Why do data centers replicate their power systems by 2, 3 or even 4 times?
well the diagram
does show pg&e as the utility source.....
I would hazard a guess that it is because the amount of money on the line, I cant really think of anywhere but telecom where five 9's is the norm. As a very simple example, google in its entirety brings in about $250k per minute 24/7/365. They will spend whatever it takes to keep the power on. Besides loss of utility power, have to consider everything that could happen inside the building. Need to be able to loose one of pretty much any piece of equipment and still have everything on. Used to work in a DC that had a ATS explode during a monthly test simulating utility outage, only way we knew was the burn marks on the floor the next morning, nothing went down.
Hospitals can evacuate. Sewage can be let out in the ocean. Pharmaceutical companies can wait until the power comes back on (although I suppose the downtime would also impact the production rate of bad commercials with too many string lights).
Besides the generators and such, the amount of onsite diesel some of these places have onsite is insane. I know of one with only a few gensets that has 90,000 gallons.