{"id":48296,"date":"2026-02-17T17:10:10","date_gmt":"2026-02-18T00:10:10","guid":{"rendered":"https:\/\/brainfiller.com\/?p=48296"},"modified":"2026-03-03T11:42:52","modified_gmt":"2026-03-03T18:42:52","slug":"arcing-fault-current-nfpa70e","status":"publish","type":"post","link":"https:\/\/brainfiller.com\/es\/nfpa-70e\/arcing-fault-current-nfpa70e\/","title":{"rendered":"Arcing Fault Current, NFPA 70E and IEEE 1584"},"content":{"rendered":"
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Pregunta:<\/strong> Why isn\u2019t there a fixed percentage difference between the bolted and arcing fault current?<\/p>

IEEE 1584, Guide for Performing Arc-Flash Hazard Calculations<\/em>, provides the technical foundation used to calculate incident energy and arc-flash boundaries in electrical power systems. A key element in this standard is the calculation of the arcing fault current<\/strong>, which differs from the bolted fault current<\/strong> typically obtained from short-circuit studies. While IEEE 1584 defines the calculation methodology, NFPA 70E relies on these results<\/strong> as part of an arc flash risk assessment used to establish practical electrical safety requirements for workers.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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Bolted Fault Current <\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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A bolted fault represents a theoretical condition with zero impedance between conductors, resulting in the maximum available fault current. The term reflects laboratory conditions during a short circuit test. When calibrating the circuit, the test circuit is shorted by \u201cbolting\u201d the phases together with large bus bars as I have done in the laboratory and illustrated in the photo.\u00a0 Hence the term \u201cbolted fault current\u201d<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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Jim uses a busbar to \"bolt\" the phases together in the lab<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Corriente de falla de arco<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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An arcing fault, however, includes the impedance of the electrical arc itself, which limits current flow. For this reason, arcing fault current is always lower than bolted fault current.<\/p>

The first theoretically derived equations from the 1980\u2019s did not account for the arcing current and only used the bolted fault current.\u00a0 Subsequent work in the late 1990\u2019s recognized the importance of the arcing current and its potential effect on how a protective device may operate.\u00a0 This later work referenced technical research that indicated the arcing current at 480v could be as low as 38 percent of the bolted current and therefore 38 percent was a \u201cfixed\u201d value that was suggested.<\/p>

Research that was part of the development of the 2002 Edition of IEEE 1584 determined the percentage difference between bolted and arcing fault current varies significantly with system voltage and also the magnitude of bolted fault current<\/strong>, which directly affects arc-flash hazard analysis results used to comply with NFPA 70E 130.5 Arc Flash Risk Assessment.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Voltage and Arcing Current<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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At lower system voltages<\/strong>, particularly in the 208 V to 600 V range, the arc impedance is relatively high compared to the system impedance. This results in a larger percentage reduction<\/strong> between bolted and arcing fault current. In many low-voltage systems, the arcing current may be substantially lower than bolted fault current. This can cause protective devices to operate in their time-delay region resulting in a significant increase in the arc duration and incident energy.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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System Impedance and Arcing Current<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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The bolted fault current follows a similar trend. Higher bolted fault currents correspond to a lower system impedance. As with the voltage trend, this means that the arc impedance represents a larger portion of the total circuit impedance in systems with higher available fault current. Conversely, as the bolted fault current decreases, the percentage difference between the bolted fault current and the arcing fault current also decreases.<\/p>

In each case, the percentage difference between the bolted and arcing current is not a linear relationship and must be calculated using very robust equations from IEEE 1584.<\/p>

Arc flash studies used to comply with NFPA 70E requirements, recognize this relationship and an arc-flash risk assessment <\/strong>based on incident energy calculations<\/a> needs to account for realistic arcing conditions rather than relying solely on maximum short-circuit current.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Medium Voltage and Beyond<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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As system voltage increases such as medium voltage systems, the electrical arc becomes more stable and the arc impedance relative to the system impedance has less impact. Consequently, the difference between bolted and arcing fault current decreases<\/strong>, and arcing current more closely approaches bolted fault current. This behavior is reflected in IEEE 1584 calculation models and directly influences incident energy values used to determine PPE arc ratings, arc-flash boundaries<\/a>, and safe work practices<\/strong> under NFPA 70E.<\/p>

For systems above 15 kV<\/strong><\/a>, the difference between bolted and arcing fault current is minimal. Alternative arc flash models above 15 kV treat these values as effectively the same for higher voltages.\u00a0<\/p>

In practice, NFPA 70E establishes the \u201cwhat\u201d of electrical safety\u2014risk assessment, labeling, PPE, and work practices\u2014while IEEE 1584 defines the \u201chow\u201d of arc-flash calculations<\/strong>. Understanding how arcing fault current varies with voltage and other factors is one of the many critical steps in performing arc flash studies that support compliance with NFPA 70E and improve worker safety.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Acerca de Jim Phillips<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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With a career beginning in 1981 and Brainfiller launching in 1987, Jim has built a global reputation as a trusted leader in electrical safety.<\/p>

He currently:<\/p>