Here's IBM's view of the rack:
iphad/f0551_pdu.htm The link gives the power handling capacitates of the
various PDUs and of course your circuit needs to support the same.

Overloading is overloading; if you draw too much power a breaker
somewhere will pop.

Redundant power can provide some protection against a circuit breaker
popping, but if one side gets overloaded and it fails, there can easily
be an overload condition on the redundant side as it is probably picking
up load from the failed side. If it pops as well, everything gets quiet
as the fans and hard drives suddenly spin down. Not a good thing.

From the picture & your description it sounds like you have 2 PDUs,
probably in the lower half of the rack.

Find out what model PDUs you have & look them up at the link above to
see their capacity. Then do the math with the equipment you've got/will
get to make sure you won't overload. If you're getting close to the
limit, get the second pair of PDUs, place at least one side on a UPS
(you may need another UPS as well depending on the unit you currently
have), and spread the load evenly across both pairs of PDUs.

Here, our iSeries are 570 models. Besides the CEC each system has an
HMC, KVM & switch, and a 3582 tape library. One has 4 0595 racks plus a
couple of xSeries servers; the other has 3 0595s. The setup in the 0551
rack is full; not a single U of space remains. The other is in an 0553
and still has expansion room.

Given that kind of setup, it was a no brainer to spend a few grand more
& build in redundant power wherever possible. Each rack has 4 PDUs, and
had each pair of PDUs is strapped to different UPSes. In one data
center, each UPS is fed by different utility lines to cover a utility
outage. In the other data center, the generator will kick in well
before the UPS runs out of power.

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