What is Arc Flash? Arc Flash is an electrical short circuit, where a high level of current passes through air. Arc Flashes cause electrical equipment to explode, resulting in an arc-plasma fireball with temperatures exceeding 35,000° F (the surface of the sun is 9000° F). These high temperatures cause rapid heating of surrounding air and extreme pressures, resulting in an arc blast. An arc blast is the explosive expansion of both the surrounding air and the metal in the arc’s path. In an arc blast, vaporized solid metal conductors expand several thousand times their original volume, and can travel at speeds in excess of 700mph. The result of this violent event is usually destruction of the equipment involved, fire, and severe injury or death to any nearby people. The explosion takes less than one second and produces a brilliant flash, intense heat, and a pressure blast potentially equivalent to several sticks of dynamite.

Do you need an Arc Flash Study for NEC Compliance?

You may ask why an Arc Flash study should be performed at your location. Well actually one is not required by the National Electrical Code (NEC), but we strongly suggest that you do have one done. The NEC only requires that Arc Flash labels be displayed to warn of potential electric Arc Flash hazards. If a study has not been performed at your installation, then you are missing out on a detailed study that includes the NEC required Arc Flash labels and suggestions to reduce Arc Flash energy. We go above and beyond the minimum NEC requirements and include labels that display very important detailed information, for example, Arc Flash Boundaries, level of PPE required with PPE description, Arc Flash Energy, and other device specific details.

Do you need an Arc Flash Study for NFPA70E Compliance?

The NFPA70E clearly states electrical equipment should not be worked on while in an energized state. However, the equipment is considered to be energized until verified it has been de-energized. During the verification process the employee is potentially exposed to energized electrical parts. This exposure of the employee to energized parts places a requirement on the employer to provide Personal Protection Equipment (PPE). The NFPA70E outlines what type of PPE is required to be provided by the employer. The employer has two options to determine the type of PPE that complies with the NFPA70E:

1.    NFPA70E, 2004,  article 130.3 states, “A flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash.”

1. This option requires the employer to provide either an independent outside source or a qualified internal source to perform this analysis in accordance with the calculations defined by the NFPA70E or IEEE 1584. This option defines what level of PPE is required.

2.    NFPA70E, 2004,  article 130.7(C-9) “Selection of Personal Protective Equipment” states, “When PPE is selected in lieu of flash hazard analysis, Table 130.7 (C-9a) shall be used to determine the hazard/risk category for a task.”

1. This option requires the employer and the employee to make the determination of what level of PPE is required. This option shall NOT be used if the system has a short-circuit capacity or fault clearing times greater than what the tables were designed for.

 

The NFPA70E requirements take into consideration that the electrical system should have been installed and maintained in accordance with the NEC. If the system has been improperly maintained or has underrated equipment installed, it is a VIOLATION of the NEC. Therefore, the guidelines provided by the NFPA70E may not adequately protect your employees. 

Personal Protective Equipment “PPE”

PPE is used to limit the injury incurred during a fault to a level no greater than the exposure of bare skin to an open flame for approximately 1 second (approx 1.2 cal/cm^2, a curable 2nd degree burn). If an Arc Flash study has not been performed at your installation, NFPA 70E has several tables that your “qualified personnel” should apply when determining PPE. In some cases the PPE worn by your “qualified personnel” is oversized for a certain task in a specific location. In other cases where improper equipment is installed or existing equipment is maintained improperly, the Arc Flash energy could be MUCH GREATER than what their PPE can protect them from. If a fault has an Arc Flash energy greater than 40 cal/cm^2 the pressure wave will be so great that PPE can no longer provide adequate protection. Our Arc Flash study provides suggestions on how to reduce Arc Flash energy to safer levels, and it also points out improperly maintained and installed equipment.

 

How to Reduce Arc Flash Energy

 

There are three ways that Arc Flash energy can be decreased. First, the available short circuit current from the utility could be decreased (probably not possible). Second, the impedance in the local power distribution system could be increased (may be difficult and/or expensive). Third, the trip time of protective devices could be

decreased. One of the more common suggestions that we have made to reduce Arc Flash energy is circuit breaker trip adjustment. The adjustment of circuit breaker tripping devices can decrease the amount of Arc Flash energy

that is the result of a fault. Care must be taken when implementing this solution, as protective device coordination may be affected when reducing the trip time of protective devices. A benefit of decreasing the Arc Flash energy

is that it could lower the level of PPE required.  

 

Why should we perform an Arc Flash Study for you?

 

• An Arc Flash study is not required by the NEC, but Arc Flash equipment warning labels are. If you do not    have any Arc Flash labels now, you need to install them.

  • These labels are included in our Arc Flash study.

   

• An Arc Flash study may be required by the NFPA70E.

  • If your system falls outside the boundaries set for the NFPA70E PPE tables, then an Arc Flash study is required.

  • We provide calculated Arc Flash energy values and labels that will be a key part of your Electrical      Safety training.

   

• If your electrical personnel do not know what level of PPE is required for a task, as per NFPA70E, you need    to inform them.

  • We inform you of what level of PPE is required by the NFPA70E by way of a detailed Arc Flash label     which can be placed on equipment.

   

• Do you have improperly maintained or installed equipment that would cause the increase of Arc Flash Energy  or increase the potential for a fault to occur?

  • During the process of gathering the details to make Arc Flash energy calculations your system will be analyzed for areas of concern.

    The following are common areas of concern:

    Circuit breaker trip settings   Using Motor Circuit Protectors “MCPs” as feeder breakers   Under-rated or improperly sized fuses and circuit breakers   Under-rated Motor Control Center “MCC” buss bracing    Under-rated MCC starters and feeder breakers   Under-rated Switchgear, Switchboards, and Panelboards

So, why not let us give you a quote to perform a detailed study that will include the required labels, required level of PPE details, and suggestions on how to decrease the available Arc Flash energy?

 

 

 

NIOSH (National Institute for Occupational Safety and Health) Regarding Arc Flash

 

With NIOSH approval, a link to NIOSH’s Arc Flash Training video has been added to our website. This video is approximately 26 minutes long, and could be a valuable tool to aid in informing personnel of the hazards of Arc Flash.

Contact: Don Elrod PE, Electrical Engineering Services Group Manager