What Is a PEN Conductor? PEN Meaning, PME & Open PEN Faults
A PEN conductor is a conductor that combines the functions of protective earth (PE) and neutral (N). The term PEN comes from those two functions: PE + N.
PEN conductors are commonly associated with TN-C-S supplies using Protective Multiple Earthing (PME). The supply network uses a combined PEN conductor for part of the system before the protective earth and neutral functions are separated at the installation intake.
Quick answer: A PEN conductor combines protective earth and neutral functions in a single conductor. On a typical TN-C-S / PME supply, the PEN forms part of the supply network before being separated into PE (earth) and N (neutral) at the installation.
If that conductor becomes disconnected or develops a high resistance — commonly referred to as an open PEN or broken PEN fault — the potential of connected protective conductors and exposed metalwork can rise relative to true earth.
For installations where open-PEN protection is required, browse our PME Fault Detection Units.
| Term | Meaning | Function |
|---|---|---|
| PE | Protective conductor / protective earth | Protective earthing function |
| N | Neutral conductor | Carries normal return current |
| PEN | Combined protective earth and neutral conductor | Performs both protective and neutral functions |
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What Does PEN Mean in Electrical Terms?
PEN describes a conductor that performs both the protective earthing and neutral functions.
Rather than having separate protective and neutral conductors throughout the entire supply arrangement, the two functions are combined for part of the system.
That is different from:
- PE conductor: performs the protective earthing function only
- Neutral conductor: performs the neutral function only
- PEN conductor: combines both functions
The PEN conductor normally sits on the supply side of a TN-C-S installation rather than forming part of the customer's normal final-circuit wiring.
Simple definition: PEN = the combined protective earth and neutral conductor before those functions are separated into PE and N.
How Does a PEN Conductor Work on a PME Supply?
PEN conductors are commonly encountered in TN-C-S supply arrangements using PME.
In simplified terms, the arrangement works like this:
- The distribution network carries a combined PEN conductor.
- The PEN provides both neutral and protective earthing functions for that part of the network.
- The network PEN is earthed at multiple points as part of the PME arrangement.
- At the installation intake, the supply arrangement provides separate neutral and protective earth connections for the customer's installation.
- Inside the installation, neutral and protective conductors then perform separate functions.
This is why electricians will often hear PEN, TN-C-S and PME discussed together.
What Does PME Mean in Electrical Terms?
PME stands for Protective Multiple Earthing.
It describes the multiple earthing of the supply PEN conductor within the distribution network.
PME is therefore not another name for the PEN conductor itself:
- PEN = the conductor
- PME = the multiple-earthing arrangement associated with the supply
- TN-C-S = the earthing-system designation commonly associated with this arrangement
PE vs PEN Conductor: What’s the Difference?
A PE conductor and a PEN conductor are not interchangeable terms.
| Feature | PE Conductor | PEN Conductor |
|---|---|---|
| Protective function | Yes | Yes |
| Neutral function | No | Yes |
| Carries normal load current | Normally no | Yes, as part of its neutral function |
| Common location | Protective conductors within installations | Combined section of the supply network |
The fact that the PEN performs both functions is exactly why losing it can create a particularly serious condition.
What Is an Open PEN Conductor?
An open PEN occurs when the combined protective earth and neutral conductor becomes disconnected, broken or sufficiently high resistance that it can no longer perform its intended function correctly.
You may also hear this described as:
- Broken PEN conductor
- PEN conductor failure
- Lost PEN
- Open-PEN fault
- Open neutral on a PME supply
The fault can occur upstream of the installation, for example within the distribution network or supply connection.
The important point is that a PEN failure affects both the neutral reference and protective earthing arrangement because both functions were being carried by the same conductor.
Why Is a Broken PEN Conductor Dangerous?
An open PEN can create dangerous voltages between the installation's connected protective conductors and true earth.
Under normal conditions, accessible conductive parts connected to the protective earthing system should not present a dangerous touch voltage.
During certain PEN-failure conditions, however, the potential of the installation's protective conductors can rise relative to true earth.
That means accessible conductive parts connected to the installation earthing system can also rise in potential.
This becomes particularly important where somebody can simultaneously contact:
- Equipment connected to the installation protective conductor
- And true earth or conductive material at true-earth potential
Examples can include equipment installed outside a building or a vehicle being charged while the user is standing on the ground.
Key point: A PEN failure is not simply another overload or short circuit. Conventional overcurrent protection such as an MCB or fuse is not specifically designed to identify an open-PEN condition.
What Happens When a PEN Conductor Fails?
The precise electrical conditions depend on the network and connected loads, but a simplified sequence can look like this:
- The PEN conductor becomes open or high resistance.
- The normal neutral reference is disrupted.
- Load current can affect the potential of the remaining supply reference.
- The installation protective conductor system can rise above true-earth potential.
- Connected exposed-conductive-parts can rise to the same potential.
- A dangerous touch voltage can exist between that equipment and true earth.
This is the problem that open-PEN protective arrangements are designed to address.
Why Are PEN Conductors Important for EV Charger Installations?
EV charging receives particular attention because charging equipment is commonly installed outdoors and the vehicle itself is accessible while somebody may be standing in contact with true earth.
