nanog mailing list archives

RE: Want to move to all 208V for server racks


From: Alex Rubenstein <alex () corp nac net>
Date: Fri, 3 Dec 2010 13:23:49 -0500

btw, one thing I do not recall seeing on this thread is that 208v avoids one of
the common problems with 120v, which is the third harmonic issue.

With the cheaper switching power supplies, one will often see significant 3rd
harmonics in the waveforms(*).  The 3rd harmonic, across a 3 phase circuit,
are additive on the neutral.  In worst case, your (common) neutral current
may exceed the line currents.  Proper engineering for significant 120v
distribution in new DC construction often requires double sized neutrals to
mitigate against this.
Using 208v mitigates this particular issue.

I should have been clearer, when I originally said, "it lessens neutral currents." I meant that to mean, as well, less 
harmonics.




Current thread: