What a mains distribution line (WLZ) is - in plain English
The mains distribution line (WLZ) is the section of the installation from the building service connection to the distribution boards in the flats - a riser running through the staircase, from which individual units branch off. Nobody thinks about it because "it has always worked". The problem is that buildings from the 1960s-1980s (and older tenement houses) were designed assuming a consumption of around 1-2 kW per flat: lighting, radio, TV, washing machine. Today, a single flat can temporarily consume several times more - induction hob, dishwasher, air conditioner, kettle - and this happens in all units at similar times.
Symptoms that the mains distribution line (WLZ) cannot cope
- dimming lights during peak hours (18:00-21:00), "soft" voltage;
- heating floor distribution boards and connections - noticeable heat, discolouration, smell;
- frequent blowing of the building's main fuses;
- rejections of residents' applications: for capacity upgrades, for a car charging point, or for a three-phase supply to the kitchen;
- aluminium in the risers and pre-war cross-sections - visible every time a recess in the staircase is opened.
What modernisation looks like
- Inventory and measurements - the actual condition of risers, connections, and distribution boards, peak loads; based on this, a design with spare capacity for the future (including EV charging);
- Staircase-by-staircase work - power outages are short and announced in advance, notices on the staircases, tenants know when and for how long;
- Reconnecting units - each flat gets a new branch; this is also a natural moment to tidy up floor distribution boards and pre-meter devices;
- Common areas - lighting of staircases and basements, often done together with the mains distribution line (WLZ), as the walls are open anyway;
- Acceptance measurements and as-built documentation - a complete set for the property manager, with reports for the building log book.
That this is not exotic can be seen in the municipal resources of the region: Świdnica MZN in 2025 replaced installations of common areas and WLZ, among others, in buildings at Kraszowicka and Garbarska, and brought a new power supply from the connection to the premises at Chopina (according to MZN information on completed works). Where a building is undergoing thermal modernization, it is worth adding WLZ to the scope - scaffolding and permits are already paid for.
For the manager: where to start
From knowledge, not from a tender. An inspection with measurements and thermography of distribution boards shows which buildings in the portfolio require action now and which can wait - and gives hard arguments for a community meeting. We conduct this as part of our property managers service, and to see what a full modernization from design to reports looks like - see the case study of a tenement house from 1920.
Resident: if the administration refuses consent for higher power "because the building does not allow it" - this is exactly the topic. It is worth for the community to know the real state of the WLZ, instead of blindly refusing subsequent applications.
