PSU fails dramatically

[u/Front_Cookie_1198]

[u/DevLF]

Was my first thought too, but it appears the cables goes off somewhere behind and under the desk. Other end might not be easily accessible, definitely could use some safety improvements lol. Lucky it didn’t ground to the casing and electrocute him.

[u/Front_Cookie_1198 → u/DevLF]

I don't know why it didn't trip the circuit breaker.

[u/nxeyvzs → u/Front_Cookie_1198]

Circuit breaker only breaks if the breakers amperage limit ist hit. All cables and electronics should be able to survive until that limit ist broken. But sometimes you need a lot of power but divided into different components, like in a PC. The PSU is responsible for managing that. But If the PSU is fucked/badly designed then even If the amperage drawn from the Socket ist below the breakers limit, then something inside/behind the PSU might get more amperage than it can handle and burn. An RCD Breaker could prevent that but they are a bit more expensive and not mandatory in most places

[u/Antique_Paramedic682 → u/nxeyvzs]

You're not wrong, but also:

• Low draw, high heat: Panel breakers only care about current magnitude, not heat. A bad component can melt or burn at just 200–400W—way under a standard 15A/1,800W breaker limit.
• DC-side failure: If the short happens on the PSU’s internal DC output rails (like 12V), the AC side keeps pulling normal wall power while the inside melts.
• Failed internal protections: The PSU's built-in safeties (OCP/OTP/SCP) failed to shut it down, leaving the main panel completely unaware anything was wrong.
• Arcing heat: Loose connections or failing solder joints create intense sparking and fire without pulling enough continuous amperage to trigger a standard breaker.

[u/JaysFromMidToMenace → u/nxeyvzs]

The transformer will only pull whatever current it's rated for on the 115V side. In this case, 750W, which would be 6.5A.

After the transformer on the 12V/5V/3.3V side, if something happens like this, then the 115V side just keeps happily sending that 6.5A while the world burns :)

[u/Toraadoraa → u/Front_Cookie_1198]

Let's say the mofset popped, the customer unplugged his pc and took out the PSU. Did the rma process it shipped and arrived. The dead component had time to cool down and become more shorted. There's going to be a dozen or so components between the input and the blown shorted one, each basically is getting killed the entire path there. Those components don't take much power to blow up, especially when shorted. So the circuit breaker never gets a 15 to 20a load.

I the past you could do this in Germany if you had a pc from the usa a 115/240v switch. If you set it to 115 in Germany it blows up just like this.

[u/Soft_Lunch_183 → u/Toraadoraa]

I did this when i was younger with a japanese gamecube power supply + adapter, I had a PSP one that worked fine so I assumed it would be the same.

I plugged it in to 240v and it went up in smoke, luckily our sockets have switches on so i quickly flipped it off. Opened the window and my parents never found out

[u/JaysFromMidToMenace → u/Front_Cookie_1198]

Assuming the short circuit happened after the transformer, on the 12V/5V/3.3V rail side, then the circuit breaker would not break.

It says it's a 750W power supply. The transformer can therefore pull enough amps @ 115V to feed that 750W transformer, which is 6.5A. Assuming this was in a facility that was up to proper electrical code in the USA/Canada, then the breaker should be a 15A breaker for the 115V feed. 6.5A isn't enough to break the 15A breaker.

However, the 12V side was able to supply a lot of power past the transformer :) It only takes 1W to start a fire. This power supply could supply 750W :)

This is why you should never purchase budget PC components. I've had PC PSs go before from cheap parts. It's always dramatic and will start a fire.

[u/SickBurnerBroski → u/DevLF]

why in god's name would a repair place not have desk access for their power strip. some clownshoes here

[u/Annual-Advisor-7916 → u/DevLF]

Lucky it didn’t ground to the casing and electrocute him.

If you are trying to say that he's lucky that a condcutor carrying phase didn't somehow come loose and touched the case: That's one of the reasons why metal cases are always grounded - would trip the RCD.

But the ground seems to have a plastic surface, so even touching phase alone probably wouln't do anything - I've done it at least a couple times on plastic flooring as a kid.