[Discuss] Server Room Power

[tmetro-blu at vl.com (Tom Metro)]

Matt Shields wrote:
> 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...

I gather there is a point in the power feed where you can access the hot
conductor separately from the neutral?

Others may not be aware that you can't just put the clamp over the power
cord to the server. If you do that the electromagnetic field in the two
conductors cancel each other out. You would typically need to unplug the
device and plug it in through a line separator, like:
http://www.mouser.com/ProductDetail/Extech/480172/?qs=sGAEpiMZZMvxDRaL6U%2fGjYgmQwn6WPwUnwCdDDtlhA4%3d

which separates the two conductors and lets you put a clamp over either
one individually.


Edward Ned Harvey wrote:
> ...when you wrap the clamp around two wires together, in order to
> measure the power of both combined...

Are you talking abut pairing up the hot conductors from a pair of
redundant power supplies, or are you talking about the power cords?

If the latter, see above.


> It's important to ensure both wires are connected to the same
> power source. ...they're not necessarily in-phase with each
> other.

If the former, and you're using a true RMS meter, I wouldn't expect it
would matter whether to two current waveforms are in sync. The meter
would just see it as a waveform distortion, and should still give you
the RMS power.

 -Tom

-- 
Tom Metro
Venture Logic, Newton, MA, USA
"Enterprise solutions through open source."
Professional Profile: http://tmetro.venturelogic.com/