Prioritizing Electrical Safety when Designing Power Distribution

When it comes to electrical safety, the cost is too high to cut corners.

By: David C. Hernandez, Contributor

Picture this: you are a maintenance electrician with 25 years of experience working at a 650,000-square foot industrial facility somewhere in the United States. Your personal safety record is impeccable, and you are respected by your superiors and colleagues.

Today, you are tasked by your supervisor to de-energize a branch circuit off the main switchgear to perform maintenance on a motor control center (MCC). So, you enter a main power distribution area with a 5,000 KVA transformer operating, then you trip the disconnect switch that is on the electrical switchgear of the main service. But the switchgear has not had routine preventative maintenance in over fifteen years. Sadly, and tragically, an arc flash incident occurs upon tripping the disconnect switch and 120 cal/cm incident energy is expelled. In less than two seconds, you are engulfed in flames. The personal protective equipment (PPE) you are wearing is a 40-cal suit, which is industry standard. And that is a problem because your last line of defense against electrical arcs with the highest temperatures known to occur on earth – up to 35,000℉ – is inadequate PPE. The result: You are killed.

If that example sounds alarmist, that is because it is meant to call attention to a danger that thousands of industrial and commercial facilities throughout the U.S. and the world continue to have. This, and similar arc flash incidents, are much more common than most may think.

Consider these facts:

• According to OSHA, there are five to 10 electrical incidents in the U.S. every day.
• At least one of those incidents results in death. That means approximately 365 workers are killed per year in electrical incidents.
• More than 2,000 Americans are treated for arc-related burns every year.

These electrical incidents are largely preventable. In fact, approximately 66% of electrical injuries are the result of human error. We can address some of that problem with much better worker training, maintenance, and arc flash studies. But while workplace mistakes are inevitable, the errors are not only made by onsite workers at the time of the incident. The original engineers of these facilities, many of which are several decades old, also erred by prioritizing financial concerns over employee safety. Sadly, that mindset is well represented today in the planning and designing of modern facilities, and we are subsequently creating safety issues because of the electrical architecture of each plant or facility.

It is the same pattern: Engineers focus on bringing their facilities online as quickly as possible, which means they purchase less expensive equipment to reduce lead times and place that equipment in areas vulnerable to electrical and arc flash events. It is easy to understand why. Bringing the facility online the soonest possible means investors earn a return faster and the company is closer to turning a profit. Equipment that arrives at the facility and is installed faster also helps that cause. But what is most concerning for an electrical safety professional, such as myself, is the placement of that equipment, which is carrying very high incident energy.

Far too often, service equipment is located too close to the utility, which significantly increases hazard risk and likelihood of occurrence. The further a worker is from the source of electrical energy, such as a utility transformer, the lower the incident energy is and the lower the available fault current is. However, this is rarely considered during the design phase. Instead, many in the industry choose to reduce the distance of feeder cables and conduit in order to lower the costs of labor and materials.

The goal should be the opposite. Engineers should always design power distribution in a way that lowers the incident energy because that lowers the arc flash hazard risk. If they did this, they would create a safer work environment.

Designing for less risk

We should all be more cognizant of what can happen during an arc flash incident and perhaps if we were, more emphasis would be placed on worker safety.

No one should design a facility that exposes workers (such as the one in our earlier example) to the possibility of their PPE being vaporized, of having the worker suffer fatal burns, serious bodily injury from shrapnel, loss of hearing, or in the worst-case scenario, death.

What can our industry do? The first two steps are to (1) acknowledge the danger of not acting swiftly to significantly reduce the risk of an electrical incident and (2) decide to follow the Hierarchy of Risk Controls per NFPA 70E, which concludes “elimination,” or physically removing the hazard, is the best path forward. That means designing facilities that do not have high energy equipment placed in the areas where electrical workers will often perform energized work. Industry planners and designers should focus on mitigating electrical hazards. We can choose the following mitigation techniques:

• Outdoor utility service equipment removing high incident energy from the inside
• Protective relays for remote de-energization of high energy equipment
• Adequate feeder distances to lower available fault current
• Current-limiting fuses that reduce incident energy
• Electronic-trip breakers with fast fault clearing times that reduce incident energy

But to have more of the plants and facilities that will be designed and coming online in the 21st century implementing the above mitigation techniques will take a shift in mindset.

Our industry should focus much less on costs and optimize electrical safety. Arc Flash studies should be incorporated as an essential expense for any future facility. These comprehensive reviews will help improve its design and focus on safety rather than cost.

In addition, the safest equipment should be purchased regardless of whether it is more expensive. We should not be installing equipment that will simply pass code. Your workers should have assurances that no expense has been spared to keep them safe.

If our industry takes these steps and implements these recommendations, the U.S. will have safer workplaces, happier workers and set a global standard for excellence in design and safety.

Dave Hernandez, PE, CEM, GBE, CESCP is a distinguished professional engineer licensed in 52 states and territories. He is the Founder & CEO of DCH Electrical Consulting LLC, a world leader in the Power & Energy sector. He has held responsible charge of over 25,000 electrical projects, sits on various industry committees, and has authored several publications.