Want to move to all 208V for server racks

Robert Bonomi bonomi at mail.r-bonomi.com
Sat Dec 4 23:47:29 UTC 2010


> Date: Fri, 3 Dec 2010 09:42:10 -0800
> From: Leo Bicknell <bicknell at 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.)







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