T&D World Magazine

EPRI Publishes 480-V Distribution Arc Flash Updates

In the 2012 National Electrical Safety Code, the approach for arc flash below 1,000 V has changed. Now, utilities will have to review arc flash on distribution secondary equipment. The two main changes are at 480 V for metering and spot networks. To address these issues, EPRI research in 2011 concentrated on 480-V arc flash. For 480-V spot networks, research concentrated on information exchange and practices to manage arc flash in spot networks. EPRI has released the main findings of this research:

  • IEEE 1584 is the predominate calculation method for spot networks with utilities assuming either an 18- or 24-inch (45.7- or 61.0-cm) working distance.

  • Many utilities are de-energizing the feeder for spot network work. This reduces fault current and energized buswork in protectors. Note that they are not operating a primary-side oil switch.

  • Work is manageable in many spot networks with heavy arc suits (100 cal/cm2 suits are common).

  • Utilities normally assume either a self-extraction time or assume that internal network protector fuses operate. Both assumptions allow work in many spot networks with available arc flash suits. Both assumptions also have disadvantages.

  • External fuses or disconnects are a promising option to reduce incident energies and completely de-energize a network protector. These scenarios can be treated as open-air applications if the only exposure is line to ground.

For 480-V metering, several exploratory tests were performed on different meter styles to see if there were any units where the 20 cal/cm2 threshold would not apply. Tests showed that meters with significant internal busbar can have long durations and incident energies much higher than 20 cal/cm2.

Based on these results, utilities should not work on 480-V meters with significant busbar that are energized without an analysis.

For more information, visit www.epri.com.

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