2015 NFPA 70E Changes

The following is an article that I wrote a few years ago listing the major changes for the 2015 edition. It was originally published in the May 2014 issue of Electrical Contractor Magazine and is provided here as a resource for your use.

Change Is On The Way! 2015 NFPA 70E
Published: May 2014 – Electrical Contractor Magazine
By Jim Phillips

Deja vu?

Déjà vu is that feeling you get when you think you have seen or done something before. NFPA 70E is giving us all déjà vu since it was just three short years ago, in 2011, that we were analyzing changes for the upcoming 2012 edition (see “It’s Almost Here, ”May 2011 Electrical Contractor Magazine. It’s time for that feeling once again as we move toward completion of the 2015 edition.

What’s new?

Some of the terminology used during this revision cycle has changed. Request for Proposals are now called Public Input (PI), and this revision cycle had 448 PIs. The Report on Proposals (ROP) is now called the First Draft, and what was previously called the Report on Comments (ROC) is referred to as the Second Draft.

The changes this article outlines are based on what was known at the time of writing. It does not include every change made, and much of the language is paraphrased due to space limitations. Since the NFPA Standards Council has not formally approved the final document, there is always the possibility of additional changes. Therefore, always refer to the final approved version when it is published.

Global changes

Several terms used throughout NFPA 70E have been changed for the 2015 edition. The left column in the terms table above refers to the term used in the 2012 edition and the right column lists the new corresponding term for 2015.

Please note: all references to hazard/risk category (HRC) have been deleted throughout the standard. Arc flash PPE category is the revised term.


Short Circuit Data – Per Unit, Amps and Symmetrical Components

Making Sense of the Numbers
Utility Company Short-circuit Data For Arc Flash Studies

Electrical Contractor Magazine – November 2012
Jim Phillips, P.E.

One of the first steps in performing an arc flash hazard calculation study is to request the short-circuit data from the electric utility company. This information is critical because it defines the magnitude of current that could flow from the utility and is used as a starting point for arc flash calculations.

In addition to requesting this data for normal operating conditions, it should also be requested based on minimum short-circuit current conditions, if available. The minimum condition could be for a utility transformer or transmission line out of service or similar scenario. The minimum value can then be used to determine if the lower current could result in a protective device operating more slowly, which may increase the total incident energy during an arc flash.

Too many numbers—now what?
Unfortunately, a single standardized format for short-circuit data does not exist. Instead, depending on the individual utility, data may be provided in one of several different formats such as the following:

• Short-circuit amperes (A)
• Short-circuit megavolt-amperes (MVA)
• Per-unit and symmetrical components

Of course, with multiple formats, confusion could (and often does) result. I will compare the different formats using a three-phase short-circuit current of 6,000A at the 23-kilovolt (kV) level. Since arc flash calculations are based on a three-phase model, only the three-phase short-circuit calculations are used. Some of the values are slightly rounded.

Short-circuit ampere format
This is the simplest format because it defines the short-circuit current in terms of amperes at a specified location. As an example, the utility has provided the following information:

Short-circuit amperes three-phase = 6,000A
Voltage = 23 kV line-to-line

Since the data is already in terms of amperes, no additional calculations are necessary.

Short-circuit MVA format
Utility companies often provide short- circuit data in terms of short-circuit MVA. This format combines the short-circuit current with the voltage and the square root of 3 (for a three-phase representation) to provide the data in terms of short-circuit power. Below is an example of the MVA format.

Three-phase short-circuit MVA = 240 MVA
Voltage = 23 kV line-to-line

To convert three-phase short-circuit MVA to short-circuit current in amperes, use the following equations:

Short-circuit amperes = [MVA x 1,000] / [kV line-to-line x the square root of 3]

where 1,000 is the conversion from MVA to kVA

Short-circuit amperes = [240 MVA x 1,000] / [23 kV line-to-line x 1.732]
Short-circuit amperes = 6,000A