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Standard for Electrical Safety In The Workplace (2015 Edition)

Standard for Electrical Safety In The Workplace

NFPA 70e- What Does It All Mean?

We understand the standards, regulations, and details of the NFPA 70e can be VERY confusing. It is our goal, to make the information accessible and easy to understand, for all who wish to learn more.

 

The previous versions of the NFPA 70e®, NEC Electrical Code® (NEC®), were confronted with various problems. The largest, was the conflict between the OSHA standard and other national and local standards. The updated version is a result of a new standard, tailored to fulfill OSHA’s responsibilities, while still being compliant with the NEC.

 

Arc Flash Hazard:

  • An arc flash hazard is a dangerous condition associated with the possible release of energy caused by an electric arc. This occurs when a grounded object comes in contact with an energized object.  This low impedance path creates a short circuit and an electrical arc. 
  • An arc flash is measured in calories per centimeter squared (cal/cm²). For example, one calorie would be the equivalent of holding your finger over the tip of a lit match for one second.
  • An Arc flash produces some of the highest temperatures known on earth, up to 35,000°F, that is almost 4x hotter than the surface of the sun (9,000°F).
  • This heat can vaporize nearly all materials on the face of the earth.

Protective Device Coordination Study:

  • The coordination study is a very important part of the overall arc flash study.
  • Nearly all breaker manufacturers ship their breakers with factory minimums.
  • Many breakers in the power system have (multiple) different settings that can be field adjusted to control how fast the breaker trips, in the event of a short circuit condition.
  • The breakers in the system are adjusted in order to minimize the arc flash energies to their lowest possible values, while still providing the highest level of electrical system reliability and eliminating nuisance tripping.
  • If a coordination study was not performed when the breakers were first installed, it is no longer a question of IF problems will occur, but WHEN will they occur. Just one 20amp circuit can take down an improperly set 4000amp main breaker, and shut down the whole building.

Short Circuit Study:

  • The short circuit study is a required part of any arc flash study. The reason for this portion of the study is to determine the amount of available short circuit current in the power system.
  • This available fault current at each point in the power system is then compared to the specific breaker or protective device’s operating/trip time.
  • The device’s operating/trip time determines the amount of arc flash energy that could be released at each point in the power system.
  • The short circuit study also verifies that each piece of equipment has an adequate interrupting rating for its’ position in the power system.

 

The information presented within this page is in no way endorsed by the NFPA, OSHA, NEC, or any governing body. It is merely an interpretive overview of the information found within the various publications pertaining to the NFPA 70e standard. Pro-Line Inspections, LLC cannot be held responsible, nor does it recommend using this information, without first referencing the standards implemented by OSHA® and the NFPA®. For more information, please click here.