Arc Flash Relays: A Critical Component of Your Mitigation Strategy

By Ralph DeLisio, Contributor

Opening a door, removing a cover, and operating a disconnecting means or a closing contactor are frequent actions triggering an arc flash

Every day it is estimated between 5-10 arc flash incidents occur in the U.S., according to the U.S. Bureau of Labor Statistics. That is approximately 1,800 to 3,600 each year. Most occur when something is moving. Opening a door, removing a cover, and operating a disconnecting means or a closing contactor are frequent actions triggering an arc flash. A worker’s movement (even a rodent’s movement) might result in an arcing fault.

The intensity of the energy generated in an arc flash depends on the capacity of the circuit to maintain the arc, the duration of the arc, and the distance between the worker and the arc. Arc flashes can range in current from a few amps up to thousands of amps and are highly variable in strength and duration. An arc flash and ignition of flammable clothing are the cause of up to 80% of all electrical injuries and fatalities among qualified electrical workers, according to OSHA. Clothing can be ignited from ten feet away, and clothed areas can be burned more severely than exposed skin.

Need For Rapid Detection

Even if personnel injuries are avoided, an arc flash can damage or destroy equipment, resulting in costly replacement and prolonged and expensive downtime. To prevent serious injuries, fatalities, and property damage, it’s important to have arc flash protection. The best way to minimize the impact of an arc flash event is to reduce the detection and circuit breaker tripping times. Conventional protection may need several cycles to detect the resulting overcurrent fault and trip the breaker. In some cases, there may not be sufficient current to detect an overcurrent fault. Tripping may be delayed hundreds of milliseconds for sensitivity and selectivity reasons in some applications.

Arc flash detection-based (AFD) protection can act on the circuit breaker in a few milliseconds (2–5 ms). This fast response can limit the arc flash energy, preventing injury to personnel and limiting or eliminating equipment damage. The arc flash protection option in one arc flash relay currently on the market adds four-channel fiber-optic AFD inputs and protection elements. Each channel has a fiber-optic receiver and an LED-sourced fiber-optic transmitter that continuously self-tests and monitors the optical circuit to detect and alarm for any malfunction.

Because the relay is always active and monitoring the system for an arc flash, a facility does not have to rely on someone activating the system before doing work, which removes the potential for human error. Studies indicate up to two-thirds of electrical injuries are caused by human error.

In the 2018 edition of NFPA 70E, a guideline was added stating that human error must now be considered as part of the risk assessment procedure and the risk assessment must address the potential for human error and its negative consequences on people, processes, the work environment, and equipment.

Error precursors can involve excessive task demands, the work environment, individual capabilities that are not equal to task demands, and the natural limitations of human performance that cause workers to err under unfavorable conditions.

The propensity for human error is why the NFPA 70E 2018 edition emphasizes engineering out electrical risks. Wearing personal protective equipment (PPE) is the last line of defense. The focus is on how you mitigate the hazard. An arc flash relay is an important part of your mitigation strategy.

Selection factors

Many arc flash relays are available in the market, making it challenging to select and install the right option. What features should you consider?

Reaction time: The relay’s trip speed is an important feature. Reaction times are principally a function of the arc flash relay’s light sensor input sampling scheme and the design of its trip output circuit. Because light is the earliest detectable indication that an arc flash is occurring, arc flash relays use optical light sensors to detect the arc that is forming. One arc flash relay on the market is configured based on monitoring system current, as well as light via fiber optic cables installed in the equipment. This arc flash relay design is capable of also monitoring voltage and data logs and provides other system protection such as undervoltage and ground fault. Ground fault detection allows you security in knowing your systems are ground correctly and you won’t get faults — triggers that will come up.

Trip reliability: Reliable tripping is important because reliability ensures mitigation of an arcing fault.

Installation: Here are key issues to consider regarding installation: Where are you going to locate the relay? How are you going to wire it into your system? You want to have enough flexibility in your installation plans so the closer you can get the relay to your incoming load the less wire runs you have to put out. It is a significant time-saver when you’re not running conduit and you’re not going through ceilings.

You’re always under a time constraint with a shutdown. You want to do your prep work and do a pre-check before you shut down. If you’re running conduit lines, you want to run those wires and conduit long before you shut down. Don’t overlook the importance of pre-work. Finishing the installation and getting the system back up while still having time to troubleshoot if necessary is key. Installing a prefabricated enclosure that is easier to wire to, and getting it as close to the switchgear as possible are two other installation considerations.

What you need to know

Arc flash relays are complicated devices. How much knowledge should a facility safety manager have of an arc flash relay?

You need to know the features and the advantages of these devices. Not every safety manager is an electrical engineer or an electrician. But you need to understand the function the arc flash relay plays, and what it is protecting: these are fundamentals. Work with your electricians or a company that you believe has the right expertise and select a service provider that meets your needs. The right company will understand your requirements, do the pre-work, and install protection correctly.

What should facility managers look for in a service provider?

Emphasize experience. How many arc flash relays has the service installed? In what type of locations? How many relays do you need in a single location? How many crews can a service provider run at once? In a large facility, one service did an installation in a day and evening with nine incoming feeds. There were 42 people on site. Services need to have the ability to manage a large facility, or on the other hand, be able to quickly handle one incoming feed in a short shutdown window.

The pre-work is an important part of all this. And take advantage of other installation options. While you’re installing a relay, it’s a good time to install infrared windows because you have the line side open. When you are infrared testing, you no longer have to open the panel, you can still look at your incoming.

An arc flash relay is critical to prevent serious injuries, fatalities, and equipment damage and downtime.   But your service provider should know what other problems your system may have and correct them proactively and routinely to extend the lifecycle of your assets and improve your operational and safety performance in the long-term. Before your facility enquires about arc flash relay installations, work with a service provider to conduct an arc flash hazard assessment. An assessment can uncover issues in an electrical distribution system that may be hidden and make recommendations for reducing incident energy. If there are issues with your equipment, a service provider will partner with your facility to correct and repair them. One important defense is to install arc flash relays. ESW

Ralph DeLisio is Executive VP at SEAM Group (www.seamgroup.com). He is responsible for creating and maintaining a unified sales strategy across all business units on a global basis. He has more than 25 years of domestic and international business management and sales experience in manufacturing and service development.