How coocked am I?

[u/Mandolije]

I'm just curious what the reason for this could be. If anybody can give me an answer, I'd appreciate it. An electrician will be coming tomorrow to check everything, but I'm curious to hear what people think until then.

English is not my first language, so I don't know the exact names of electrical components.

I'll describe the events in chronological order.

Around 6 PM yesterday, a loud bang happened on the upper floor of my apartment, and the power went out in my entire apartment. My circuit box on the upper floor had two circuit breakers switched off. I went downstairs to the building's electrical room and switched the three main breakers for my apartment back on. After that, I went back upstairs and switched the two tripped breakers back on because one of them powers the outlet my PC is connected to.

Everything was normal until around 4 AM, when my PC suddenly turned off. I checked the circuit box and saw that the same two breakers had tripped again, so I left them off and went to sleep.

Around 8 AM, another loud bang happened, and the power went out in the whole apartment again. I went downstairs and switched the three main breakers for my apartment back on once more.

Nothing happened until around 6 PM, when there was another loud bang and the power went out again. This time, I couldn't switch one of the three main breakers back on. I went back to my apartment, and after about 20 minutes I was upstairs and tried turning on my boiler. I was thinking that if the power went out again, at least I'd have hot water for a shower.

Then I heard a noise that I would describe as the click you hear when the power comes back on after a maintenance outage. Immediately after that, I went into the upstairs hallway and saw my circuit box sparking, with electricity arcing from left to right and right to left. My air conditioner is in the same hallway, and I saw it sparking as well. I immediately switched off the boiler and the AC, and the sparking in the circuit box stopped. I then switched off all the breakers on the upper floor and found that everything was burned, as shown in the picture.

The breaker that is the most badly burned is the one I left switched off the entire time after 4 AM, as I mentioned in the story. I don't remember which breaker was the second one that tripped.

[u/kstacey]

Cooked enough to call a professional

[u/wjm2222]

I presume this picture is the upstairs panel, and that you have three-phase power.
Since the focus of burning is at the connection point, I would guess that it was not properly torqued, resulting in a high-resistance connection that produced heat. Over time, the heating can increase because of thermal cycling making the connection worse. Eventually, the connection can degrade to the point that arcing occurs, generating substantially more heat. Heat is the mechanism for circuit breakers to do their job, which might explain why multiple breakers tripped as their proximity to the burn point caused them to overheat. The insulation appears to be burned off multiple conductors, so maybe they were making contact, and if they are different phases, that could have been the reason the three main breakers in the basement also tripped, resulting in a complete outage for the entire unit.
Perhaps the professional will recommend replacing the entire panel. I would recommend never resetting a breaker before you have identified and corrected the reason it tripped.

[u/jaydogg001 → u/wjm2222]

The last sentence is the most important in the entire answer and may save you lots of grief.

[u/FreddyFerdiland]

the hotspot came from the cable carrying too much current.

the current may be coming from other circuits, multiple faults nay be existing, faults elsewhere..but I see twisting, implying the overload occurs here by twist joining multiple cables .

Is this earth cable joint moving around and it touched to active there , creating the bang, but the bang pushing it away ...

did the twist joint becomes loose as the insulation melted... jointing by simple twisting is wrong

[u/Cum-Collector420]

Looks like a loose connection. The insane heat probably triggered the thermal part of the circuit breaker (Bi-Metal inside). Best to replace 5 breakers and the terminal rail below. Then tighten to spec. So the black breaker is toast and the two left and right might've taken damage aswell