What a main supply line is — in plain language
The main supply line (WLZ) is the section of the installation from the building's connection point to the distribution boards in the flats — a riser running through the stairwell, from which individual premises branch off. No one thinks about it because it 'always worked'. The problem is that buildings from the 1960s-80s (and older tenements) were designed assuming a consumption of 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 premises at similar times.
Symptoms that the main supply line is failing
- Dimming lights during peak hours (6-9 PM), 'soft' voltage;
- Overheating floor distribution boards and connection points — noticeable warmth, discolouration, smell;
- Frequent blowing of the building's main fuses;
- Refusals for residents' applications: for increased power, for an EV charging point, for a third phase to the kitchen;
- Aluminium in risers and pre-war cross-sections — visible whenever a niche on the stairwell is opened.
What modernisation looks like
- Inventory and measurements — actual condition of risers, connection point and distribution boards, peak loads; based on this, a design with future capacity (including for EV charging);
- Work floor by floor — power outages short and announced in advance, notices on stairwells, tenants know when and for how long;
- Switching over premises — each flat gets a new branch; this is also a natural moment to tidy up floor distribution boards and pre-meters;
- Common parts — stairwell and basement lighting, often together with the main supply line, because the walls are open anyway;
- Acceptance measurements and as-built documentation — a complete set for the administrator, with protocols for the building's logbook.
That this is not an exotic issue is evident in the municipal resources of the region: Świdnica's MZN in 2025 replaced common parts installations and main supply lines, among others, in buildings at Kraszowicka and Garbarska streets, and provided new power supply from the connection point to premises at Chopina street (according to MZN information on completed works). Where a building undergoes thermal modernisation, it is worth adding the main supply line to the scope — scaffolding and permits are already paid for.
For the administrator: where to start
Based on knowledge, not tenders. An inspection with measurements and thermal imaging of distribution boards shows which buildings in the portfolio require immediate action and which can wait — and provides solid arguments for community meetings. We manage this as part of property manager services, and to see what a full modernisation from design to protocols looks like, check out the case study of a 1920s tenement house.
Resident: if the administration refuses consent for higher power "because the building doesn't allow it" — this is exactly that issue. It's worth the community knowing the real condition of the main supply line (WLZ) instead of blindly rejecting further applications.
