Know what you’re getting into to protect against arc flash hazard
Jeffrey Sargent is NFPA’s senior electrical specilist and is staff liason for NFPA 70E.
NFPA Journal, July/August 2010
Recently, provisions were added to NFPA 70®, National Electrical Code® (NEC®), and NFPA 70E® requiring that labels on electrical equipment convey an important safety message to employees who have to examine, adjust, service, or maintain energized electrical equipment. Reading those labels is akin to a consumer reading a product label: They tell you what you are getting, or, in the case of energized electrical conductors and circuit parts, what you are getting into.
Why this is not the time to ignore your electrical power system
The labeling requirements in the two codes differ. The labels required by the NEC, first introduced in Section 110.16 in the 2002 edition, warn that an arc flash hazard exists and tell employees to proceed with caution if energized work is to be performed. Those in NFPA 70E take the next step in ensuring that employees can safely proceed with the task at hand once the decision to work on energized equipment has been made, validated, and documented.
For certain types of electrical equipment likely to require examination, adjustment, servicing, or maintenance while energized, the completed installation must bear a label that warns qualified persons that the potential for an arc flash hazard exists. The label must be visible so the qualified person can read it before undertaking any task that will expose him or her to the arc flash hazard, defined in NFPA 70E as “a dangerous condition associated with the possible release of energy caused by an electric arc.”
The labeling requirement in the NEC is triggered when an employee might possibly be exposed to an arc flash hazard, as defined in NFPA 70E. The accepted threshold in NFPA 70E for an arc flash hazard is an arc flash that exposes some part of the employee’s body to an incident energy level above the threshold for a second-degree burn, which is 1.2 calories/square centimeter. The NFPA 70 provision identifies types of equipment that are likely to require examination, adjustment, service, or maintenance while energized, including but not limited to switchboards, panel boards, motor control centers, and industrial control panels.
Employees approaching electrical equipment bearing a label warning of a potential arc flash hazard must determine whether the task can be performed while the equipment is energized, in accordance with Section 130.1(A) of NFPA 70E. The NEC-required label advises of an extremely serious hazard and, as part of being a qualified person, the employee must understand the potential consequences of working on the energized equipment and, if “energized work” is permitted under Section 130.1(A), what steps must be taken to mitigate arc flash hazard exposure. The NEC label can be viewed as a first line of defense meant to get the qualified person to think carefully about what he or she is about to do.
The NEC scope covers the installation of electrical equipment and conductors, and provides requirements that cover employee safety in anticipation that some equipment will be worked on while energized. This is the reason requirements, such as those in Section 110.16 on the arc flash hazard warning label and Section 110.26(A) on working space, exist in the NEC. Although the NEC anticipates that the equipment covered in Section 110.16 may be worked on while energized, it may not be, which is why the NEC labeling requirement does not mandate more specific provisions on the requisite level of personal protective equipment (PPE). Fine Print Note No. 1 for Section 110.16 points to NFPA 70E for the detailed information on strategies and methods to protect employees. Task-oriented PPE requirements fall within the scope of NFPA 70E.
Section 130.3(C) covering the equipment labeling requirement was added to the 2009 edition of NFPA 70E, and that is where you can find detailed information about what equipment labels require to protect employees against the arc flash hazard.