PROTECTING YOUR EMPLOYEES FROM ARC FLASH BY MEL NACIONAL

OVERVIEW

An arc flash event can be outright dangerous and deadly.? Per a 2022 article in Electrical Contractor magazine, arc flash incidents in the United States result in around 400 fatalities per year, 7,000 burn injuries and 2,000 hospitalizations.? This is based on 5-10 arc flash incidents occurring every day.? In order to reduce the risk of exposure to arc flash hazards, an arc flash study/analysis & arc flash labels installation should be performed for each facility.? The arc flash study shall be updated when changes occur that could affect the results of the analysis and review for accuracy of this analysis shall not exceed 5 years as discussed in NFPA70E article 103.5.G.

Protecting employees from the risk of exposure to arc flash hazards when working on energized electrical equipment is the responsibility of the employer and employee.? The employer should provide the necessary tools and training for the employee to safely operate and/or perform installation, testing, or maintenance of the electrical equipment.?

WHAT IS ARC FLASH?

An arc flash is the light and heat produced from an electric arc supplied with sufficient electrical energy to cause substantial damage, harm, fire, or injury.? There are many variables involved in determining an arc flash incident energy, but we’ll cover the main three components: short-circuit current, protective device trip time, and working distance.? These three components simplify the essence of what is involved in determining an arc flash value, which is an incident energy in calorie per centimeter squared unit.

The arc flash incident energy calculated for a given panelboard in a distribution system is dependent on the short circuit current flowing through it, the trip time of the upstream protective device feeding it, and the worker’s distance to arc source. ?The short circuit current is the hardest of the three components to adjust because it will require changing the electrical distribution design.? On the other hand, the overcurrent protective device trip time and working distance can be adjusted easily without changing the distribution system; thereby lowering the incident energy exposure.?

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WHAT IS SHORT-CIRCUIT CURRENT?

Short-circuit current is the maximum amount of current that flows through a power system in the event of a short circuit.? This includes fault contributions from the utility company and all rotating machines (motors and generators) connected within an electrical distribution system.? This value is typically compared to the maximum interrupting rating of a breaker or fuse inside a panelboard.? This maximum interrupting rating is also known as “Ampere Interrupting Capacity” (AIC).? The AIC rating is the maximum short circuit current that a protective device can safely operate without causing equipment damage or injury to people.? In the event of a fault inside a panelboard, the breakers/fuses is subjected to the thermal and magnetic stresses within the first half-cycle of a short circuit.? During this period, it is critical that the breaker/fuse’s AIC rating is higher than the short circuit current flowing through it to maintain system integrity.? A high magnitude short-circuit current that is higher than the overcurrent protective device’s AIC rating may cause catastrophic event resulting in severe arc flash.

WHAT IS PROTECTIVE DEVICE TRIP TIME?

Protective device trip time is the amount of time a breaker/fuse operates to interrupt a fault in the electrical distribution system.? These overcurrent protective devices have an inverse time and current relationship.? The higher the current the lower the time and vice versa.? In the case of a breaker protecting a panelboard downstream that is subjected to a fault, the time it takes for the breaker to operate depends on the amount of short circuit current flowing through it, and its clearing time (based on the breaker’s trip unit time-current characteristics curve) to physically disconnect the circuit.? It is important that protective devices are tested and maintained as recommended by the manufacturer to ensure proper operation.? A protective device that is poorly maintained may not operate effectively and may fail to clear the fault in the system resulting in a severe arc flash event.

WHAT IS WORKING DISTANCE?

Working distance is defined by IEEE 1584 as the distance between the worker’s face and chest to a potential arc source.? This working distance is typically 18 inches.? The relationship between the distance and the incident energy is inverse squared.? For example, a distance of twice the typical length, will have reduced the incident energy by a factor of 4.? On the other hand, the closer the distance to the point of the arc source will increase the incident energy rapidly.?

HOW CAN YOU PROTECT YOUR EMPLOYEES FROM THE DANGER OF ARC FLASH?