On an installation using a PME earthing facility, an open-PEN condition therefore needs to be considered as part of the EV charging design.
BS 7671 provides specific requirements for the use of PME earthing facilities for EV charging outdoors and allows several methods of addressing the open-PEN risk.
Depending on the EVSE and installation design, protection may be:
- Integrated into the charging equipment
- Provided by a separate open-PEN / PME protection device
- Provided through another permitted protective arrangement
So an EV charger on PME does not automatically mean adding a standalone PEN fault device. What matters is that the overall installation uses a compliant protective method.
What Is an Open-PEN Protection Device?
An open-PEN protection device is designed to identify supply conditions associated with a potentially dangerous PEN fault and disconnect the relevant conductors when its operating criteria are met.
You may see products described using terms such as:
- Open-PEN device
- O-PEN device
- PEN fault detection device
- PME fault detection device
- PEN protection unit
- PME protection unit
Different products can use different operating principles and voltage thresholds, so the correct device should be selected and installed in accordance with its manufacturer instructions and the installation design.
👉 Compare PME Fault Detection Units.
Is PEN Fault Protection the Same as RCD Protection?
No.
An RCD or RCBO and an open-PEN device are intended to deal with different fault conditions.
| Protection | Primary Function |
|---|---|
| RCD / RCBO | Residual-current / earth-fault protection |
| Open-PEN protection | Protection against dangerous conditions associated with failure of the supply PEN conductor |
| SPD | Protection against transient overvoltage |
One device therefore does not automatically replace the others where those separate forms of protection are required.
PME Fault Detection Units
Where the installation design requires a separate open-PEN protection unit, Power & Data UK supplies configurations for both single-phase and three-phase applications.
The range includes options incorporating combinations of:
- PME / PEN fault detection
- Type A RCBO protection
- Surge protection
- Outdoor IP-rated enclosures
- Single-phase configurations
- Three-phase configurations
- Load-management equipment
👉 Browse the complete PME Fault Detection range.
PEN Conductor FAQs
What is a PEN conductor?
A PEN conductor combines protective earthing and neutral functions within one conductor. It is commonly encountered on the supply network of TN-C-S / PME systems before the PE and neutral functions are separated for the installation.
What does PEN stand for in electrical terms?
PEN refers to the combined protective earth (PE) and neutral (N) functions of the conductor.
Is PEN the same as neutral?
No. A PEN conductor performs both a neutral function and a protective function. A normal neutral conductor performs the neutral function only.
Is PEN the same as PE?
No. PE is a protective conductor. PEN combines that protective function with the neutral function.
What is a PEN earthing system?
The phrase is commonly used when referring to TN-C-S / PME supplies where a PEN conductor performs combined protective and neutral functions on the supply network before those functions are separated at the installation.
What is PME in electrical terms?
PME means Protective Multiple Earthing. It refers to the multiple earthing of the supply PEN arrangement and is commonly associated with TN-C-S supplies.
Is PME the same as PEN?
No. PEN refers to the combined conductor. PME refers to the multiple-earthing arrangement associated with the supply system.
What is an open PEN?
An open PEN is a condition where the PEN conductor becomes disconnected, broken or sufficiently high resistance that it can no longer perform its intended protective and neutral functions correctly.
What is a broken PEN conductor?
It is another way of describing an open-PEN fault. Because the conductor performs both neutral and protective functions, its failure can create dangerous voltages between the installation earthing system and true earth.
Can an MCB detect a broken PEN conductor?
An MCB is designed primarily for overcurrent protection and is not an open-PEN detection device. Dedicated open-PEN protective arrangements are used where that particular risk needs to be addressed.
What is an open-PEN detection device?
It is a protective device designed to detect specified supply conditions associated with an open-PEN fault and disconnect the circuit or equipment according to its operating design.
Do EV chargers need open-PEN protection?
Where PME earthing is used for outdoor EV charging, the installation must use an appropriate protective method for the open-PEN risk. This may be incorporated within the charger, provided externally or achieved using another permitted arrangement.
Is an open-PEN device the same as a PME fault detection device?
The terms are often used for products intended to address the same underlying open-PEN risk, although individual devices can use different operating methods. Always check the manufacturer's specification.
Do I need an earth rod with PEN fault protection?
Not necessarily. One of the main reasons compliant open-PEN protective arrangements are used for EV charging is that they can provide an alternative to creating a separate TT arrangement. The correct solution depends on the complete installation design.
What Installers Need to Remember About PEN Conductors
A PEN conductor is simply a conductor performing both protective earth and neutral functions.
Three distinctions make the whole subject much easier to understand:
- PE = protective function
- N = neutral function
- PEN = both functions combined
On TN-C-S / PME supplies, those combined functions form part of the supply arrangement before being separated for the customer's installation.
The problem comes when that combined conductor fails. Because the neutral and protective functions are tied together upstream, an open PEN can cause the installation's protective conductors and connected metalwork to rise in potential relative to true earth.
That is why open-PEN protection receives particular attention on applications such as outdoor EV charging.
👉 Specifying an EV or outdoor installation requiring separate PEN protection? Compare single-phase and three-phase PME Fault Detection Units.