Arc flash: avoid the shock

Go beyond the NFPA 70E tables to do an analysis.




An accurate and effective arc flash analysis will take time and money, but it could very literally save someone’s life. Courtesy: JacobsWhether to perform an arc flash analysis is a consideration for managers who have employees performing electrical work at their plant. But the consideration of the cost of performing a full-blown arc flash analysis is often enough to put this issue on a back burner. This is particularly true since managers may think it's sufficient to use the Arc Flash PPE selection tables in the NFPA 70E standard.

But should managers keep relying on NFPA 70E tables?

The reality is that the problem of determining the precise hazard employees face, and what it takes to properly protect them from that hazard is not solved by using NFPA 70E tables. In more personal terms, the problem is ensuring that employees are not burned from exposure to an arc flash event and are able to return home safely each day.

Sure, the NFPA standards do allow the use of the tables. But one must keep in mind that the tables are not an exact science. And let's face it, most employees may not use them properly anyway. It is the managers and employers who must know for certain if employees are protected from arc flash hazard levels at every location of the electrical system.

When industrial or commercial electrical distribution equipment fails, it can potentially result in an explosion. This explosion is the manifestation of incident energy. The only way to know exactly which personal protective equipment (PPE) is needed to protect employees from arc flash hazards is to perform an incident energy analysis.

Electrical system equipment and equipment configuration need to be evaluated to determine how much incident energy-heat generated from the explosion-can be produced during a worst-case failure. Incident energy is measured in calories per centimeter squared (cal/cm2). A calorie is the amount of energy it takes to raise the temperature of one gram of water one degree Celsius.

An arc flash analysis determines the most severe incident energy that can be produced at each location of the distribution system so that there is no doubt what level of arc flash PPE is required to protect workers from being burned during an arc flash event.

Performing an analysis

The first step of an arc flash analysis is data collection. A properly performed analysis requires information about every conductor, disconnecting device, protective device, transformer, capacitor, motor, and piece of electrical equipment associated with the electrical distribution system. Information from the electrical service provider also is needed. After the necessary data is collected, the entire electrical distribution system will be modeled either by hand or in a software program that will then be used to calculate the incident energy at any location where maintenance or operations activities could be performed. Keep in mind that the accuracy and completeness of the information collected and used to model a system will have a direct correlation to the accuracy of the incident energy calculations that will be used to determine the required level of arc flash PPE.

A common mistake companies make is rushing the data collection process and making assumptions just to get stickers on their equipment faster. The problem with this is that the quality of the end product may be impacted negatively because of a desire for a quicker schedule. An accurate and effective arc flash analysis will take time and money, but it could very literally save someone's life.

There are often overlooked side benefits of having an arc flash analysis performed. The analysis will generate a thorough database of electrical equipment, their configurations, and their protective settings. Often the analysis leads to updating existing drawings to include a complete set of accurate one-line diagrams of the entire distribution system.

There also could be the benefit of a having a knowledgeable person from outside the company give advice on changes to help improve the system's efficiency or offer ways to avoid some developing electrical failure. Many people identify equipment coordination issues that can lead to larger outages than necessary when a breaker trips. These are just a few examples that hopefully start to paint the picture that benefits can greatly outweigh the upfront capital investment.

One more step needed

The NFPA 70E requires that the arc flash analysis be reviewed at a frequency not to exceed five years. It also requires it to be updated when any changes are made to the system. There is a key principle to understand related to arc flash energy: it is determined by the available fault current at the location of the fault and the amount of time it takes to clear the fault. Assume there is a fault inside a motor control center and there is a breaker immediately upstream that clears the fault. The arc flash analysis makes the assumption that the breaker will open in accordance with the protective setting design and the contacts will separate at a speed for which it is designed. A poorly maintained breaker eventually will begin to respond more slowly and in extreme scenarios may not respond at all.

In these cases, the arc flash energy levels can greatly exceed levels calculated by the analysis. Therefore, an Effective Electrical Equipment Maintenance Program (E3MP) is an essential part of maintaining an accurate arc flash analysis program.

While it may seem like ensuring that electrical workers are protected from arc flash hazards is a cost that has no end, there are many studies available that verify the return on investment for electrical safety is a profitable endeavor. And let's face it, there is no price you can put on avoiding a phone call to tell someone that his or her loved one has been burned or killed as the result of an arc flash incident.

Tommy Northcott is a senior power engineer with Jacobs.


Top Plant
The Top Plant program honors outstanding manufacturing facilities in North America.
Product of the Year
The Product of the Year program recognizes products newly released in the manufacturing industries.
System Integrator of the Year
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
October 2018
Tools vs. sensors, functional safety, compressor rental, an operational network of maintenance and safety
September 2018
2018 Engineering Leaders under 40, Women in Engineering, Six ways to reduce waste in manufacturing, and Four robot implementation challenges.
GAMS preview, 2018 Mid-Year Report, EAM and Safety
October 2018
2018 Product of the Year; Subsurface data methodologies; Digital twins; Well lifecycle data
August 2018
SCADA standardization, capital expenditures, data-driven drilling and execution
June 2018
Machine learning, produced water benefits, programming cavity pumps
Spring 2018
Burners for heat-treating furnaces, CHP, dryers, gas humidification, and more
October 2018
Complex upgrades for system integrators; Process control safety and compliance
September 2018
Effective process analytics; Four reasons why LTE networks are not IIoT ready

Annual Salary Survey

After two years of economic concerns, manufacturing leaders once again have homed in on the single biggest issue facing their operations:

It's the workers—or more specifically, the lack of workers.

The 2017 Plant Engineering Salary Survey looks at not just what plant managers make, but what they think. As they look across their plants today, plant managers say they don’t have the operational depth to take on the new technologies and new challenges of global manufacturing.

Read more: 2017 Salary Survey

The Maintenance and Reliability Coach's blog
Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
One Voice for Manufacturing
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Maintenance and Reliability Professionals Blog
The Society for Maintenance and Reliability Professionals an organization devoted...
Machine Safety
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
Research Analyst Blog
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Marshall on Maintenance
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
Lachance on CMMS
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
Material Handling
This digital report explains how everything from conveyors and robots to automatic picking systems and digital orders have evolved to keep pace with the speed of change in the supply chain.
Electrical Safety Update
This digital report explains how plant engineers need to take greater care when it comes to electrical safety incidents on the plant floor.
IIoT: Machines, Equipment, & Asset Management
Articles in this digital report highlight technologies that enable Industrial Internet of Things, IIoT-related products and strategies.
Randy Steele
Maintenance Manager; California Oils Corp.
Matthew J. Woo, PE, RCDD, LEED AP BD+C
Associate, Electrical Engineering; Wood Harbinger
Randy Oliver
Control Systems Engineer; Robert Bosch Corp.
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
Design of Safe and Reliable Hydraulic Systems for Subsea Applications
This eGuide explains how the operation of hydraulic systems for subsea applications requires the user to consider additional aspects because of the unique conditions that apply to the setting
click me