Isolate, lock, prove dead
Switching off the main breaker of your own panel is not isolation. Isolation means opening the device upstream of the panel — the utility cut-out, meter breaker or the breaker in the building's distribution board that feeds your line.
- Switch off at that upstream device, then lock it off or remove its handle; if it cannot be locked, tag it and keep it in sight.
- Tell everyone in the home that you are working. A helpful neighbour restoring power is a classic accident.
- Verify absence of voltage with a two-pole tester, never with a non-contact pen alone.
- Prove the tester on a circuit you know is live, then test the panel, then prove the tester again. A tester with a flat battery says "dead" about everything.
In many apartments the isolating device is sealed and belongs to the network operator — in the EU the meter cut-out, in CIS countries the sealed incoming breaker. You may not break that seal yourself: call the operator and have them isolate.
What stays live with the main breaker off
The incoming cable and the top terminals of your main breaker remain at full mains voltage no matter what you switch inside the panel. Nothing you do at your own board changes that. Treat that part of the enclosure as live at all times, and if your work touches it, the supply must be isolated upstream — that is the operator's or an electrician's job.
The same applies to anything wired ahead of the main breaker, such as a meter connection or an unswitched feed to a sub-panel.
Rules for your hands
- Never work on a live panel. Working live is a defined professional competence with its own equipment and procedures, not a shortcut for a confident DIYer.
- Use insulated screwdrivers rated 1000 V, and eye protection when cutting or drilling.
- Dry hands, dry clothes, dry floor. No standing in a puddle, no working outdoors in rain, no damp cellar floor.
- Remove rings, watches and metal bracelets before you start.
- One hand in the panel, the other out of it. A hand-to-hand path runs current straight across your heart.
- Work in good light, with the panel cover off and the space in front of it clear.
- Never trust a circuit that "should" be off — test it.
Where DIY stops
Planning a panel, buying the parts, mounting the enclosure and preparing the wiring are things you can reasonably do yourself. The final connection to the supply, the energization and the verification are a licensed electrician's job — insulation resistance, earth loop impedance, earth electrode resistance and terminal torques all need instruments and professional responsibility, and in most jurisdictions the paperwork is legally required.
If the earthing system in your home is not clearly identified, stop before you connect anything to PE (earthing systems). And when your project drifts outside ordinary residential work, hand it over (when to call an electrician).