[BBLISA] PDU Power Ratings?

[John P. Rouillard]

Hi Rich:


In message <1722c270.1ER.1lD.1b.7KiSop at mailjet.com>,
"Rich Braun" writes:

>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).

Ummm, how does that work exactly. Max continual load on any pdu is 80%
of the circuit. So for a 20 amp circuit, you can have a max continuous
load of 16 amps.

Now if devices D1...DN have dual plugs and one goes to pdu P1 and the
other goes to pdu P2, each pdu will see 1/2 the amperage load of the
devices. If the pdu's (P1, P2) are each on a 20 amp circuit, I claim
the max continuous current on each pdu is 8-9 amps or 1/2 of the
continuous circuit capacity.

If that isn't done what happens if the P1 breaker trips? The 1/2 of
the load being borne by P1 now is pulled from P2 which means P2 now
has a 16/18 Amp load, which is within its 20 amp capacity and your
equipment stays up.

If as you claim I use 12/13 amps on each pdu then when P1 fails I load
P2 with 24+ amps. This should trip the breaker supplying P2 since that
is not just a surge load for a few milliseconds but the new continuous
load.

What am I missing in your argument?

--
				-- rouilj
John Rouillard
===========================================================================
My employers don't acknowledge my existence much less my opinions.