[unbalancedevh]

I found this statement to be confusing (the bolded part):

> Moreover, because the two ground circuits are mutually independent, no single failure can cause both grounds to fail. *This lowers the probability of a ground failure*: If the probability of a single ground failure is P, the probability of both failing is P2.

If there are 2 independent systems with the same failure modes, the probability of a single failure goes up. The probability that both fail is lower -- but I'm not sure what they mean by "P2." I'm pretty sure it isn't "P squared", if that's what they're implying, since if one succumbs to a failure mode that's shared by both, then it's somewhat more likely that the second will also fail.

I think, though, that by "probability of a ground failure" they're not referring to any ground failure, which unfortunately still renders the system inoperable; they're referring to a complete lack of ground connection, such that the system would be unsafe.