HE.net, Fremont-2 outage?

Joe Greco jgreco at ns.sol.net
Wed Nov 4 12:54:49 CST 2009


> Joe Greco wrote:
> > 
> > With power:
> > 
> > N+1 is usually better than N
> > Best to assume full load when doing math
> > Things will go wrong, predict common failures
> > The best plans are still prone to failure
> > Safety margins can save your rear
> > etc
> 
> I find that electrical panelboards, busways, transfer switches, etc. are
> often put in the category of things that don't need maintenance or
> routine inspections. Big deal if you can start your fancy generator once
> a month (I prefer on-load weekly) but the in between stuff is in
> disrepair or full of mice. Even a simple dusty transfer switch could arc
> weld itself to once side of the contacts.

Yup.  Related: "100% availability" is a marketing person's dream; it 
sounds good in theory but is unattainable in practice, and is a reliable
sign of non-100%-reliability.

The most common way to gain "100% availability" is to avoid testing
under load.  This surely protects the equipment against a whole slew of
failures in the less-used portions of your power systems, but also
protects you from detecting them outside your Hour(s) Of Greatest Need.

And even for those who follow best practices...  You can inspect and 
maintain things until you're blue in the face.  One day a contractor 
will drop a wrench into a PDU or UPS or whatever and spectacular things
will happen.  Or a battery develops a strange fault.

You do live load testing, you'll lose now and then.  It's best to simply
assume no single circuit is 100% reliable.  You should be able to get
two circuits from separate power systems and the combination of the two
should really closely approximate 100%, but even there...  it isn't.

... JG
-- 
Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.




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