Somewhat OT - can underpowered power supplies damage a system?

James Mckenzie jjmckenzie51 at
Wed Aug 18 21:18:46 UTC 2010

suvayu ali <fatkasuvayu+linux at> wrote:
>Sent: Aug 18, 2010 1:31 PM
>To: James Mckenzie <jjmckenzie51 at>, Community support for Fedora users <users at>
>Subject: Re: Somewhat OT - can underpowered power supplies damage a system?
>On 18 August 2010 09:08, James Mckenzie <jjmckenzie51 at> wrote:
>> Maybe a brand name's power supply would have not shorted out, but then the mobo, drives and everything else
>>would have received a 6000 volt shock.  And yes, the UPS was brand name (highly rated BTW) but the short duration
>>was so short that the system did not shut down.
>I think you are concluding incorrectly. A well made PSU ideally would
>have blown the fuse, and saved both your PSU and your hardware. You
>would only need to replace the PSU fuse to get back up and running. At
>least that is my understanding.
What I'm describing is a Primary (6000/7200/13800) to Secondary (220) transformer short.  This means that the 220 lines for a short duration was carrying the primary voltage.  Yes, the fuse should have blown, but in my case the fuse blew such velocity, the wire was splattered on the glass casing.  The internal transformer shorted out due to the amount of current carried for that moment.  Replacing the fuse resulted in another splatter and what looked like an arc over.  In most countries there are load limiters placed on the secondary side that prevent primary voltage from reaching your home (ever wonder what those things on the power pole were.)  Where I was living at the time did not have these and a surge on the primary side caused the short.  Was interesting to see a ground mounted transformer to this.  This can also happen to an oil cooled transformer if it overheats and the coolant is released (usually, the secondary side is also disconnected when this happens.)

However, a really good UPS/PSU combination with an EXCELLENT ground will drain off the overvoltage and the PSU will never see the overvoltage.  PSU's with blockers will also capture any overvoltage and drain it through the earth ground.

This is why data centers use different UPS configurations than you have at home and industrial standards require less than .5 ohm (in some cases way less) to earth ground.  There is an entire industry build around this.  Most homes have 'open' grounds and the people in them are not aware.  I've got to fix the ground in the house I live in as the power strip I use is compaining of one.

James McKenzie

>Open source is the future. It sets us free.

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