Rewiring older buildings: warning signs, process and what matters

Whether it is a Gründerzeit period building in Cologne's Südstadt, a post-war house in Hürth or a 1970s terraced house in the Rhein-Erft district: many buildings have an electrical installation that was never designed for today's demands. Back then there were few sockets, hardly any large appliances and no residual current devices (RCD, FI-Schutzschalter). Today, the induction hob, tumble dryer and home office all run at the same time – and soon perhaps a wallbox and heat pump as well.

Existing-installation protection – and its limits

An electrical installation that complied with the rules in force at the time it was installed may, in principle, continue to be operated. However, this existing-installation protection (Bestandsschutz) ends if

• the installation poses a hazard, for example due to damaged insulation, or
• the installation is substantially modified or extended – in which case at least the modified part must comply with today's standards.

In addition, anyone who lets property has a duty to maintain safety (Verkehrssicherungspflicht). Regular inspection of the electrical installation is therefore strongly recommended, even without an explicit legal obligation.

Warning signs of an outdated electrical installation

• Two-core cables without a protective conductor: Older buildings often lack the green-and-yellow protective conductor (Schutzleiter); sockets then have no effective earth contact.
• Fabric-covered or brittle cables whose insulation breaks when touched.
• Screw-in fuses without RCDs in the distribution board.
• Too few circuits: kitchen, bathroom and living areas are all on a single fuse that trips frequently.
• Warm sockets, switches or plugs, flickering lights or a smell of burning.
• Lots of multi-socket adaptors as a permanent solution because there are not enough sockets.

If several of these points apply, a qualified electrician (Elektrofachkraft) should inspect the installation. Measurements of insulation resistance and loop impedance quickly show what condition the installation is in.

Partial or complete refurbishment?

Not everything always has to be replaced. In practice, three levels have proven effective:

How a refurbishment works

1. Survey and measurement: condition of the cables, distribution board and meter cabinet (Zählerschrank).
2. Planning: number and position of sockets, lighting points and circuits – based on DIN 18015 and on your wishes, for example for a home office, smart home or network.
3. Meter cabinet and distribution: if necessary, a new meter cabinet and a new sub-distribution board with RCDs.
4. Cable installation: in chases, empty conduits or trunking – depending on the building fabric.
5. Testing: initial verification in accordance with DIN VDE 0100-600 with a test report (Prüfprotokoll).

Occupied buildings can often be refurbished in sections, so that part of the home always remains usable.

Planning for the future

If you are refurbishing anyway, you should think ahead to the coming years:

• empty conduits to the parking space for a future wallbox,
• space in the distribution board for photovoltaics, storage and a heat pump,
• network cables to studies and living spaces,
• surge protection and RCDs to the current standard.

We refurbish electrical installations in Cologne, Hürth and the Rhein-Erft district – find out more under Electrical installation and Testing & maintenance.