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

[Ingo Flaschberger <if () xip at>]

Dear Leo,

> 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.

currents above 1mA and 50V are dangerous.
also the net-frequency of 50hz/60hz cause troubles for the heart 
(Ventricular fibrillation).

If a really fail-tolerant system is needed, that the only solution if to 
have a ground-free system. the incomming power is transformed (1:1 for 
example) and not earthed.
a special device monitors the voltage between earth and power and do an 
alarm if one of the power-lines connects to earth - but do no shutdown.
the fault can then be repaired without shutdowns.
only when 2 faults occur the breakers trip.
usually hospitals use such a configuration.

probably hilkar system is similar to this one.

Kind regards,
        Ingo Flaschberger