Consider the statistical side of the above picture. If each of those power extenders has a certain chance of failing in the coming year, how do you calculate the chance that one of them will? I'm not going to ask the probability of 1 or more failing: They're all hooked together, so if one fails then the circuit is cut.
Obviously you cannot simply add the probabilities, because that could come to a probability greater than one.
What if we assume a binomial distribution? The rules for that are short and simple, laid out in every book on it. Suppose the probability of one failing over the coming year is P(x). Then could we just call it probability of 1 failure in 6 trials at probability P(x)? If so then the formula to calculate would be Combination(6,1) * P(x)^6 * (1-P(x))^(6-1).
Therefore: if the probability of one of those failing in the coming year is .4 (a good guess I think) then the probability that one of them fails (out of all six) is: 6 * (.4 ^ 6) ( 1 - .4 )^(6-1) = 0.001 Extremely low.
Hence no doubt everything will be just fine. The more you hook together the more reliable the setup.