Power everywhere after turning off the main circuit breaker

Question

something weird happens in my house. I switched off the main circuit breaker for the house in order to change some light sockets and surprise - when i double checked with AC voltage tester I got positive on the light bulb socket. Not only that, I tried few more places - the tester detects power everywhere, but not only on the hot wires - the neutral ones started to trigger my tester too (before switching the breaker off, and after switching it on again i got power only from the hot wires only). I know the tester is good, as i have small diode indicator on the light switches and they are still working after turning off the main breaker. No lights or electric appliance worked tho, so i think it's some low voltage current flowing. So it seems when my main breaker is off - not only the power is still on, but it's flowing in the neutral wires too. What could be the problem?

Update: Every reading was measured also with phase meter and multi-meter with the same results.

Thanks!

Update 2: Photo of the circuit board with the breakers (old school):

Answer 1

It's possible the panel you have illustrated is one of several such panels serving power into the unit, so you may need to do an exhaustive search for any others.

It complicates things if this building has more than one unit. Wiring to the other units could be still energized obviously... And this could create false readings on test equipment (capacitive coupling) -- or there could be actual cross-connection between the units, so your unit might not be fully de-energized unless others are too.

Cross-connection could be a load in your unit served out of their circuit... Or even a neutral cross, where their load is served from their panel, but it uses the neutral on your panel, and if you sever that neutral wire which has current flowing through it, the upstream side will be energized to 230V.

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A lot of testers are complete junk, or are not made for house wiring and need some skill to successfully apply.

A common night light is surprisingly useful. It is simple, honest and not particularly reliable, which means you must check and double-check it. I honestly find them more useful than 3-lamp testers, though those are OK for a final check for new outlets.

Plain old analog voltmeters with the moving needle are useful.

Digital voltmeters (DVM) are useful but a little tricky. They are so sensitive they can pick up micro-currents from capacitive coupling, which happens when a dead wire runs physically parallel to a still-energized wire. So you have a DVM a reading of 109 volts on a 120V circuit that you thought was turned off - plug a night-light in, and the voltage mysteriously disappears.

If the electricity is powerful enough to illuminate any light, even an indicator light -- that's not capacitive coupling, that's genuine power.

Answer 2

If the Neutral is disconnected, but the live wire is not, and any appliances are connected then the Neutral will become live.

I guess your indicators are connected between Live and Earth and that is why they continue to operate, I have no idea if that is/was considered acceptable practice where you live.

There are several possibilities, one is that your "Main breaker" is faulty, another is that someone has wired up a device that takes its Live from somewhere other than your "main breaker" but its Neutral from your main breaker.

Either way extreme caution is needed when working on this installation.

You really need to get this looked at by someone who is familiar with local wiring practices where you live. I guess from the writing in your picture you live somewhere in the former Soviet Union and I doubt many people here are familiar with Soviet wiring practices.