Staggered proof test

Use staggered proof testing to reduce chances of common cause failure... 

The equations in Tables 5.1—5.6 assume that, at every proof test, all the elements are tested at the same time. An alternative method of testing is to stagger the test of each redundant element. Assume, for a two-element redundant system, that element A starts new at time equal zero, runs for half the normal proof-test period, then a proof test is completed on element B, then after a further half of the normal proof-test period element A is tested, and so on. 

Is maintenance of diverse/redundant channels staggered at such an interval as to ensure that any proof tests and cross-checks operate satisfaetorily between the maintenance ... 

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