[133109] in North American Network Operators' Group
Re: Want to move to all 208V for server racks
daemon@ATHENA.MIT.EDU (Robert Bonomi)
Sat Dec 4 18:50:03 2010
Date: Sat, 4 Dec 2010 17:47:29 -0600 (CST)
From: Robert Bonomi <bonomi@mail.r-bonomi.com>
To: bicknell@ufp.org, nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
> Date: Fri, 3 Dec 2010 09:42:10 -0800
> From: Leo Bicknell <bicknell@ufp.org>
> Subject: Re: Want to move to all 208V for server racks
>
> In a message written on Fri, Dec 03, 2010 at 04:57:03PM +0000, Gary Buhrmas=
> ter wrote:
> > limits so that ones life has increased protection. A protective trip
> > is better than
> > the alternative.
>
> Not always.
>
> I worked in a data center with something I thought was very, very cool.
>
> http://www.hilkar.com/highresistance.htm
>
> The concept, at a high level, is rather than tie the (service, not
> signal) ground back to grounding rods directly you run it through a
> large resistor. Now when a phase is "grounded" it runs through the
> resistor, allowing a small but safe current to flow.
>
> Why is this cool? Well, say you have a power strip running at 10A
> with a bunch of servers on it. If you took a paperclip and inserted it
> in an empty plug connecting hot to ground with a normal system
> (simulating a faulty bit of gear) the breaker would trip, all your
> servers would go off.
>
> If you did this with a high resistance setup the paperclip would conduct
> about 0.5A, maybe less. An alarm, dectecting current, at the resistor
> would go off to say there was a fault. Your circuit would draw 10.5
> amps and everything would stay up and running. That faulty bit of gear
> didn't take down your entire power strip.
>
> This totally eliminates arc faults, and there isn't enough current to
> ground to arc. I think GFCI's are also unnecessary, as the fault can't
> conduct enough current to be harmful.
All is "well and good", *UNTIL* "something happens" that introduces _another_
path to 'ground' that bypasses the 'high rresistance' links.
(Reminiscent of the old "Branch on C.E. grounded" programming joke.)
