July 4, 2018
By Jeson Pitt, D&F Liquidators
Arc flashes can be used to describe low impedance connections in an electrical system. It is a high-amp current that jumps through the air and occurs when the path of the electric current is interrupted. When this happens, the current flows through the air to a new conductor or the ground which causes a very bright flash of light.
This leads to a rapid rise in temperature and pressure in the air between the two electrical conductors and causes an explosion. The arc blasts and the resulting heat leads to fires, flying shrapnel and pressure waves, causing serious damage to life and property within the boundary of the arc flash.
Causes of Arc Flashes
An arc flash occurs when several electrical conductors are placed close to each other, with significant fault currents flowing through them. This causes ionization of air to take place as a result of numerous factors like potential difference, leading to a low resistance path. This allows current to flow through the air gap between conductors.
Other causes include:
• Improper use of tools, work techniques or equipment installation;
• Obstruction in disconnect panels;
• Carelessness of employees or accidents like touching the wrong surface with a test probe;
• Exposure of construction electrical products to water and liquids;
• Wear and tear of equipment;
• Lack of electrical safety awareness and training;
• Improper preventative maintenance for circuit breakers and switches; and
• Exposed live parts, loose connections or corrosion.
Three Tips to Protect Workers from Arc Flashes
If your equipment is more than a decade old, then it is an arc flash disaster waiting to happen. There have been several technological developments in the past ten years that have improved the management of arc flash’s potential danger. Update equipment older than ten years. Once you upgrade the equipment, you can reduce the arc flash risk in the installed infrastructure, increase the life of capital equipment and improve overall safety.
Arc flash containment aims at capturing and dispersing the effects of an arc flash within the hardened equipment. Mitigating arc flash is better than this technique due to numerous reasons like containment equipment getting destroyed while capturing arc flash or the equipment being large, heavy and difficult to work with.
• Use Lower Short-Time Delay Bands: Use trip units that have lower short-term delay times. By lowering the delay times, you can reduce the time it takes a circuit breaker to trip by up to 50 per cent, thus cutting down the energy in an arc flash event.
• Instantaneous Zone Selective Interlocking: Instantaneous Zone Selective Interlocking (I-ZSI) protection delivers safety and selectivity against arc flash energy. This innovation re-thinks the total system and places the main circuit breaker on an alternate setting if a fault occurs below the feeder. This allows you to stay up and running at all times. I-ZSI case studies report that arc flash energy can be reduced to just 18 per cent –25 per cent of the energy released during events as compared to traditional ZSI or staggered protection.
• Use Reduced Energy Let-thru: Reduced Energy Let-thru (RELT) is a safety window. Most of the new digital trip units offer two separate instantaneous set points, allowing the workers to lower the trip threshold with the flip of a switch before servicing energized equipment. This helps in lowering incident energy potential.
• Retrofit Fuse-Technology Load Interrupter Switches: If you have older equipment, they might use fuses to cut power in load interrupter switches on distribution transformer primaries. These fuses can take up to half a second to respond — which is a long time in the event of an arc flash. By retrofitting fused interrupter switches with modern circuit breakers, it will be possible to cut off power in 3 cycles (3/60 of a second), which limits the arc flash time by a great degree and reduces its energy significantly.
• Arc Mitigation with Energy Transfer and Containment: You can also opt for a new arc containment technology which uses arc-to-arc transfer to keep the energy low and allow fast mitigation. This hybrid solution has the ability to stop an electrical fault in 7 milliseconds or less, mitigating the fault while also transferring the energy into a hardened containment dome.
The hardened system shuts down the flash and absorbs the energy quickly, sustaining very little damage during an arc flash event. This solution delivers a greater return on investment while reducing downtime, improving productivity and lowering the risk of injury.
Arc flash mitigation technologies and strategies should be part of the design for new electrical systems as well as retrofits.
Jeson Pitt works with the marketing department of D&F Liquidators and regularly writes to share his knowledge while enlightening people about electrical products and solving their electrical dilemmas. Jeson lives in Hayward, Calif.