Dual Power Paths: A Crucial Element in a High-Availability Data Center

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Protecting your data center against power failure is crucial to providing maximum availability.  But the job entails more than simply having a backup power source, such as a generator.  You also need to protect against the failure of individual power supplies.

In high availability environments, a common way to provide redundancy is to supply two independent power paths to each piece of computing equipment. The equipment accepts the two power feeds via independent, parallel power supplies that are sized such that the equipment will continue to operate with only one power path. This system provides the following advantages:

  • If a power supply fails, the system continues to operate
  • If one power feed fails due to equipment malfunction, the system continues to operate
  • If one power feed fails due to user error the system continues to operate
  • If the power supply fails in a way which faults the power feed and trips the breakers, the equipment sharing the breaker is not affected.
  • If one power feed needs to be shut down for maintenance or upgrade, the system continues to operate

For this approach to be effective, you’ve got to meet two requirements:

  1. The protected equipment must support dual power feeds and operate with one feed faulted.
  2. The loading of breakers within each power path must always be less than 50% of trip rating during normal conditions, so the breaker doesn’t trip if the alternate path has to take on the full load. This also helps prevent tripping of the alternate path due to low line voltage conditions.

Meeting these two requirements can be a challenge. Some computing equipment is only available with a single power cord while other equipment has three power cords, where any two are needed for proper operation.  Neither type can operate with the loss of one power feed.

In such cases you can use an Automatic Transfer Switch (ATS), which generates a single feed from two inputs. An ATS may be deployed centrally or in a distributed manner, with rack-mounted ATSs placed in the rack enclosure with the protected equipment.

An adaptable rack enclosure power system would be able to support a single or dual path environment or a hybrid of both single and dual equipment. You’ll need to monitor the current to ensure that all circuits are loaded below 50% capacity in order to prevent breaker tripping during a loss of one power path.

To learn more about how to provide consistent, reliable power to your data center, check out the APC by Schneider Electric white paper, “Rack Powering Options for High Density.”

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