[gentoo-amd64] Re: What went wrong

[Duncan]

David Fellows <fellows@×××.ca> posted
200701170045.l0H0joJQ024617@××××××××××××.ca, excerpted below, on  Tue, 16
Jan 2007 20:45:49 -0400:

> Underwriters Laboratories.  They test and certify products for electrical
> and fire safety and adherence to relevant safety standards and codes. As
> far as I know they do not comment on performance.  Ie a UL listed power
> supply shouldn't electrocute you nor spontaneously combust, but there are
> no statements about how well it supplies regulated power to your
> motherboard.

Except that they do certify the supply as providing the rated wattage and
maintaining voltages under load.  The reason is that if a power supply
won't meet its ratings, only providing a sustained 250 watt when it's
rated 450 watt, if it's actually hooked to a load demanding 450 watt, it's
overloaded seriously enough to have a good chance of shorting out. 
Anybody like exploding power supplies?  What about when you are sleeping
or at work, and left the computer running?  That's a good way to lose a
house to fire, or short out hot to the exposed metal chassis for some
two-year-old kid to come across and fry themselves.  /That's/ why UL has
an interest in and rates computer power supplies, among other things.

The worst part is, a lot of cheap cases come with power supplies with
/incredibly/ inflated ratings.  That 450 watt rating but only providing
250 watt is actually not uncommon at all, in such things.  However, when
one examines said power supplies, they tend to have no recognized
certifications of any sort.  They stick some random but good sounding
rating on the side, but the things are crap and that's pretty much exactly
what it is, a random but good sounding rating.

If one always ensures they get a UL (or whatever local equivalent)
certified power supply, it certifies at least two things.

1) The power supply provides the rated voltages under the specified loads
(wattage/amperage).

2) Should some serious over-voltage or over-amperage (including
load side dead-shorts to ground) occur, the power supply will NOT fail
catastrophically. That is, it will NOT explode, shoot fire, or otherwise
become a hazard to human health and safety.  Many will blow fuses or
better yet, trigger electronic shutoffs of the shorted out leg, such that
resetting the shutoff or replacing the fuse will get you back in business,
but at worst, the device must do no more than "brick", that is, fail with
little more than the pop of critical components deliberately designed in
at the failure points, while continuing to protect human health and safety.

It should be noted what the UL does NOT do, however.  While they certify
sane operational ranges withing rating, and non-catastrophic failure
modes, they do NOT necessarily certify voltage rise times and the like
specifically suitable to computerized electronics.  It's theoretically
possible to get a UL certified power supply that simply isn't suitable to
power a computer, even tho it meets safety and specific rating
certification requirements.  However, in practice, the companies that go
to the trouble and testing expense of getting UL certified, aren't the
type of fly-by-nights that simply don't care, or they'd not have gone to
the trouble and expense in the first place.  By the time they get their
products UL certified, they are companies that have invested significant
resources into their reputations, and have no intention of blowing that,
having gone to all the expense to design and certify their product, just
to save 10 cents on a component that while not dangerous, won't provide
suitably stable computer operating power.  Thus, in practice, UL listed
means rather more than the actual certifications in the test itself, and a
UL listed power supply is with little doubt going to be a dependable
power supply, as well as physically safe.

OTOH, trust your computer to an uncertified power supply and you are very
literally gambling not only the computer's safety but your own.   Google
exploding power supplies some time, should you doubt.

Of course, that's pretty much what you said anyway, except that you didn't
note the practical effect of UL certification being a mark of quality,
because certification has by definition and process already separated out
the guys who don't care about reputation or quality and are simply out to
make some fast money, human safety or no human safety.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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