Electrical installation in old buildings – safe and standard-compliant renovation
Old buildings have their charm—but often also outdated electrical installations. Classic grounding, fabric wiring, and missing residual current circuit breakers are typical problems. This guide shows you what to look out for when renovating electrical systems and how to modernize them step by step.
Attention: Old building
- Traditional grounding (TN-C) is dangerous and must be changed
- Retrofitting RCD circuit breakers is the most important immediate measure
- In the event of substantial changes, current standards apply (DIN VDE 0100).
Typical conditions in older buildings
Buildings constructed before 1990 often have the following problems, which should be remedied during renovation:
Classic neutralization (TN-C)
The neutral conductor and protective conductor are combined. In the event of an interruption, the housing is live – danger to life! Recognizable by only 2-wire cables.
Fabric conduits & aluminum cables
Rubber-insulated fabric cables are brittle and pose a fire hazard. Aluminum cables break at the clamping points and have higher resistance.
No ground fault circuit interrupter
Before 1984, RCDs were not mandatory. Without an RCD, vital residual current protection is lacking for all sockets and bathrooms.
Conversion from TN-C to TN-S
What do TN-C and TN-S mean?
In the TN-C system, the neutral and protective conductors are a single conductor (PEN). In the modern TN-S system, they are separate (N and PE). An RCD circuit breaker only works correctly in the TN-S system.
Why is the change necessary?
No RCD can be used without separating N and PE. The RCD only detects fault currents if N and PE are separated. In addition, there is a risk of fatal injury if the PEN conductor is interrupted.
How will the change be implemented?
The separation takes place at the house connection box (HAK). From there, N and PE are routed separately. This usually requires a new supply line to the meter cabinet and a new meter cabinet.
Retrofitting obligations – When MUST renovation work be carried out?
Grandfathering does not mean that old installations can remain in place indefinitely. In the event of substantial changes (e.g., installation of a new kitchen, bathroom renovation, addition of a wall box), the affected electrical circuits must be brought up to current standards (DIN VDE 0100). Even in the event of a change of ownership or rental, the owner is responsible for ensuring that the electrical installation is in a safe condition.
Step-by-step modernization – setting priorities
Inventory and inspection
E-check by a qualified electrician: insulation measurement, loop impedance, testing of protective measures. Documentation of the current status.
Retrofitting residual current circuit breakers
Most important immediate measure! Install residual current devices (30 mA) for all socket circuits. In the TN-C system, switch to TN-S beforehand.
Renew critical electrical circuits
Bathroom, kitchen, and outdoor areas first. Replace fabric conduits and aluminum cables. Install new conduits with sufficient cross-sectional area.
Modernize meter cabinet
New meter cabinet with sufficient space units, modern circuit breakers, SPD, and reserve space for wall box, PV, and smart home.
Practical tips for renovating old buildings
1. Recognizing classic zeroing
Only 2-wire cables (phase + PEN) indicate classic neutralization. Even if yellow-green conductors are present: Check whether N and PE are really separated.
2. Retrofitting RCDs saves lives
A residual current device (30 mA) prevents fatal electric shocks. Retrofitting costs a few hundred euros and is the most effective safety measure.
3. Install empty conduits during every renovation
If walls are being opened up anyway, lay empty conduits at the same time! This will enable subsequent extensions (network, smart home, additional electrical circuits) to be carried out without the need for chiseling.
4. Inventory with test report
Before any renovation: Have an electrical inspection carried out. The inspection report documents the condition and indicates the most urgent measures. Important for insurance and liability.
Conclusion: Renovating electrical systems in older buildings is worthwhile—for safety and value.
A modernized electrical installation protects residents, reduces the risk of fire, and increases property value. A step-by-step approach makes costs predictable.
Important: Work on electrical installations may only be carried out by registered electrical contractors. DIY work is prohibited when dealing with high-voltage current.