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We have bought a few 30amp 208v PDUs that only have 9 receptacles. The servers we are connecting to those PDUs will not use the full 30amps (at 80%, or actually 40% since we use redundant power) so we need to find a way to connect more than 9 servers to the same 9 receptacles so we'll be not wasting capacity that we pay for.

I thought about using a Y split cable like this one: http://www.cablesandkits.com/power-cord-c14-c13-splitter-cable-awg-p-515.html

That will let me connect two servers to a single receptacle.

Each of the individual receptacles can provide 12 amps of power and individual servers are unlikely to consume more than 3 amps at maximal load so it should provide sufficient power.

The question is if there is any other reason why this may be a bad idea and if there is any other solution other than buying PDUs with more receptacles (which I don't want to do because I must use horizontal PDU on these racks and ones with more receptacles consume more U space).

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1 Answer 1

In general, the problems you encounter with these are much the same as you do with double adapters and power boards in your home. Some problems you'll possibly encounter:

  • Doing power maintenance can get "interesting";
  • Routing the cables is more fiddly and hard to get neat;
  • Governmental or facility regulations may prohibit the use of such things on safety grounds;
  • Managed power rails (remote switched or metered) lose quite a bit of their utility.

For myself, I wouldn't use 'em ever again, but that's largely because the company I work for sees the benefit in forking out the extra money on two or four 0RU remote-switched power rails for everything, so having power ports available is rarely, if ever, a problem. These days, having enough amps available is more of a concern than physical space in the environments I work in.

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Here's why wer'e using horizontal PDU on these racks instead of the 0RU ones we use everywhere else. Those racks have SuperMicro "twin servers" installed in them, these are 2U enclosures with 4 servers in each that you can hot-swap from the back of the rack. The problem is that the 0RU PDUs get in the way of these hot-swappable servers and we have to take out the whole enclosure to replace a single server. Therefore we had no choice but switching to horizontal PDUs. –  sagi Apr 1 '12 at 1:05
    
I'm surprised that power density isn't your limiting factor, if you've got 4 machines per 2RU of space. –  womble Apr 1 '12 at 1:48
    
Power density is a limiting factor. We're not able to nearly fill our 48U rack with those machines although we get 60amp/208v of redundant power to each rack. However, we still are able to utilize more than we can get from the 18 receptacles that the 2 x horizontal PDUs can give us. Therefore I wanted to use the Y cables to connect some of the less power intensive equipment that's installed on the rack (i.e. the access switches and some standard 1U servers) to get a few extra receptacles. –  sagi Apr 1 '12 at 2:21
    
If I had any spare RUs, I'd use PDUs over splitter cables. The splitters would be my choice of absolute last resort. –  womble Apr 1 '12 at 2:27

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