My problem
Occasionally, I lose power in all circuits of the home (at the same time), for about 1 second (sometimes more, sometimes a fraction of a second).
Power comes back automatically, and none of the switches in my circuit breaker flipped.

Triggers
Happens quite randomly, but only when using any 1 of these 3 devices. I've tested each individually, and any one by itself can cause the issue. I highly doubt all 3 have gone bad at the same time.
A) Yamaha Aventage A870 sound amplifier. Approx 200W continuous, ~600W peak. Double-isolated (doesn't have an earthing connector).
B) BK Elec XLS 200 subwoofer. 275W continuous declared on the back (in reality it's a bit more). Peak probably 900W. 3 prong plug.
C) Cambridge Audio Minx X301 subwoofer. 350W continuous. Peak probably 900W. 2 prong plug.
The issue doesn't always occur when there's sound playing. It has happened twice with no sound playing at all (movie being paused).
I don't listen anywhere near their max volume.

Other home appliances
Electric oven, electric cooker, dishwasher, desktop PC, hairdryer... basically anything else in the home, can be used without problems.

Testing on another circuit
These 3 devices are plugged into the 'flat' wall sockets.
I temporarily moved device A to a kitchen wall socket. Issue still happens.
I've also isolated the 'flat' ring by turning off every other switch in the breaker box. Issue also happens.

UK Power Networks
I contacted UK Power Networks about this, once right after an occurrence so they could check for issues in real time.
They don't see any fault on their side. If the whole phase is bad, 1/3 of my building would be having my issue.
Asking on my building's community forum, nobody has my issue.
I'm in a flat in a large building, so UK Power Networks doesn't handle the final distribution board.
I've notified building management asking to check the internal distribution board, but they haven't come back to me yet.

Electrician visit
I called in an electrician to check. He tested the breaker box, re-tightened everything, even replaced a wire that was suspiciously loose, checked the electric meter. Didn't find any issue.
Issue still persists after the visit. The electrician has no idea what else to do.

Any idea what the problem is? I have no idea what else to do to diagnose or fix this.
The problem is also quite random and hard to reproduce (obviously nothing goes wrong when the electrician's in the home).

 

You say that "Electric oven, electric cooker, dishwasher, desktop PC, hairdryer... basically anything else in the home, can be used without problems."
So it would seem you have problem with some of the audio visual units only?
Most of the above large appliances, you may not notice a momentary stoppage anyway.
Can you use any of the items in a different premises and find out if it is actually the service supply?
Max.

 

You are right at saying that oven and other things don't suffer from short interruptions.
I can very clearly notice when there is one of these interruptions because:
- all lights blink out, it's quite obvious
- even if I don't notice the lights blinking, short interruptions cause my AV receiver and desktop PC to reboot (longer than 1s interruptions cause them to stay off)

Unfortunately there is no easy way to test my equipment somewhere else, especially now during lockdown.

Yes, for now I think that only my audio equipment can cause the problem.
They don't much power, but don't use a constant amount of power, they do generate a very spiky electric load.
The Yamaha and BK use class AB amplifiers. I'm not an electric expert myself but maybe this info can be useful for someone.

What if this is somehow related to sound vibrations?
Although the problem doesn't always occur when there's sound playing...

 

If all lights are blinking out - my guess would be a bad connection at the meter.

Years ago I rented an apartment. Randomly I'd lose half the circuit. (U.S. power consists of two lines and a center tapped neutral - each line is 120VAC to neutral and from line to line is 240VAC) When I would turn the electric stove or oven on all lights would come back on and function properly for a period of time. But inevitably the same thing would occur again. I called the landlord time and again but every time he came the lights had come back on. We lived with that for a few months till finally, the lights went out and didn't come back on. He got his electrician out to investigate. The problem was a corroded connection at the power meter. When you turned the oven on there was enough current draw to partially weld the weak connection together. But it would eventually fail again. When the bad connection was fixed - that was the end of the problems.

It sounds like you're experiencing something similar. It could be a poor connection somewhere or it could be a bad main breaker. Even if it doesn't trip it could still be interrupting power. Best advice is to have someone qualified and licensed look at the problem and either recommend a fix or fix it outright. I'd opt for the outright fix. Especially if you're a renter. Me - as a home owner - I would tackle some jobs, but others I know better than to mess with at my skill level.

 

I did a test today.
Connected the Yamaha (device A) to a UPS. Then flipped off the wall switch of the UPS to make it run on battery.
Made sure UPS is on battery mode as its inverter makes a buzzing noise and also beeps periodically.
Played some music.
Power blinked out after just a few minutes.

??????????

What I'm thinking now:

• with this test, almost certainly issue not caused by power draw. The AVR wasn't drawing any power from the wall outlet in this case.
• could be sound vibrations making something loose? Seems strange but maybe possible.
• neighbours cutting off my power because they can hear music from my side? Maybe I'm becoming crazy...

 

Breakers do not trip when the mains power collapses. We commonly joke that we live in a "third world country" when the mains power goes out for both short and long intervals in bright sunshiny weather. Many devices, like my binary LED clock, display a distinctive pattern when the power goes out. The good news is that we can text or call Duke energy for an estimate of when the power will return. Their estimates are conservative and are usually met long before the claimed duration of the outage. They also aggressively cut tree branches anywhere near the power lines leading some amusing tree sculptures and landscapes.

 

With the tests you have done, my suspicion, like yours is something in the equipment itself, such as a thermal shutdown or overcurrent shutdown. Brownout (LV) shutdown is a possibility, but I suspect it is less likely than the former.

Do you have a typical digital clock without power backup? That is, one that resets or shows PF when power in interrupted for only a short time. I would borrow a clamp ammeter, put it on the supply line to one of the devices and plug the clock into the same outlet. Then look for a dip in the ammeter and no loss of clock power.

The clock is only functions as a control for the test. Once you isolate it to a device, then I would open it and start looking for some sort of resettable "fuse."

 

In addition to a possible equipment problem, it could be a line cord problem, possibly with the molded on plug. Over the years I have seen several such problems, To see if that is the cause you can flex the line cord and see if that causes the symptom.