SAFETY | When the Arc Strikes
Jerry Plank
While this column typically highlights fire and/or electrical shock hazards produced by lighting products, I want to address a hazard whose severity is frequently underestimated, despite posing a significant danger when working with electrical panelboards. Electrical panelboards are used in every lighting project to distribute power safely to products with a series of internal circuit breakers designed to protect each circuit from creating a potential fire from a short or overloaded circuit. While many of us don’t install or service electrical panelboards, at some point you will be in proximity to an open panelboard being serviced on a job site and should stay alert to the extremely hazardous condition known as “arc flash.”
“When arc flash occurs in a panelboard, often there is a plurality of bad decisions that have taken place.”
Arc flash occurs when an electrical fault allows current to jump from points of opposite polarity or across an air gap involving energized contacts or parts shorted to ground. The subsequent result of an arc flash produces intense light that is up to 35,000 deg Fahrenheit with an explosive pressure wave vaporizing metal, causing severe burns, burnt clothing, and destruction of the electrical panelboard or its internal components. The arc created during the electrical explosion can easily project a ball of flame as far as 3 ft. During an arc flash, man-made fabrics can become engulfed in fire, causing clothing fabric to be embedded in the skin.
Like any electrical accident, however, there is usually a series of negative actions that need to occur first. The National Transportation Safety Board, a federal agency of the U.S. that investigates airline crashes, describes an aircraft accident as rarely being caused by a single event but rather a chain of deep, underlining systemic failures, which is analogous to the field of electrical accidents. When arc flash occurs in a panelboard, often there is a plurality of bad decisions that have taken place. The latest safety advisory by the Occupational Safety and Health Administration (OSHA) now includes low voltages of 120 and 208 volts as having sufficient energy to cause harm to workers.
Causes of arc flash run the gamut of loose or unsecured wires and connectors, dust collected in the equipment, improperly maintained equipment, faulty circuit breakers and/or equipment, stripped screws on terminations, missing or damaged wire connectors, conductor insulation damaged during installation, or conductive tools inadvertently shorting contacts, to name a few faults.
If you find yourself in proximity to an open panelboard being serviced in the field, which many of us have, the threat of being injured is possible under the right circumstances. In November 2024, OSHA issued Fact Sheet 4475 – Electrical Safety: Common Electrical Work Myths Card, which describes lowering the threshold to 120/208 volts, as field experience has shown that accidents have not decreased since the arc flash issue was first discussed.
A recent OSHA bulletin advises workers to de-energize panelboards; however, there are certain situations and locations that may not be easily accommodated such as in a store or hospital where normal working hours are extended. Electrical personnel should be qualified to conduct the work and wear arc-rated personal protective equipment required for the voltage present as well as use insulated tools when servicing circuit breakers or other internal electrical connections.
The good news is that panelboards manufactured since 2002 are required to be marked addressing the arc flash hazard per the National Fire Protection Association (NFPA) 70 per Section 110.16. For those made prior to 2002, there is a good chance that these older panelboards will not be labeled, but they must also be treated with the same level of caution to mitigate the arc flash hazard. A quick search on the Internet for a video showing the power of an arc flash will demonstrate just how horrific the hazard can be.
Remember: as both the system’s current and working voltage increase, the intensity of a potential arc-flash event also increases. Always stay alert to electrical hazards when working around panelboards and use proper precautions to protect yourself from injury.
Jerry Plank, LC, is the CEO/founder of Wilger Testing, an accredited third-party laboratory testing for product safety and performance.
