Once you’ve established that PEN fault protection is required, the next question is simple:
Do I need a 1-phase or 3-phase PEN detection device?
The answer depends entirely on the supply type and the charger or equipment being installed. This guide breaks down the differences, where each is used, and how to choose correctly in 2026.
Quick Answer: Use a 1-phase PEN detection device for standard domestic EV chargers on single-phase PME supplies. Use a 3-phase PEN detection unit for commercial or high-load EV installs on three-phase PME systems. The device must match the supply configuration.
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1-Phase PEN Detection Devices (Domestic EV Installs)
Single-phase PME supplies are the norm in UK domestic properties. Most home EV chargers operate on 230V single-phase.
You’ll typically need a 1-phase PEN detection device when:
- The property is on a PME (TN-C-S) supply.
- The EV charger is installed externally.
- The charger does not include compliant built-in open PEN detection.
These units monitor voltage conditions between line, neutral and earth, and disconnect the circuit if an unsafe open PEN condition is detected.
Most domestic installs fall into this category.
3-Phase PEN Detection Devices (Commercial & High-Load)
Three-phase supplies are common in:
- Commercial premises
- Workshops
- Industrial units
- Multi-charger EV sites
On a three-phase PME system, an open PEN can cause significant voltage imbalance between phases. The resulting instability can be more severe than on single-phase systems.
A 3-phase PEN detection unit monitors all phases and isolates the load if unsafe conditions occur.
Installer Note: If you’re installing 22kW chargers or multiple EV points on a 3-phase PME supply, use a dedicated 3-phase PME detection unit rather than adapting a 1-phase solution.
What’s Technically Different Between 1-Phase and 3-Phase Units?
| Feature | 1-Phase Unit | 3-Phase Unit |
|---|---|---|
| Supply Type | 230V Single-Phase | 400V Three-Phase |
| Poles | 2-Pole Isolation | 4-Pole Isolation |
| Voltage Monitoring | L-N-E | L1-L2-L3-N-E |
| Typical Use | Domestic EV Chargers | Commercial / Multi-Charger Sites |
The key rule: match the detection device to the supply configuration.
How to Choose Correctly in 2026
Run through this quick checklist:
- Confirm supply type at intake (single or three-phase).
- Confirm earthing system (PME / TN-C-S).
- Check whether the EV charger includes compliant open PEN detection.
- Select a detection unit that matches the supply and load.
Where doubt exists, installers typically favour a dedicated PME detection board with integrated isolation and SPD.
FAQs
Quick clarifications for spec stage.
Can I use a 1-phase PEN device on a 3-phase supply?
No. The protection device must match the supply configuration.
Do 3-phase chargers always require 3-phase PEN protection?
Yes, if installed on a 3-phase PME supply where open PEN risk exists.
Is 3-phase PEN protection more important than single-phase?
Voltage imbalance during an open PEN event can be more severe on three-phase systems, making correct detection critical.
1-Phase vs 3-Phase PME Detection Units (2026 Spec Guide)
Single-Phase Domestic EV Installs (Most Common):
👉 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
Managed / Multi-Charger Installations:
👉 IP65 PME Unit with Load Balancing Relay + kWh Meter
All units are suitable for 2026-compliant EV installations on TN-C-S (PME) supplies and provide monitored disconnection in the event of supply PEN failure.
Final Word
The difference between 1-phase and 3-phase PEN detection isn’t about preference - it’s about matching the protection to the supply.
- Domestic single-phase EV install? → 1-Phase PME device.
- Commercial or 22kW EV on 3-phase PME? → 3-Phase PME device.
👉 Spec it correctly first time - browse the full PME Fault Detection range.