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Why do we use facilities with EPO's?

  • From: Leo Bicknell
  • Date: Wed Jul 25 14:01:21 2007

I was complaining to some of the power designers during the building
of a major facility that the EPO button represented a single point
of failure, and effectively made all of the redundancy built into
the power system useless.  After all, what's the point of having
two (or more) of anything, if there's one button somewhere that
turns it all off?

What I found interesting is that a single EPO is not a hard and
fast rule.  They walked me through a twisty maze of the national
electric code, the national fire code, and local regulations.
Through that journey, they left me with a rather interesting tidbit.

The more "urban" an area the more likely it is to have strict fire
codes.  Typically these codes require a single EPO for the entire
structure, there's no way to compartmentalize to rooms or subsystems.
However in more rural areas this is often not so, and they had in
fact built data centers to code WITHOUT a single building EPO in
several locations.  That's to say there was no EPO, but that it may
only affect a single room, or even a single device.

If they can be avoided, why do we put up with them?  Do we really
want our colo in downtown San Francisco bad enough to take the risk
of having a single point of failure?  How can we, as engineers, ask
questions about how many generators, how much fuel, and yet take
for granted that there is one button on the wall that makes it all
turn off?  Is it simply that having colo in the middle of the city
is so convenient that it overrides the increased cost and the reduced
redundancy that are necessitated by that location?

       Leo Bicknell - [email protected] - CCIE 3440
        PGP keys at
Read TMBG List - [email protected],

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