The definitions are imperative to know as we use these terms explaining the Arc Flash Risk Assessment and the NFPA 70E. These definitions have been gathered from the 2018 Edition NFPA 70E Handbook.
Arc Flash Hazard
A dangerous condition associated with the possible release of energy caused by an electric arc. Informational Note No. 1: An arc flash hazard may exist when energized electrical conductors or circuit parts are exposed or when they are within equipment in a guarded or enclosed condition, provided a person is interacting with the equipment in such a manner that could cause an electric arc. Under normal operating conditions, enclosed energized equipment that has been properly installed and maintained is not likely to pose an arc flash hazard.
Informational Note No. 2: See Table 130.7(C)(15)(a) and Table 130.7(C)(15)(A)(a) for examples of activities that could pose an arc flash hazard.
An arc flash hazard exists if a person is or might be exposed to a significant thermal hazard. If the thermal hazard is of a severity that might expose a person to 1.2 calories per square centimeter
(cal/cm2) or more of incident (thermal) energy, the hazard is considered to be significant. Personal protective equipment with a rating that exceeds the thermal hazard must be worn. Use of personal protective equipment for exposures with less than 1.2 cal/cm2 incident energy is certainly permitted and might be deemed appropriate by the employer and employee.
In certain conditions, an arcing fault contained within equipment could generate a pressure wave and destroy the integrity of the enclosure. The technical committee suggests that the term interacting with the equipment could mean opening or closing a disconnecting means, pushing a reset button, or latching the enclosure door. However, if equipment is installed in accordance with the requirements of the NEC, maintained adequately, and operated normally, the chance of one of these actions initiating an arcing fault is remote.
Arc Flash Risk Assessment
A study investigating a worker’s potential exposure to arc flash energy, conducted for the purpose of injury prevention and the determination of safe work practices, arc flash boundary, and the appropriate levels of personal protective equipment (PPE).
An arc flash hazard analysis determines the flash protection boundary and the amount of incident energy that could be impressed on an employee as a work task is being performed and is in addition to the shock hazard analysis. The analysis can take one of several different forms.
An arc flash hazard analysis is necessary regardless of any label or marking on the surface of electrical equipment. Referring to a warning label could be one step in the analysis; however, the analysis also must consider risk. When the analysis is complete, the employee has sufficient information for selecting the necessary arc flash personal protective equipment (PPE) and the work practices necessary to minimize any exposure to a thermal hazard. Part of the analysis includes determining the arc flash boundary and the incident energy.
Arc Flash Suit
A complete arc rated clothing and equipment system that covers the entire body, except for the hands and feet.
The value attributed to materials that describe their performance to exposure to an electrical arc discharge. The arc rating is expressed in cal/cm2 and is derived from the determined value of the arc thermal performance value (ATPV) or energy of break open threshold (EBT) (Should a material system exhibit a break open response below the ATPV value). Arc rating is reported as either ATPV or EBT, whichever is the lower value.
Balaclava (Sock Hood)
An arc rated hood that protects the neck and head except for the facial area of the eyes and nose.
Boundary, Arc Flash
When an arc flash hazard exists, an approach limit at a distance from a prospective arc source within which a person could receive a second degree burn if an electrical arc flash were to occur.
Boundary, Limited Approach
An approach limit at a distance from an exposed energized electrical conductor or circuit part within which a shock hazard exists. The limited approach boundary is not related to arc flash or incident energy. The limited approach boundary is a shock protection boundary intended to define the approach limit for unqualified employees and to eliminate the risk of contact with an exposed energized electrical conductor. The term is used to identify a minimum distance that is considered to be safe. When an employee is closer than this minimum distance, special considerations are necessary for protection. Any person working within the limited approach boundary of exposed energized circuit conductors or circuit parts can do so only if an energized work permit has been completed and authorized except as specified in 130.3(B)(3). If an unqualified employee is required to work within the limited approach boundary, the employee must be directly and continuously supervised by a qualified person.
Boundary, Restricted Approach
An approach limit at a distance from an exposed energized electrical conductor or circuit part within which there is an increased likelihood of electric shock, due to electrical arc-over combined with inadvertent movement, for personnel working in close proximity to the energized electrical conductor or circuit part.
The restricted approach boundary is a shock protection boundary that is not related to arc flash or incident energy. It is the approach limit for qualified employees. Qualified employees should have the knowledge and ability to avoid unexpected contact with an exposed energized conductor. If it is necessary for a qualified employee to cross the restricted approach boundary, the employee must be protected from unexpected contact with the conductors that are energized and exposed. An energized electrical work permit is required to be completed and authorized before employees work within the limited, restricted, and prohibited approach boundaries, except as permitted by 130.3(B)(3).
A device designed to open and close a circuit by non-automatic means and to open the circuit automatically on a predetermined over-current without damage to itself when properly applied within its rating. [70, 100]
Free from any electrical connection to a source of potential difference and from electrical charge; not having a potential different from that of the earth.
A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply. [70, 100]
Disconnecting means can be one or more switches, circuit breakers, or other rated devices that might be used to disconnect electrical conductors from their source of energy. Only disconnecting means that are load rated should be used to disconnect an operating load.
