Preventing an Arc-tastrophe
/Arc flash. It’s just two words and it can happen in a only few rapid moments. But it can cause extensive harm, painful consequences, and irreplaceable damage.
An arc flash is the result of an arcing fault between electrical conductor(s) and another electrical conductor(s) or ground with enough electrical energy. The fault gives off a rapid release of energy (light and heat). Air becomes the conductor. A massive amount of energy discharges during the arc flash or blast. This energy burns the conductors, vaporizing the copper and thus causing an explosive volumetric increase, the arc blast. This explosion propels deadly shrapnel and molten metal as it dissipates. This rapid release of energy can cause debilitating burns, other injuries and even death. But, It’s preventable. Spontaneous arc faults can stem from malfunctioning electrical equipment, improper precautions, negligent maintenance, or even unfitting electrical design.
Prevention: Hazard Analysis & Study
Employers and facility owners know that investing in the safety of their people, and their property is always worth it. A Hazard Analysis can identify areas in which preventative measures should be taken, where modifications should be made, and where risk factors become serious dangers. Among the hazard analysis and study include: Short Circuity Study, Protective Device Evaluation, and Protective Device Time Current Coordination Study.
Short Circuit Study:
The study calculates the maximum short circuit current the electrical power system may be subjected to at each equipment location through out the distribution network from the sources such as utilities, generators, and motors. The equipment includes substations, switchgear, motor control centers, and panels with their respective over current protective devices; generators; transforms; motors; and UPS equipment. The short circuit results determine the required ratings for electrical equipment to adequately sustain the fault current capacity of the system. If a short circuit occurs, the electrical power system’s available energy is directed to the point of the fault in amounts that greatly exceed the normal operating currents, and the equipment must have the ability to withstand and interrupt these large currents until the protective device opens to clear the faulted portion of the circuit.
Protective Device Evaluation:
This evaluation determines if the equipment ratings needed to sustain the fault currents calculated by the Short Circuit Study are adequate. Each circuit breaker, bus, etc., is reviewed in regards to the available short circuit to determine that the equipment can adequately withstand the fault current.
Protective Device Time Current Coordination Study:
The study reviews the relay and circuit breaker trip settings, fuses, and their operating time and current characteristics in order to properly coordinate these settings with upstream and downstream devices so that any faults are isolated to the location of the fault; hence, limiting the impact to the remaining portions of the system. The coordination study is used in an Arc Flash study to determine the length of time an arc would occur which is directly related to the incident energy associated with an arc flash event.
The Hazard Analysis will identify the locations which require PPE greater than Category 0. The review determines if there are possible arc flash mitigation recommendations that can be implemented to reduce the incident energy levels. Such recommendations might include device setting changes, replacement of molded case type circuit breakers with static trip type circuit breakers, changing fuse types, or installation of additional fused disconnects or circuit breakers. As a result of reducing the incident energy levels, the corresponding Category of PPE required to work on the equipment while energized is reduced.
Prevention: Take Action
In addition to addressing your hazard analysis, you should continue to make proper maintenance, training, and care a priority. Always complete regular maintenance on your equipment. Use proper signage and labeling where necessary. Provide your teams with proper safety equipment– like appropriate arc flash suits and fire resistant attire as well as PPE gear. And lastly, don’t forget to make arc flash training a part of your facility safety plan. It’s not enough just to have the information- make sure you do something with it too.
Know your codes:
The National Fire Protection Association Guidelines (NFPA 70E - Standard for Electrical Safety in the Workplace) provides direction to require facility owners to perform an arc flash risk assessment prior to allowing a worker or contractor to perform a task on energized equipment. The arc flash risk assessment identifies the presence and location of potential hazards and provides recommendations for PPE, boundaries for limited and restricted approaches, recommendations for flash protection, and safe work practices. NFPA 70E, ARTICLE 130.5 says an arc flash assessment must be completed to determine if an arc flash hazard exists, taking into consideration the design of the overcurrent protective device, its opening time, and its condition of maintenance. The assessment must be updated if a major modification or renovation takes place, and it must be reviewed periodically, at intervals not to exceed 5 years.
#ProblemSolved: Our Electrical Engineering team is here to help. Send an email to Seth Nace, PE, LC, LEED AP, Manager of Electrical Engineering at seth.nace@ssmgroup.com, or Emerick Martin, PE, Technical Manager of Electrical Engineering at emerick.martin@ssmgroup.com