Protective earthing (PE)
§411 — Protective earthing (PE)
Protective earthing ensures that conductive enclosures of equipment are connected to earth so that an insulation fault cannot leave a dangerous voltage on touchable parts.
Color codes per NEN 1010
- Brown: line (L)
- Blue: neutral (N)
- Green/yellow: protective earth (PE)
For TN-C-S installations: PE and N are separated downstream of the split point.
The five earthing systems
NEN 1010 distinguishes five earthing systems, identifiable by a two- or three-letter code that describes how the supply and the enclosure (the exposed-conductive-part) are connected relative to earth:
| System | Supply relative to earth | PE/N arrangement | Typical use |
|---|---|---|---|
| TN-S | One point directly earthed | PE and N separated throughout the entire installation | New-build, industrial installations — preferred because no current flows over PE and RCDs operate correctly |
| TN-C | One point directly earthed | PE and N combined in a single PEN conductor | Only permitted upstream of the split point; not in final circuits |
| TN-C-S | One point directly earthed | PEN from the grid operator, split into PE and N at the meter cupboard | Most common in Dutch dwellings (often referred to as PME) |
| TT | One point directly earthed | Own earth electrode at the installation, independent of the network earth | Greenhouses, temporary installations, sites without a reliable PEN — always with an RCD |
| IT | No direct earthing, or via high impedance | Isolated from earth; a first fault does not immediately cause disconnection | Hospitals (operating theatres), industrial continuous processes where loss of supply on a first fault is undesirable |
Exam rule of thumb: "1010 builds, 3140 works" — the system is chosen at the design stage (NEN 1010); TN-S is preferred in practice setups and new-build because the separated PE carries no leakage current, so an RCD trips reliably.
Practical example — greenhouse installation
In horticulture, outdoor panels are often fed via PME (TN-C-S) or a TT system. For TT, an RCD (§531) is mandatory.
Common mistakes
- Connecting PE to water or gas pipes (prohibited since NEN 1010-2015).
- PE in the same busbar as N downstream of the split point.
- Forgetting the protective conductor on Class I luminaires.
Related
- §413 — Automatic disconnection of supply
- §531 — Residual current devices
- Conductor colors (NEN-EN 60446)