There is no absolute approach in completely protecting anyone from the danger of arc flash when working on an energized equipment, but there are tools available to use that could reduce the risk of exposure to arc flash hazards.? The arc flash study & arc flash labels, personal protective equipment (PPE), and arc flash hazard safety training are important tools to use for this task.? The study is used to determine the arc flash and shock hazards associated with each piece of electrical equipment analyzed.? Values determined include but are not limited to arc flash boundary (ft in), incident energy (cal/cm2), working distance (in), nominal voltage when covers removed, limited approach boundary (ft in), restricted approach boundary (ft in), insulating gloves rating, equipment designation, date of study completed, etc.? These values are needed by the worker in order to select the appropriate personal protective equipment (PPE) to wear to protect themselves when working on this piece of equipment.? The PPE is considered the last defense against exposure to an arc flash.? The PPE a worker must use includes but are not limited to the arc flash suit, hardhat, eye protection, hearing protection, gloves (rubber & leather), EH shoes, etc.? Last critical tool is an arc flash hazard safety training.? This safety training encompasses the fundamental understanding of electrical arc flash and shock hazards associated with working on energized electrical equipment.? It explains the values determined in the arc flash study and printed in the arc flash label and how they apply prior to commencing work.? And it also discusses how to select the appropriate PPE to use as well as maintain and care for the PPE.? Employee protection against arc flash hazards in the workplace is the utmost importance.? By utilizing tools available, employees’ risk exposure to arc flash hazards can be minimized.

HOW DO YOU PERFORM AN ARC FLASH ANALYSIS?

Performing an arc flash analysis is typically conducted or supervised by a professional engineer in charge of the project, who is specialized in this field of analysis.? This analysis is very extensive and requires years of experience in conducting short circuit study, protective device coordination study, and arc flash study.? Each study is specialized in nature, where determination of equipment’s withstand rating is considered to ensure that it can handle the maximum short circuit current that flows through it; coordination of protective devices in the distribution system is optimized in order to allow the protective device closest to the fault to operate first; and lastly, the maximum incident energy value at each equipment is determined in order to select the appropriate personal protective equipment (PPE) a worker will use.? The software analysis tools used to conduct these studies are widely available and have been in use in the industry for a long time.? ETAP by OTI, SKM PowerTools, ESA’s Easy Power, etc. to name a few are very good tools for conducting these studies.? ??Modeling the facility’s electrical distribution system’s single-line diagram in the software analysis is the initial step.? This will depict the utility & generation delivery point, power cables and conductors connecting the equipment to the main switchboard and all subsequent electrical equipment, as well as connections to all overcurrent protective devices associated with each load.? In order to complete the model, data for each electrical component in the distribution system must be entered into the software model.? These are field gathered data, which includes equipment nameplate, catalog numbers, model/style, size, lengths, settings, etc.? During field data gathering, assessment of the condition of the equipment and potential code violation is performed.? The final arc flash study report contains the objectives, methods, assumptions, findings, recommendations and site survey results.? Any findings resulting in failure to withstand a short circuit, lack of coordination, and high incident energy above the maximum 40 cal/cm2 limit is noted and a recommendation is provided to improve the system.? The final arc flash study report is stamped and signed by a professional electrical engineer registered in the state where the project is physically located having responsible charge for the report.

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WHAT ARE THE BENEFITS OF AN ACR FLASH ANALYSIS?

Any facility can benefit from an arc flash study where a worker operates and/or performs installation, testing or maintenance on energized electrical equipment.? Facilities such as water and/or wastewater operations, hospitals, office buildings, etc. can significantly benefit having a completed arc flash study because it can help identify and fix potential arc flash hazards before an accident occurs. ?The cost of the study is much lower than the potential cost of an arc flash incident.? Direct and indirect cost such as loss of worker due to injury or death, medical expenses, lost operation, equipment damage and potential legal liabilities for an arc flash incident can put a huge financial burden on a company or entity.? The importance of an arc flash study is to help protect the employee from a potential arc flash hazards within the electrical distribution system that can lead to injury or death.