Specifying Arc-flash Studies - IEEE 1584.1
Published: November 2014
By Jim Phillips
An arc-flash study should not be thought of simply as an item that needs to be checked off the list. However, many people still view it this way. It is not unusual to hear, "I don't completely understand what an arc-flash study is, but I need one," or "Can't you just provide us with a typical study?"
This view can be a dangerous because, unlike other types of analytical studies, an arc-flash study is used to specify appropriate protection from the potentially deadly arc-flash hazard. It is about a person's safety, and mistakes could result in severe injury or worse.
It still happens. The specification for the study can be meticulously developed, and it is believed that it covers everything. Then, all too often, the phrase, "But I thought that was included in the arc-flash study," is heard.
There are many stories about arc-flash studies that were plagued with errors, incorrect assumptions, or missing or ignored equipment that should have been included. Sometimes, this can be attributed to lack of experience, or it may be a lack of understanding about exactly what the scope should be. The problem can be more frustrating when the specifier does not understand what is involved in an arc-flash study.
In an attempt to assist people specifying an arc-flash study, the IEEE 1584 working group developed a standard that was published earlier this year: "IEEE 1584.1 - IEEE Guide for the Specification of Scope and Deliverable Requirements for an Arc-Flash Hazard Calculations Study in Accordance with IEEE 1584."
"Dot One," as it is sometimes called, is not the same as the IEEE 1584 calculation standard, which is still in the revision stage. The purpose of IEEE 1584.1 is to assist people in understanding the minimum scope of work and deliverables required. The standard defines the recommended minimum guidelines for performing the arc-flash study based on IEEE Std 1584 - IEEE Guide for Performing Arc-Flash Hazard Calculations.
Qualifications for performing a study
One of the first considerations should be the qualifications of the person that will be performing the study. IEEE 1584.1 recommends that the arc-flash study should be performed by, or under the direction of, a person with experience in power system analysis and arc-flash hazard analysis. If the person performing the study has limited experience, a more experienced person should review the study.
Also, some state engineering licensing boards may consider an arc-flash study as an engineering service, which is another consideration. This may require the study be performed by or under the direction of a licensed engineer. The individual state engineering board should be contacted to determine an individual state's requirements
Scope - what to include
"But I thought you were going to include..." is also frequently heard during the review of a study. Defining what equipment should be included can be one of the more difficult parts of the specification. As a minimum, the arc-flash study should include all equipment likely to require service or inspection while energized. This encompasses customer-owned service entrance equipment down through equipment rated 208 volts. IEEE Std 1584 contains language where certain circuits may be excluded from the study, depending on the voltage and size of transformer upstream.
Years ago, I took an informal survey at www.ArcFlashForum.com and found that the overwhelming majority of people consider data collection to be more than half of the entire study effort. It can be quite an extensive undertaking.
To reduce the overall cost of the study, it may be suggested to use data from an existing short-circuit or coordination study. Although this seems like a reasonable approach, caution should be used. How up-to-date is the existing study that will be used? Even if it is considered current, the existing short-circuit and coordination studies will, at a minimum, still need to be validated for accuracy and revised to include any changes that might have occurred since it was completed.
Where a short circuit and coordination study is very out-of-date or has never been performed, the specification will need to address whether the short-circuit study only is used for determining short-circuit current for the arc-flash study or whether it should also include reviewing equipment adequacy. Similarly, are the results of a coordination study used to determine the arcing current duration at each location in the study only or should recommendations also be made for improving coordination and/or reducing the incident energy?
It is a long list
The items that need to be considered as part of the arc-flash study are numerous. Those listed here are just the tip of the iceberg. For more comprehensive guidance, IEEE 1584.1 was developed to assist in creating a more complete arc-flash study specification. Visit www.ieee.org.