⚠ Safety note: This guide involves working with electricity. If you're not completely sure about every step, stop and call a licensed professional. Before you start, always switch off the power at the breaker or close the main water/gas valve.
1 Prepare for safe work
Switch off the corresponding fuse or main switch, prevent accidental reactivation, and confirm the absence of voltage with a two-pole voltage tester. If you cannot reliably identify the electrical circuit, stop working.
⚠ Warning: A series switch is not the same as a two-way switch. If the terminal layout is not clearly marked, do not connect using trial and error.
2 Determine the problem pattern
Mark the common phase supply wire and two separate return wires to the two groups of lighting before turning off.
3 Check the most common cause
Connect the supply phase to the common L terminal, and each return wire to its output according to the diagram of the specific switch.
4 Apply the appropriate solution
Before replacing the cover, verify that each button controls only the intended group and that there is no exposed copper.
? Tip: Photograph the initial state and change only one thing at a time to know which check really affected the result.
5 Test the result and set the limit
Put the covers and safety guards back before switching on. Turn on the power from a safe distance and turn off immediately if a spark, odor, heat, humming, or a trip of the protection occurs.
When to call a professional: If the job involves changes to the electrical panel, the main gas line, or load-bearing walls/beams — or if you're not sure how it will turn out — this is not a DIY task. Hire a licensed professional.