[AusNOG] Bottom of rack UPS

[Damien Gardner Jnr]

On 16/12/2010, at 6:43 PM, John Edwards wrote:

> This gives you a race condition that is not easily resolved at a time when remote hands are probably at their busiest!
> 
> For the home electricians, this is also the number two reason why you shouldn't hack a standard power plug onto the cable that comes with a 3KVA or bigger UPS...

Not to mention the absolute fit the RCD on your house supply will have when the fairly beefy tri-star cap arrangement on the input to the UPS charges up..  Fitting a 3KVA UPS in a house is actually bloody tricky these days - you can't add a new circuit with power points which is NOT on an RCD... but you can't put your UPS  *ON* an RCD, and be sure it won't trip even with a brownout, let alone a full blackout...  Heck, it can be an issue in an office too - I have a few clients who have ended up having to modify their their APC 3KVA rackmount UPS's for hardwired input, because they couldn't get an exemption from the requirement to have an RCD on all power outlets, even for their dedicated 15A outlets in their server room..

I was lucky in our current everything-RCD'd house, in that when the meter box was re-wired a few years ago to add an RCD to the power point circuits, the electrician neglected to move the fridge circuit over (Don't ask me why there's a 32A breaker running to a *single* 15A outlet behind our fridge in the kitchen, I sure as heck don't know!  But it was a good thing (TM) for me)  as I now have a nice long 15A extension cable running from there to the office to run the UPS ;)  The myriad of little 1kva units spread around the house don't seem to cause a problem, but the 'big' (ever tried lifting one of those suckers into the top of a rack, even sans-batteries?) unit is guaranteed to trip the RCD *every* time we have a brownout..  There's a reason I look in the fusebox of every house we look at while house-shopping.. I'm looking for the nice old faithful ceramic fuse holders and lack of RCD ;)

*grin* and I'm assuming your unstated #1 reason not to hack a standard power plug on, is because it's illegal (quals and licensing aside even, you can't run a 15A device from a 10A outlet..)? ;)

--DG

Damien Gardner Jnr
VK2TDG. Dip EE. GradIEAust
rendrag at rendrag.net -  http://www.rendrag.net/
--
We rode on the winds of the rising storm,
 We ran to the sounds of thunder.
We danced among the lightning bolts,
 and tore the world asunder

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