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