[Discuss] Server Room Power

[Edward Ned Harvey]

> From: Matt Shields [mailto:matt at mattshields.org]
> 
> I also have a killawatt but the problem comes when I have to work on
> someone else's live equipment.  The clampon ammeter means I don't have
> to shut the server's off. I can also clamp on to the rack's main power
feed if I
> don't have a APC PDU.  Well worth the money I spent.

If you have redundant power supplies, you just unplug one at a time, no need
to shut off just because you're measuring with a kill-a-watt.  But yeah, if
you don't have redundant power supply on the server in question...  The need
to shutdown certainly stinks.

But I certainly agree, the clamp is the most convenient.  BTW, when you wrap
the clamp around two wires together, in order to measure the power of both
combined...  It's important to ensure both wires are connected to the same
power source.  Because (for example) if one's plugged into the wall and the
other plugged into a UPS, then they're not necessarily in-phase with each
other.  They can sort-of cancel each other out somewhat, and produce a false
low reading.