Effect of isolated grounding
In a large office complex, computer errors including system crashes/reboots were happening during thunderstorms. The grounding of computer system had been carried out according to the recommendations of manufacturers.
The grounding leads were insulated and terminated to an isolated grounding bus. This bus was connected to a grounding electrode consisting of multiple driven rods well away from the building.
It was suspected that the isolated computer grounding system was responsible for this problem. Measurements were made using a power quality monitor to confirm this.
This presented a safety hazard to personnel using these computer systems and was also introducing noise into the systems through the capacitances between the computer systems and the building ground (refer Figure 1).
Note: Lightning current flowing through the lightning conductor to ground electrodes causes the potential of the building members to rise above that of the causing system errors. Unsafe potentials can also arise.
The manufacturer of the computer systems was consulted and the computer ground system and the building ground were bonded together on a trial basis.
It was noticed that the system problems were no longer occurring. The grounding wires of computer systems were also routed along with the power supply wires to the systems for better performance.
Reference: Practical Grounding, Bonding, Shielding and Surge Protection – G. Vijayaraghavan, Mark Brown, Malcolm Barnes (Purchase it from Amazon)