Arc mitigation: Reduce threats with a cost-effective arc flash solution

Arc flash mitigation is easier said than done. Until recently, conducting an arc-flash hazard analysis has been difficult. Though significant testing and empirical formulas have been developed, the available algorithms and formulas are still difficult for engineers in offices to solve without the use of a computing tool and nearly impossible for people in the field to apply.

But with increased industry focus on electrical safety, a broader recognition of arc flash hazards now exists. Arc flash is one of the most complicated and dangerous hazards that owners, facility managers, system designers, and consultants work to avoid and contain. It is also one of the most potentially dangerous and destructive forces in the field of electrical installation, operation, and maintenance.

In uncontrolled situations, an arc can generate heat in excess of 35,000 °F and a blast force with pressure waves as high as 1,000 pounds per square foot with high intensity sounds as high as 160 decibels. High velocity projectiles from an arc can reach speeds of 700 mph (1000 fps) and toxic gases can expand by a factor of 67,000, which can cause injury and harm to workers, equipment, and facilities.

Like the arc hazard itself, the steps taken to mitigate the risk are usually complicated and multi-faceted, relying on multiple entities to provide accurate information. Mitigation requires a collaborative effort by the facility owner, system designer, and manufacturer to design solutions. Unfortunately, in a typical design-and-then-build project environment, information is not always readily available or exchanged - be it at the system short circuit level (SCL), the make-up of the electrodes in an electrical gear, the enclosure sizes, or the standard operating procedures of a facility. These many factors can foil even the most well-thought-out solution.

Fortunately, there is a simple, cost-effective solution to defeat arc flash on the line side.

Arc flash mitigation begins with assessing potential risks

Arc flash risks can be engineered out of electrical systems by following a Safety by Design approach during the design and specification stage of a new build or system update. Because human error is a leading cause of an arc flash, engineered solutions that reduce the possibility of accidental contact with energized components are particularly effective.

Arc flash hazard and mitigation is now enforced under the Title 29 of the Code of Federal Regulations (29 CFR) part 1910. This guidance addresses worker safety using two sets of standards: The National Electrical Code® (NEC ) and the National Fire Protection Association (NFPA) 70E ®. Each takes its own approach to defining the standards for electrical safety. The NEC is focused on system engineering, installation, and maintenance while the NFPA 70E covers safe workplace practices. Together, they include specific requirements for reducing the risk and severity of arc flash, as well as the measures that must be implemented to protect people working on or near electrical equipment. Mitigation requires an understanding of arcing current magnitude, arcing current path, and the arc duration. One of the parameters used in quantifying the arc flash hazard is the (arc flash) incident energy level (AFIE). AFIE is the measure of the amount of energy available at a given distance from the arc during an arc flash event.

Many solutions to either eliminate the hazard or reduce the arc flash incident energy rely on removing the source of energy (de-energized work), redirecting the arc energy (arc resistant switchgear), or removing the operator outside of the arc flash boundary. While these solutions help reduce or eliminate arc flash hazard risks to personnel, equipment damage is rarely prevented by these solutions.

Other solutions rely on reducing arc flash hazard by detecting arc faults and then racing to clear them. Relying on upstream over-current protection devices to interrupt arc faults can be risky because they're triggered by sensing light, sound, current or some other by-product of an arc flash. But this sensing equipment often relies on auxiliary power, system design, or operator interventions - and thus introduces the possibility of human error. More importantly, these solutions are one-time use solutions, which then require reconditioning inspection and/or replacement of the equipment or failed components.

How to mitigate threats with always-on passive controls

A passive, repeatable, always-on arc flash control solution does not require complex system engineering. To be effective, it removes operator intervention, does not require auxiliary power, and vastly reduces the risk to both personnel and electrical equipment. Passive arc flash protection systems simplify arc flash hazard mitigation and make arc mitigation strategies much easier to adopt.

