How does the parallel redundant UPS configuration differ from an isolated redundant UPS configuration?

Question

Options

• AA parallel redundant configuration is considered N+1 and an isolated redundant configuration is considered 2N.
• BA parallel redundant configuration requires a static bypass switch and an isolated redundant configuration does not.
• CA parallel redundant configuration eliminates downstream single points of failure and an isolated redundant configuration does not.
• DA parallel redundant configuration requires models of the same capacity from the same manufacturer and isolated redundant does not.

• A
  14% (9)
• B
  3% (2)
• C
  8% (5)
• D
  75% (47)

Explanation

Option D is correct because parallel redundant UPS units operate on a shared bus, meaning all units must carry equal portions of the load simultaneously - this requires identical capacity ratings and typically the same manufacturer to ensure compatible load-sharing behavior. Isolated redundant configurations use completely independent UPS systems feeding separate distribution paths, so the units do not need to share load and can therefore differ in capacity or manufacturer.

Option A is wrong because the N+1 versus 2N distinction describes redundancy levels, not topology types - a parallel redundant system can be 2N, and the classification does not reliably distinguish between these two configurations. Option B is wrong because both configuration types can include a static bypass switch; it is not a feature exclusive to parallel redundant designs. Option C has the relationship backwards: it is the isolated redundant configuration that better eliminates downstream single points of failure, since each UPS feeds a completely separate distribution path, whereas a parallel redundant system shares a common output bus that can itself be a single point of failure.

Memory tip: "Parallel means matched" - parallel units work together on a shared bus, so they must be identical; isolated units work alone on separate paths, so they can be mixed.

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