Almost killed my Rig

OMG was just working on my main PC shifting some fans about trying to optimise Airflow / Noise. PC was running so I could listen to the fans, I had finished and was fan cable tidying and SPARK!!!! PC died. tried to re-start and nothing, tried again nothing... tried to stay calm, pulled out the HDD and connected it to my laptop to check it wasn't fried as all the other testing would have to wait till tomorrow... HDD okay data intact. So I thought I'd have one last power button try and Beep, post, yahay!

Fan was connected directly to PSU molex and it must have flipped an overload switch, maybe someone on the forum can elucidate. Anyway can go to bed happy now as this was my main rig and I started thinking about what if I needed new Mobo, CPU, GPU, PSU that would cost me. I was earthing myself on the radiator pipe every 5 mins or so, think I'll be digging out the antistatic band tomorrow!

More likely an exposed live wire on one of the cables touched the case. The 3pin extensions with the exposed pins are the most regular offenders for me.

I think that maybe you should just leave the PC off while your working on it, I suspect the short came from inside the PC and not your earthing.

Hawker

Some cheaper PSU's and hardware come with some rather risky molex connectors. I've seen plugs where the live metal socket (inside the plug) actually falls out making everything around it live.

Just shows you get what you pay for!

lol, reminds me when I tried to make an LED system for my old computer, by stripping one of the molex wires, and soldering some other wires to a PCB onto it, then the LED's were connected to the PCB. When if failed, I thought that there was something wrong with the PCB, so decided to use a handy peace of solder to skip the connections to the LED's, and shorted the whole thing.

Is it possible to make the entire case live by shorting something?

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Originally Posted by smargh

More likely an exposed live wire on one of the cables touched the case. The 3pin extensions with the exposed pins are the most regular offenders for me.

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Sounds like it, it came from a 3 pin fan splitter, scared the bejesus out of me:)

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Originally Posted by alex98uk

Is it possible to make the entire case live by shorting something?

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Not for long, current overflow protection will kick in sharpish (like with showers...)

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Originally Posted by TAKTAK

Not for long, current overflow protection will kick is sharpish (like with showers...)

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Yeah, and "not for long" is less than a millisecond, not even long enough for you to get a jolt from it. The chassis is grounded to the PSU to ensure a short blows a fuse (on old PSUs) or trips the PSUs breaker.

Or if you have RCDs they should blow since the case should be grounded. An RCD works by tripping if current sent out on live doesn't return on neutral, basically so if current is diverted to ground (the case) the RCD should trip.

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Originally Posted by alex98uk

Is it possible to make the entire case live by shorting something?

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Depends what you mean by 'live'. If you mean live in the sense that it is at mains potential, then that would be extremely difficult. Not only are all the outputs from the PSU isolated from the mains supply by the internal transformer, but the case will be earthed through the chassis of the PSU and possibly via a separate earth wire. In that case in the unlikely event of a component in the PSU failing, and connecting mains live to the chassis, the fault current will blow either an internal fuse in the PSU and/or the plug top fuse (probably accompanied by a bang!

The negative side of the PSU output may be connected to ground (likely) or it could be floating (very unlikely). If the former, then any of the 3, 5 or 12 volt rails touching the case will cause a short and should (on a good quality PSU) cause it to shut down safely. If the output is floating, then either of the rails may touch the case without problem. 12 volts is not a dangerous voltage.