Stuart C. Irby Co. : Electrical Distributor

Arc Flash Protection

Protect Yourself from Arc Flash

In North America, an arc flash explosion sends victims to the burn unit five to ten times a day. An arc flash sends concentrated radiant energy, hot gases and melting metal outward at 5,000 to 35,000 degrees Fahrenheit – that’s hotter than the sun. Electrical technicians caught in an arc flash may suffer severe radiation burns, damaged eyesight from the brilliance of the flash, and hearing and brain damage from the accompanying pressure waves of up to 2,000 pounds per square foot.

How arc flash occurs

An arc flash is most often caused when a transient overvoltage happens during a measurement. Transients are electrical surges or spikes caused by reactive loads (motors, capacitors and power conversion equipment such as variable speed drives), lightning strikes, or problems in the electrical system. Transients that ride on high energy circuits are the most dangerous because these circuits can deliver large currents.

When such spikes occur while measurements are being made, they can cause a plasma arc to form — inside the measurement tool, or in the air outside (see Figure 1).

Arc flash can also occur from the misuse of multimeters. If the user leaves the test leads in the amps input terminals and connects the meter leads across a voltage source, that user has just created a short through the meter.

Standards for protection

The National Fire Protection Association (NFPA) 70E, Standard for Electrical Safety in the Workplace (2004) requires calculating a flash protection boundary inside which workers must be protected with personal protective equipment (PPE), such as eye and hearing protection, insulated hand tools, insulated gloves and fire resistant clothing. This boundary is different for various types of equipment and depends in part on the voltages involved.

As an integral component of PPE, test tools and equipment must also meet safety requirements. These standards are established by such organizations as ANSI (reference S82.02), the Canadian Standards Association (CSA), and the International Electro-Technical Commission (IEC).

Regular maintenance

In addition to using test tools and protective gear rated for the electrical work environment, you should also regularly check the equipment in your facility for poor connections, insulation failure, harmonics, overloading and wiring mistakes. All of these can trigger electrical fires and arc flash incidents.

Additionally, the use of thermal imagers can quickly spot hot loose connectors on energized, operating equipment, especially in comparison to cooler, tight connections. Use a megohmeter to measure insulation resistance between phase conductors and between phase conductors and ground conductors. Check long lengths of cable, transformer windings, and motor windings. Good insulation should have very high resistance. Low readings can indicate the cable is breaking down, potentially causing a short.

Periodic power quality studies will alert you to potential problems due to excessive harmonic current, voltage sags caused by deteriorating connections, and many other wiring problems.

Protecting yourself from arc flash comes down to respecting the danger, following safety procedures and maintaining your equipment.

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