You would be exposed to a certain amount of heat energy. So let’s say you are standing in front of 30 amp disconnect (600 volts) and an arc flash occurs. Typically, it’s measured in calories per square centimeter (cal/cm2). Incident energy is the amount of heat energy produced by the arc flash explosion. In order to understand the arc rating, you first need to understand what it is correlated to… There are many ways to achieve arc flash protection, but quite often your only option will be to use electrical arc flash PPE.Įnsuring you are covered head to toe with equipment that is properly rated is paramount to your safety. Using PPE to Protect Yourself from an Arc Flash. Primarily, arc flash PPE is divided into the following subgroups:Īll arc flash apparel and equipment must be given a specific arc rating to ensure that it meets or exceeds the hazard levels present where the work is to be performed. This takes into account various system variable beyond knowing the system voltage in order to accurately determine the proper distance for the Arc Flash Boundary.Arc flash personal protective equipment (PPE) is a combination of clothing and safety equipment worn for protection from arc flash and shock hazards by a person performing electrical work. The Arc Flash Boundary is only determined through a detailed power system analysis referred to as an Arc Flash Analysis. Know your voltage and have access to the table is all that is needed to determine the shock boundaries.ĭetermining the Arc Flash Boundary is not nearly as easy as determining the three shock boundaries. The boundaries are directly related to their voltage levels and do not change based upon various system attributes. The boundaries that focus on protecting workers from electrical shock and electrocution Limited Approach, and Restricted Approach, are determined by referencing the NFPA 70E Tables 130.4(C)(a) for AC systems and 130.4(C)(b) for DC systems. An approved work permit where applicable is needed to cross this boundary, with some form of documentation in place at a minimum. Qualified workers must don applicable arc flash PPE as well as shock PPE appropriate for the voltage a worker is exposed to. Non-qualified workers are prohibited from crossing the restricted approach boundary and entering the restricted space. The Restricted Approach Boundary may only be crossed by a qualified worker. However, when the arc flash boundary is larger, be sure proper arc flash PPE is worn within the limited approach boundary. In many cases the limited approach boundary is the farthest electrical boundary that exists. To cross the limited approach boundary a worker must be qualified or otherwise escorted by a qualified person. No matter who crosses the Arc Flash Boundary, proper PPE is required that meets the requirements of the NFPA 70E.ĭistance from an exposed live part within which a shock hazard exists. Detailed formulas for determining the arc flash boundary can be found in the NFPA 70E and IEEE 1584.īoth Qualified and Non-qualified can cross the Arc Flash Boundary as long as long as Qualified personnel supervision is present. This boundary is calculated based upon specific system information, and can apply when exposed energized conductors or circuit parts are present, or with doors and equipment closed if interacting in a manner that could cause an arc. It is defined as the distance at which a worker is exposed to 1.2 calories/cm2 of incident energy, which represents the onset of a second degree burn. The Arc Flash Boundary deals specifically with arc flash hazards and determines when arc flash PPE shall be required. These boundaries are not calculated and apply only when exposed energized conductors or circuit parts are present. The Limited, and Restricted approach boundaries deal strictly with shock prevention and are based upon nominal system voltage. The arc flash boundary has a primary purpose of preventing burn injury due to arc flash incidents. The third boundary is the arc flash boundary. Two boundaries deal specifically with shock hazards and are intended to prevent shock and electrocution. The NFPA 70E defines three boundaries for electrical workers to observe.
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