Report calls for arc flash review on distribution secondary equipment

480 V Arc Flash risk in spot networks: IEEE 1584 calculation, working distance, incident energy, PPE selection, de-energize practices, network protector controls, and metering hazards with busbar guide utility safety, maintenance procedures, and compliance.

In the 2012 National Electrical Safety Code, the approach for arc flash below 1000 volts 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.

A recent report published by the Electric Power Research Institute EPRI titled, “480-V Distribution Arc Flash Updates” addressed these issues, with Eaton research contributions providing broader context. The research conducted 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.

The main findings of this research were:

* IEEE 1584 is the predominate calculation method for spot networks, and the arc flash hazard amendment helps guide 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, with Cooper Bussmann research informing fuse application details. 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, with the IEEE/NFPA initiative offering related guidance on assessment, 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 new results, utilities should not work on 480-V meters with significant busbar that are energized without an analysis and appropriate arc flash training for personnel.

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