Somewhat OT - can underpowered power supplies damage a system?

Gene Heskett gene.heskett at
Wed Aug 18 23:04:16 UTC 2010

On Wednesday, August 18, 2010 06:49:35 pm James Mckenzie did opine:

> 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> 
> >> 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

While the addition of such a power company side of the meter surge 
protection might seem like a great idea, and should be mandated by such as 
the UL, the fact is that its an expensive thing to do, and is generally 
left to the user to implement.  Go right ahead and do it, UL approved 
starter kits for the 250 (127-0-127) common US household supply will cost 
you about 2 grand & 10% of that to get it installed, IF (note caps) you can 
find an electrician who truly understands the requirements AND (note caps) 
your existing grounding system at the meterhead is suitable.  There is a 
lot of grandfathered stuff, probably 75% of which doesn't pass the test when 
mother nature decides you aren't supposed to call that stuff butter.

As James says, not many are.  I did bring mine up to specs when I replaced 
the original 60 amp service with a 200 several years ago.  Here in my man 
cave, everything but the lights and a huge wall wart for the audio runs 
from a single, checked out wall plug, into which a huge surge arrestor is 
plugged, and the only thing not directly connected is the recently 
installed cable modem, everything else is on this surge protector or on a 
1500WA UPS plugged into that surge protector.  We have had tonnes of nearby 
strikes since I did that, but generally, if a strike gets in, that surge 
protector see's to it that everything in the room bounces in unison.  The 
net result is that I have not lost a single piece of electronics under this 
umbrella in a bit over a decade.

Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Hello.  I know the divorce rate among unmarried Catholic Alaskan females!!

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