stacking pdu

Sat May 30 01:34:06 UTC 2015

> On May 29, 2015, at 2:48 PM, Brandon Martin <lists.nanog at monmotha.net> wrote:
> 
> On 05/29/2015 05:29 PM, William Herrin wrote:
>> On Fri, May 29, 2015 at 4:32 PM, shawn wilson <ag4ve.us at gmail.com> wrote:
>>> Is there a way to stack PDUs? like, with 30A 220, we need more plugs
>>> than power but I'd like them to communicate to make sure we don't over
>>> power the circuit. Do any APC or Triplite systems support this?
>> 
>> Isn't it against the NEC and the fire code to stack power strips? We
>> all do it, but isn't it against code?
> 
> It sounds like he's asking for a PDU specifically intended to be used with managed expansion/stacking type modules.  That would be permissible per NEC and most local fire codes as the device would be specifically listed for such usage.  I've seen something like this inside blade/modular racks like IBM Flex systems, but unfortunately I don't know of any such off-the-shelf parts.
> 
> It would seem entirely reasonable to take a 30A/240V feed on a 6-30 or 14-30 type connection and break it out to numerous either C13 or 6-15/5-15 style sockets, possibly on a modular basis using some sort of proprietary power+data connections for the breakout.  E.g. if you needed to mix 120V and 240V devices in a rack, you could get 5-15 and 6-15 breakouts with each individual outlet switched and maintain whole-rack metering.
> 
> Sounds like a really handy device, if one exists COTS.
> -- 
> Brandon Martin

If I read it correctly, stacking PDUs is perfectly acceptable so long as the breaker feeding each subordinate PDU is sized no larger than the maximum current that can be safely delivered to that PDU.

However, adding extension cords or other “temporary power extenders” on a permanent basis is also unacceptable and most PDU stacking of the type being contemplated here involves deploying the subordinate PDU in a way that ends up being essentially an “extension cord” for this purpose.

Owen