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Rack PDU questions

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Rack PDU questions

  • Hi,
    I am in the process of reviewing how power is delivered and distributed to a few racks holding servers.
    Each have 1 Dell (supplied with rack) PDU with 11 C13 plugs on the front and a 16Amp C19 plug to go back to a UPS. This is full and previous people have used a variety of means to supply additional power from cable tied-to-rack extension leads to multiple cables running to other UPS in a different rack.

    I am hoping to reduce the number of racks by moving servers to spare space in existing racks, but this is going to put additional strain on the power distribution we have.

    What is the best way forward? I quite like the idea in http://www.dell.com/downloads/global/products/pedge/en/rapidpower_bestpractices.doc (page 24) of having 4x 16Amp PDUs on each the side of the rack which I can then wire back to a central UPS.

    I have a mixture of 1 and 2U servers all with dual PSUs, so need to be able to plug approx 38 PSU in a full rack, plus about 6 for misc equipment (KVMs, switches etc).

    I don't know whether Dell sells these PDUs seperatly as i cannot see them anywhere on their website for sale, the alternative is APC equipment, but their full-height PDUs only have a max of 20 C13s and a couple of C20s. Do these APC PDUs even fit into a standard Dell rack (42U older style rather than the shiny new ones)

    I only have single phase supply with servers currently pulling on average probably about 200 Watts each

    What would you suggest?
  • We have a pair of APC Smart-UPS 2200 at the base of each rack - each has 8 C13s + 1 C20 (for PDU) - their rack rails fit our old 4210s fine. Hopefully the bigger APC models you mention would fit just as well. Just don't start up all your servers at the same moment - the power draw might overload the APC units, requiring a reset!
    We also have some racks with UPS from an external cabinet - 2 supplies to each rack, each supply powering 2 standard PDUs (so 4 PDUs in a rack). That's fine - and we power each server from separate PDUs on different supplies (just in case!). The only improvement I can think of is to use intelligent PDUs that you can manage (power-off/on etc) via latest Dell Remote Console software.
    Hope that helps.
  • Dell/Avocent PDUs are on Dell website Shop (under Surge Protection etc) at

    Looks like the intelligent ones are the Avocent Direct models also listed. Avocent stuff is pretty good - Dell rebadge their remote switch consoles.

    BTW, I think the standard Dell PDU (11 C13s) has 2 extra C13s at the back.But when fitted in the side of a rack one or both of the rear outlets may be fouled by the structure.
  • Depending on the PDU you are using this UPS works great for 208V. We run both our datacenters with l6-20 inputs which is 208V 20A plugs to a big UPS/Genset. So if we need a standalone UPS for a rack we buy from Dell the APC Smart-UPS XL 3000VA 208V Tower/Rack Convertible UPS. This is the only unit that has two l6-20 output plugs with a L6-20 input plug. It also has two L6-30 output plugs in case you have 30A pdus. Beware you will only be able to use 20A total output as you are limited to the input which is 20A. It keeps all of our PDU compatiable in case we want to move the rack to the generator.
    Another thing to think about with your rack configration. I learned the hard way but make sure you have ample AC to cool a high density rack configuration. I built a few racks and had to remove some of the servers because our AC could not cool the rack. Your servers temps will increase a lot in a high density configuration. Good luck in your consolidation. It's a pain to cleanup but we have to keep it neat.