An open PEN event doesn’t always announce itself clearly.
In many cases, what installers see first are strange voltage readings, flickering lights, or unexplained instability - before the root cause is identified.
This guide explains the real-world symptoms of PEN loss, what tools installers use to detect unsafe conditions, and how modern PME fault detection devices respond in 2026.
Quick Answer: PEN loss (open PEN) can cause voltage imbalance, rising touch voltages, and unstable neutral reference. Installers may observe fluctuating voltage readings or equipment instability. Modern PEN detection devices continuously monitor supply conditions and disconnect automatically if unsafe thresholds are reached.
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Common Symptoms of PEN Loss
When a PEN conductor becomes open circuit or high resistance, symptoms may include:
- Flickering or unusually bright/dim lighting
- Voltage readings drifting above or below nominal 230V
- Unexpected tripping of equipment
- Metallic parts showing abnormal voltage to true earth
- Customer reports of “strange electrical behaviour”
On three-phase systems, imbalance between phases can become severe, particularly under uneven loading.
What Actually Happens to Voltage During PEN Loss?
On a PME supply, the PEN conductor provides the neutral-earth reference.
If it becomes compromised:
- The neutral reference shifts.
- Load imbalance affects voltage distribution.
- Line-to-neutral voltages can rise or fall unpredictably.
In extreme cases, one circuit may experience overvoltage while another drops significantly below nominal.
This instability is why PEN loss is considered hazardous in EV installations.
Tools Installers Use to Detect Issues
Installers may use:
- Multimeters for voltage measurement
- Clamp meters for load assessment
- Voltage recorders or power quality analysers
- Continuity testing for supply integrity
However, detecting intermittent or upstream PEN faults manually can be difficult. Many supply-side failures occur outside the property boundary.
Important: Test pens and basic plug-in testers are not suitable for assessing PEN integrity.
How Modern PEN Detection Devices React
Modern PME fault detection units continuously monitor:
- Line-to-neutral voltage
- Neutral-to-earth potential
- Voltage imbalance conditions
If unsafe thresholds are exceeded, the device:
- Detects abnormal supply reference behaviour.
- Triggers internal isolation.
- Disconnects all live conductors.
This automatic disconnection prevents dangerous touch voltages from persisting at the EV charger or connected equipment.
Why PEN Loss Detection Is Critical for EV Installations
EV chargers connect directly to vehicle chassis, which are large conductive structures.
In the event of an open PEN:
- The vehicle body could rise in potential relative to true earth.
- The user may be standing outdoors on ground potential.
- Touch voltage risk increases significantly.
This is why BS 7671 places specific emphasis on protection against supply PEN conductor failure in EV installations on PME systems.
Installer Reminder: Detection must match the supply configuration - single-phase or three-phase - and be correctly rated for the installation.
FAQs
Quick answers to common diagnostic questions.
Can a PEN fault trip a normal RCD?
Not necessarily. RCDs detect residual current imbalance, not supply reference instability.
Is PEN loss common?
It is not common, but the consequences can be severe enough that protective measures are required where risk exists.
Can I test for open PEN safely myself?
Testing supply-side integrity should be carried out with appropriate equipment and competence. Many faults occur upstream of the installation.
PME / PEN Fault Detection Units for 2026 Installations
If voltage instability or PEN risk is a concern on a PME supply, use a detection unit matched to the supply configuration:
Single-Phase Domestic EV Installations:
👉 IP65 PME Consumer Unit – 40A Type A RCBO + SPD
👉 IP65 PME Consumer Unit – 40A MCB + SPD
Three-Phase & Commercial Installations:
👉 3-Phase PME Fault Detection Unit – 40RSP
👉 3-Phase PME Fault Detection Unit – 63A with SPD
All units continuously monitor supply conditions and disconnect automatically if unsafe PEN conditions are detected on TN-C-S (PME) systems.
Final Word
PEN loss can present subtly - until it becomes dangerous.
- Understand the symptoms.
- Use appropriate diagnostic tools.
- Install compliant PEN detection where required.
👉 Stay protected and inspection-ready - compare PME fault detection units for 2026 installs.