Want to move to all 208V for server racks

Thu Dec 2 21:42:45 UTC 2010

One thing to be aware of- if you are going to be connecting gear with bigger
current draws- Cisco 6509's, most blade enclosures etc. come to mind- then
many of them effectively require 208V C19 connectors.

There are not as many power strips out there that provide sufficient numbers
of C19 connectors as would be desired, particularly if you want remote
switched power.

In that case 3 Phase power becomes more attractive.  Since many datacenters
are moving towards consolidation on Blades with SAN backend storage, it is
worth keeping in mind.

In the current DC's we support, we find the only need for 120V is for
laptops and such, which is solved by "convenience outlets" that are not on
the UPS plant.  We always get at least two 120V circuits just in case they
are needed, but haven't had any requirements for them recently.

--D

On Thu, Dec 2, 2010 at 1:22 PM, Steven Bellovin <smb at cs.columbia.edu> wrote:

>
> On Dec 2, 2010, at 3:54 15PM, Jay Ashworth wrote:
>
> > ----- Original Message -----
> >> From: "Ingo Flaschberger" <if at xip.at>
> >>
> >> in europe GFIs are always needed for prection and by law.
> >> to avoid the cascading effects the GFCIs are better.
> >> break current ranges from 10mA (bath) up to 300mA; for servers I use
> >> the 30mA with pulse protection (internal delay) to avoid the server
> >> powersupply capacitor loading GFCIs "flip".
> >
> > And that, indeed, is one of the circumstances in which Chris Lewis and
> > Steve Bellovin's Wiring FAQ suggests that you should *not* use a GFCI:
> > in places where the inevitable "nuisance trip" is troublesome, like
> > powering servers.
> >
> > That FAQ is a bit dated, of course.
>
> Indeed; it's been unmaintained for quite a number of years at this point.
>
> The major place I personally have trouble with GFCIs is on things with
> big motors, and in particular my basement dehumidifier -- a place I really
> want a GFCI because we've occasionally had water problems...
> >
> > And indeed, I never liked GFCI breakers for the usages for which they're
> > mandated in the US, cause the milliamp currents they're supposed to trip
> > on are no match for all that copper resistance...
> >
> Wire resistance shouldn't matter.  A GFCI is measuring the current in the
> hot wire compared to the current in the neutral wire; if they differ by
> more
> than about 5 milliamps, the device trips.  That's why motors cause
> problems:
> the inductance of the windings can cause a brief current imbalance.
>
> Anyway -- in response to the original question: the US electrical code
> requires GFCI protection for outlets in kitchens, bathrooms, or unfinished
> basements, for outdoor outlets, and for any other outlet near water.
>  Canada
> has slightly different rules, or at least it did when we last updated the
> FAQ (Chris Lewis is Canadian): their code requires that every duplex
> kitchen outlet be served by two separate circuits, which generally share a
> common neutral.  A simple outlet GFCI can't handle that setup, since the
> actual current flowing through the neutral will vary depending on the loads
> on the two hot wires.  You'd need a specialized outlet or breaker GFCI that
> summed the current across all three wires; such devices may exist but I've
> never seen them.  (Btw -- the usual reason for using outlet GFCIs is that
> they're much cheaper than breaker versions.)
>
>
>                --Steve Bellovin, http://www.cs.columbia.edu/~smb
>
>
>
>
>
>
>

-- 
--  Darren Bolding                  --
--  darren at bolding.org           --