Arc Flash & Electrical Power Training | Brainfiller

Arc Flash Study Top 10 FAQs Part #2

How Does Everyone Else Do This? By Jim Phillips 3-Part Series   ELECTRICAL SAFETY PRACTICES
  1. Does your company or client permit energized work where the incident energy is greater than 40 calories per centimeter squared (cal/cm2)?

This question is about the 40 cal/cm2 limit found in Informational Note 3 of NFPA 70E 130.7:“When incident energy exceeds 40 cal/cm2 at the working distance, greater emphasis may be necessary with respect to de-energizing before working within the limited approach boundary of the exposed electrical conductors or circuit parts.” (This language is from the 2012 edition of NFPA 70E, which was in use when this question was asked.)

Although it is only an informational note, many Code users take this value as an absolute go/no-go when it comes to energized work and prohibit work at locations where the incident energy exceeds 40 cal/cm2. The concern is frequently about blast pressure and the legal aspects of a standard containing a reference to 40 cal/cm2 in this context even though it is an informational note. Many times, when there is a large prospective incident energy, it is because of a long arcing time (e.g., a protective device may take a long time to operate).

Question: Does your company or client permit energized work where the incident energy exceeds 40 cal/cm2?

Yes: 9%

No: 59%

It depends: 21%

We don’t perform energized work: 11%

Of the many comments that were also provided in response to this question, it was pointed out that testing for dead means assuming the conductor is live. So, technically, live work is being performed above 40 cal/cm2.


  1. What do you do if an unqualified person enters the limited-approach boundary?

Unqualified people are not permitted within the limited-approach boundary, unless they are advised of the hazards and continuously escorted. Sometimes people, such as managers, owners and others, will show up for various reasons, assuming that only the person performing the work needs to be qualified (and protected). This, of course, is incorrect.

Question: If an unqualified person enters the limited-approach boundary while energized work is being performed, the response should be:

Keep working: 0%

Stop working: 27%

Insist they leave the area: 66%

Report them: 2%

Something else: 5%

(Respondents were instructed to select all that applied.)


  1. How is your company or client’s condition of maintenance of electrical equipment?

This question was asked as a result of the 2015 edition of NFPA 70E placing more emphasis on the condition of the electrical equipment, such as in 110.1(B), which states: “The electrical safety program shall include elements that consider condition of maintenance of electrical equipment and systems.”

Question: What is the condition of maintenance of your/your client’s electrical equipment?

Excellent—Better than most: 2%

Average—Pretty typical: 53%

Poor—What is maintenance?: 30%

We have many clients/locations; we set it all: 15%

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