[BBLISA] PDU Power Ratings?

[Rich Braun]

Scott Danek wrote:
> We have some APC PDU's in mind and we'll probably start looking into
> going 208V 20 amp in our colo.  Thanks all for your help!

That's probably the wisest move.  In addition to all the other
comments/questions, I would add this: if I make future upgrades to the colo,
will I want to scale up with 208V 20A circuits or 120V 30A ones?

I had a mix of PDUs in the past at the Savvis colo; my predecessor had bought
a lot of 120V 20A circuits, about 4 208V 20A ones, and a couple of 120V 30A
circuits.  Looking at the provider's service pricing--at that time, they had
no metering so our circuits were all billed at a rate reflecting maximum usage
at all times, except those that were denoted "backup"--I opted for the 208V
ones for all expansion.  PDUs are expensive enough that we kept all the old
ones rather than upgrading existing circuits.

One of the other issues you should address is fault-tolerance; if a breaker
pops, does your gear stay up?  I laid out the racks with color-coding across
the 3 phases (each PDU is labeled its corresponding color) and made sure each
dual-powered device was attached to two differently-colored PDUs.  This is
another argument for 208V rather than 120:  you get three phases instead of
just two.  Hence you can spread dual-powered devices in such a way that you
can use 12A to 13A of each 20A circuit rather than only 8A to 9.5A.  Exceed
those limits, and a single fault will trigger faults on the other phase(s).

Go 208V to future-proof even if you aren't dual-powered yet.

-rich