Disconnecting (or Isolating) Switch (Disconnector, Isolator)
A mechanical switching device used for isolating a circuit or equipment from a source of power. These devices are intended to be operated after interrupting and removing the load current. Locks and tags can be installed on these devices.
A dangerous condition such that contact or equipment failure can result in electric shock, arc flash burn, thermal burn, or blast.
Fire, shock, and electrocution have been considered to be electrical hazards for many years. Since the 1995 edition of NFPA 70E, arc flash has been recognized as an electrical hazard. The arc flash hazard currently is defined to consider only the thermal aspects of an arcing fault. Other hazards include flying parts and pieces and the pressure wave (blast) that is generated in an arcing fault. Other electrical hazards also might be associated with an arcing fault.
Electrical equipment that is energized at less than 50 volts is not normally considered to be an arc flash hazard. However, employees should recognize that the effects of an arcing fault are related to available incident energy. In some instances, an arcing fault hazard might be significant. If exposure to electric burns or explosion hazards due to electric arc exists, an electrically safe work condition and PPE could be needed in accordance with the requirements of Article 130.
Recognizing hazards associated with the use of electrical energy and taking precautions so that hazards do not cause injury or death.
Electrical safety is a condition that can be achieved by doing the following:
· Identifying all of the electrical hazards
· Generating a comprehensive plan to mitigate exposure to the hazards
· Providing protective schemes including training for both qualified and unqualified persons
Electrically Safe Work Condition
A state in which an electrical conductor or circuit part has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.
Establishing an electrically safe work condition is the only work practice that ensures that an electrical injury cannot occur. However, workers should recognize that operating disconnecting means and verifying absence of voltage might in themselves be hazardous work tasks.
Until the electrically safe work condition exists, a risk of injury from electrical energy exists.
Exposed (as applied to energized electrical conductors or circuit parts). Capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to electrical conductors or circuit parts that are not suitably guarded, isolated, or insulated.
An over current protective device with a circuit-opening fusible part that is heated and severed by the passage of over-current through it.
An unintentional, electrically conducting connection between an
ungrounded conductor of an electrical circuit and the normally non–current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.
Covered, shielded, fenced, enclosed, or otherwise protected by means of suitable covers, casings, barriers, rails, screens, mats, or platforms to remove the likelihood of approach or contact by persons or objects to a point of danger. [70, 100] When an exposed conductor is guarded, a person who is approaching the exposed conductor is unlikely to contact the conductor. A person must be exposed to a potential difference of 50 volts or more for a shock hazard to exist.
A person might be exposed to hazards associated with an arcing fault even when the conductor is guarded. A guarded conductor protects a person from exposure to shock or electrocution but not to arc flash hazards.
The amount of thermal energy impressed on a surface, a certain distance from the source, generated during an electrical arc event. Incident energy is typically express in calories per square centimeter (cal/cm2).
Incident energy could be expressed in several different terms, such as calories per square centimeter, joules per square centimeter, or calories per square inch. However, incident energy must be expressed in the same terms in which the PPE is thermally rated. ASTM standards require PPE to be rated in calories per square centimeter, which enables an employee to select adequate PPE. Physical characteristics of materials vary, causing materials to react differently when exposed to elevated temperatures. Some man-made materials melt before igniting when exposed to the thermal energy generated in an arcing fault. Some other materials ignite and burn when exposed to an arcing fault. The most severe injuries occur when clothing melts onto an employee’s skin or when an employee’s clothing ignites and burns. Many materials melt or ignite when heated to a few hundred degrees Fahrenheit. Incident energy raises the temperature of an employee’s clothing or skin when exposure to an arcing fault exists. Predicting the amount of available incident energy is critical to prevent injury from melting or burning clothing or from direct skin exposure to incident energy.
Incident Energy Analysis
A component of an arc flash hazard analysis used to predict the incident energy of an arc flash risk assessment for a specified set of conditions.
An incident energy analysis is an important part of performing the arc flash hazard analysis for a specific task and item of electrical equipment. A calculated or computed incident energy analysis provides an installation-specific analysis of the incident energy that an employee will be exposed if an arc flash incident does occur. This focused information allows the selection of PPE based on the conditions associated with the task being performed on a specific piece of electrical equipment.
Motor Control Center
An assembly of one or more enclosed sections having a common power bus and principally containing motor control units. [70, 100]. A motor control center typically contains starters, disconnect switches, power panels, solid-state drives, and similar components.
A single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic over-current devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front. [70, 100]
One who has demonstrated skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training to identify and avoid the hazards involved.
For a person to be considered qualified, he or she must understand electrical hazards associated with the work task being contemplated. Before selecting the necessary protective equipment
(PPE), he or she also must understand the proper application and the limitations of PPE and tools such as voltage testers. A qualified person must have the ability to recognize all electrical hazards that might be associated with the work task being considered. An employee could be qualified to perform one work task and not qualified to perform a different task. A qualified employee must understand the construction and operation of the equipment or circuit associated with the contemplated work task.
