An arc flash study can be a bit complicated if you are new to this field. Knowing where to begin, what to include, how far to go, how to use the software etc. can seem like an insurmountable undertaking. WORSE – you are going to contract the study and don’t know what to ask for. The good news, there are many well qualified consultants that can help guide you through the process. The bad news – there are plenty of people ready to take advantage of the situation once they realize this might be your first study.
An arc flash study is not suppose to be thought of as simply an item that needs “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 can be a dangerous view 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 made , or equipment that should have been included was missed or ignored. 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 fully understand what is involved in an arc flash study.
In an attempt to assist people specify an arc flash study, the IEEE 1584 working group developed a new standard that was published earlier the year. The title of this new standard is:
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 understand 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 the Study
One of the first considerations should be about 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, the study should be reviewed by a more experienced person.
Another consideration is some state engineering licensing boards may consider an arc flash study as an engineering service. This may require that 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 included….” is another frequent comment 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 and / 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 at a minimum will 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 are very out of date or have never been performed, the specification will need to address whether the short circuit study is only used for determining short circuit current for the arc flash study or should it also include reviewing equipment adequacy. Similarly, are the results of a coordination study only used to determine the arcing current duration at each location in the study or should recommendations also be made for improving coordination and/or reducing the incident energy?
It is a long list
The list of items that need to be considered as part of the arc flash study is quite long. 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.