |
|---|---|---|
| O-PEN | Open PEN detection | Same core function |
| PEN Fault Device | Detection of unsafe PEN conditions | Same core function |
The difference usually comes down to branding and marketing language, not technical capability.
Integrated vs Standalone Devices
The real distinction installers should care about is not the name - it’s how the protection is implemented.
- Integrated Detection: Built into the EV charger.
- Standalone Device: Separate enclosure providing PEN/PME detection and isolation.
- Pre-built PME Board: Combined detection, isolation, overcurrent protection, and often SPD.
Many installers prefer standalone or pre-built PME boards for clarity during inspection and easier fault finding.
Installer Shortcut: A dedicated PME fault detection board keeps the protection layer separate from the charger and simplifies compliance verification.
Choosing the Right Device in 2026
Instead of focusing on the name, check:
- Is the supply PME (TN-C-S)?
- Is the EV charger external?
- Does the EVSE include certified open PEN detection?
- Does the device match single or three-phase supply?
If the charger does not provide compliant detection, a standalone PEN/PME detection unit is typically required.
FAQs
Quick answers to common terminology confusion.
Is O-PEN better than a PEN fault device?
No. They describe the same type of protection function.
Are O-PEN devices mandatory for EV installs?
Protection against open PEN conditions is mandatory where required under BS 7671. Whether built-in or standalone, a compliant method must be used.
Why do suppliers use different terms?
Mostly branding. Some prefer “O-PEN” to emphasise open-circuit detection, others use “PEN fault protection” as a broader term.
O-PEN / PEN Fault Detection Units for 2026 EV Installs
Whether you call it O-PEN or PEN fault protection, the hardware must match the supply configuration:
Single-Phase Domestic EV Installations:
👉 IP65 PME Consumer Unit – 40A Type A RCBO + SPD
👉 IP65 PME Consumer Unit – 40A Type A RCBO
Three-Phase & Commercial EV Installations:
👉 3-Phase PME Fault Detection Unit – 40RSP
👉 3-Phase PME Fault Detection Unit – 63A with SPD
All units provide monitored disconnection in the event of supply PEN failure on TN-C-S (PME) systems and are suitable for 2026-compliant EV installations.
Final Word
O-PEN device. PEN fault device. Open PEN detection.
The name matters less than the function.
- Match protection to the supply.
- Ensure compliance with BS 7671.
- Use a clear, inspection-friendly solution.
👉 Compare compliant PME / O-PEN detection units here: View PME Fault Detection Range.