The Square D™ ArcBlok™ 2500 system from Schneider Electric™ is one such always-on arc flash prevention and containment system for low-voltage motor control centers (MCC) and switchboards up to 2500 A. The system reduces AFIE to UL 2986-verified levels of less than 1.2 cal/cm² at 18 inches on the line side. Instead of reacting to the arc energy, ArcBlok takes a practical approach to extinguishing the arc by minimizing opportunities for an arc formation. It does so by elongating the arc path and thereby extinguishing the arc.

Inside ArcBlok's arc containment vault, an arc-free module and other barriers work in tandem to reduce an opportunity for an arc, using the approach above. Any sustained arcing current is extinguished in less than one cycle (<16.6ms), which is faster than the reaction of any other active or reactionary protection system.

Unlike most active solutions, no tripping occurs, so there is neither downtime nor interruption of upstream devices - all while keeping the arc fault contained. ArcBlok also isolates the line-side connectors within the cable vault to prevent accidental contact that could trigger an arc flash.

ArcBlok is a simple, Safety by Design solution that accomplishes the four broadly accepted dimensions of safety: reduction, avoidance, prevention, and containment.

Safety by Design is a cost-effective way to protect workers and equipment, because effective arc flash mitigation requires layers of controls that may include:

• Arc resistant equipment
• Infrared monitoring
• Optical sensors
• Plus, in some cases, other detection devices and virtual mains, along with administrative controls and personal protective equipment (PPE) rated for various levels of AFIE
• Specialized skills to properly operate and maintain the inherent complexity of electrical systems

How to simplify arc flash prevention

ArcBlok simplifies arc flash protection during installation, maintenance, and operation. It even simplifies the process of designing electrical systems with arc flash protection. ArcBlok is a self-contained, modular system that is compatible with a wide range of motor control centers and switchboards, and can be installed as part of a main breaker upgrade. It contains no moving parts and requires no special commissioning or costly setup in the field. It ships ready to deploy.

Installation has virtually no impact on equipment footprint. ArcBlok does not require venting plenums or increased ceiling heights or additional HVAC burden due to the increased room sizes.

It's also pre-configured with thermal sensors that eliminate the need for interval-based monitoring and associated costs. The sensors deliver valuable information that can provide historical data to identify problems even before they occur, schedule predictive maintenance, and optimize the system. Although load-side controls such as zone selective interlocking (ZSI) and energy reducing maintenance switch (ERMS) are still necessary, ArcBlok makes very high-line-side incident energy levels. It requires only two levels of PPE or complex arc energy hazard protective devices and schemes devices are unnecessary.

ArcBlok offers more cost-effective arc flash mitigation

Arc-resistant equipment usually requires capital expenditures that are 15 - 30% higher than standard electrical equipment. ArcBlok was designed to provide a better return on this investment for arc flash mitigation and prevention.

For example, while an arc flash usually destroys or significantly damages the associated equipment, ArcBlok is rated to withstand up to five arc events before replacement is necessary, dramatically cutting down on capital expenditures. ArcBlok also significantly reduces the chances of unplanned downtime during repairs or from nuisance tripping.

Although the acquisition cost is roughly 15% greater than standard equipment, significant ROI will accrue over the equipment lifecycle including:

• A reduction in additional arc flash engineering controls
• Lower installation, commissioning, and ongoing maintenance costs
• Reduced need for PPE and associated costs
• Increased productivity and job satisfaction by less time spent donning, doffing, and working in bulky PPE
• Avoidance of direct and indirect arc flash-related expenses, including medical and legal costs, fines, increased insurance premiums, and business continuity interruptions

Protect your business through arc flash mitigation and prevention innovation

Ultimately, the most important ROI measure of arc flash mitigation is worker safety. ArcBlok protects workers by extinguishing arc flashes before they can propagate. Because it is a passive system, ArcBlok dramatically reduces the possibility of human error that frequently causes arc events.

To learn more about how to avoid, prevent, reduce, and contain arc flash, browse our arc flash protection and safety resources here.

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