The latest revision of the OSHA definition for qualified person (1910.399 8/07) includes the phrase “has demonstrated skills.” To meet this requirement, the person has to actually demonstrate that he/she can perform the task. A dress rehearsal using appropriate PPE for the task will ensure that the employee can perform the task with the lighting limitations of the flash suit hood and the dexterity limitations of voltage-rated gloves with leather protectors.
A qualified person must understand how to select appropriate test equipment and apply that equipment to the work task. He or she must be trained to understand and apply the details of the electrical safety program and procedures provided the employer.
A qualified person must be able to perform a hazard/risk analysis and to react appropriately to all hazards associated with the work task. Although licensing programs administered by state and local governments typically have training requirements a candidate must meet prior to being examined and again periodically after procuring the license, the license in and of itself does not make a person qualified for all tasks that he or she may encounter.
Electrical work requires continuing education and demonstration of the necessary skills in order to maintain the requisite skill level to work safely. Part of being a qualified person is recognizing that energized electrical work is permitted only under the conditions specified in 130.2(A).
A dangerous condition associated with the possible release of energy caused by contact or approach to energized electrical conductors or circuit parts.
Tolerance of electrical current through the body varies from one person to another and also varies based on the path of the current through the body. Although it is not technically substantiated, tolerance seems to be related to current density. However, existing documentation indicates that any person might receive a shock if the amount of current exceeds 0.020 amperes. Any exposure to contact with a source of electrical energy that might result in this level of current is a shock hazard. In general, when the voltage is 50 volts or greater, a shock hazard exists.
Short-Circuit Current Rating
The prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria. [70, 100]
Short-circuit current ratings are marked on equipment such as panel-boards, switchboards, busways, contactors, and starters. Listed products are subjected to rigorous testing as part of their evaluation, which includes tests under fault conditions. Therefore, listed products used within their ratings are considered to have met the requirements of 110.10 in the NEC. The basic purpose of over-current protection is to open the circuit before conductors or conductor insulation is damaged when an over-current condition occurs. An over-current condition can be the result of an overload, a ground fault, or a short. Over-current protective devices (such as fuses and circuit breakers) should be selected to ensure that the short-circuit current rating of the system components is not exceeded should a short circuit or high-level ground fault occur. Wire, bus structures, switching, protection and disconnect devices, and distribution equipment all have limited short-circuit ratings and would be damaged or destroyed if those short-circuit ratings were exceeded. Merely providing over-current protective devices with sufficient interrupting ratings would not ensure adequate short-circuit protection for the system components. When the available short-circuit current exceeds the short-circuit current rating of an electrical component, the over-current protective device must limit the let-through energy to within the rating of that electrical component. Utility companies usually determine and provide information on available short-circuit current levels at the service equipment. Literature on how to calculate short-circuit currents at each point in any distribution generally can be obtained by contacting the manufacturers of over-current protective devices or by referring to IEEE 141-1993 (R1999), IEEE Recommended Practice for Electric Power Distribution for Industrial Plants (Red Book). Adequate short circuit protection can be provided by fuses, molded-case circuit breakers, and low- voltage power circuit breakers, depending on specific circuit and installation requirements.
A diagram that shows, by means of single lines and graphic symbols, the course of an electric circuit or system of circuits and the component devices or parts used in the circuit or system.
A switch intended for isolating an electric circuit from the source of power. It has no interrupting rating, and it is intended to be operated only after the circuit has been opened by some other means. [70, 100]
A large single panel, frame, or assembly of panels on which are mounted on the face, back, or both, switches, over-current and other protective devices, buses, and usually instruments. These assemblies are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets. [70, 100]
Equipment designed to withstand the effects of an internal arcing fault and that directs the internally released energy away from the employee.
Arc-resistant switch-gear provides protection from internal arcing fault when the equipment is closed and operating normally. If doors and covers (including fasteners) are not completely closed, workers are exposed to the hazards associated with an arcing fault just as if no arc-resistant rating existed. Such protection cannot be assured where the switch-gear is not specifically identified as being arc resistant.
A person who is not a qualified person.
Working On (energized electrical conductors or circuit parts).
Intentionally coming in contact with energized electrical conductors or circuit parts with the hands, feet, or other body parts, with tools, probes, or with test equipment, regardless of the personal protective equipment a person is wearing. There are two categories of “working on”: Diagnostic (testing) is taking readings or measurements of electrical equipment with approved test equipment that does not require making any physical change to the equipment; repair is any physical alteration of electrical equipment (such as making or tightening connections, removing or replacing components, etc.).
Any task requiring a person to cross the prohibited approach boundary and intentionally contact an energized electrical conductor or circuit part is considered to be working on the conductor or circuit part and is subject to all associated requirements including the selection of the appropriate level of PPE. Measuring voltage requires that the prohibited approach boundary be breached, suggesting that measuring voltage exposes a worker to an electrical hazard.
The definition of the term working on establishes two distinctly different types of tasks that are included within this definition: diagnostic testing and repair. By defining these two types of tasks considered to be working on, the definition suggests that different procedural approaches may be in order depending on the complexity task and an employee’s exposure to electrical hazards.