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. For more information please contact your local Irby branch or visit www.irby. com/services.

Test tool inspection and maintenance

Like all PPE, test tools and associated test leads, cables, power cords, and probes must be regularly inspected and maintained.

Look for the 1000 V, CAT III or 600 V, CAT IV rating, a “double insulated” symbol, and approval symbols from CSA, UL, CE or TUV.
Only use fuses specified by the meter manufacturer.
The second edition of IEC/ANSI/CSA standards states that test equipment must perform properly in the presence of impulses on volts and amps measurement functions. Ohms and continuity functions are required to handle the full meter voltage rating without becoming a hazard. Check the instrument’s manual to verify that the ohms and continuity circuit is protected to the same level as the voltage test circuit.
Check the overall condition of the meter or tester. Look for such problems as a broken case, worn test leads or a faded display. Use the meter’s own test capability to determine whether fuses are in place and functioning properly:

Step 1: Plug test lead in V / o input. Select o.
Step 2: Insert probe tip into mA input. Read value.
Step 3: Insert probe tip into A input. Read value.

Verify test leads are certified to a category that equals or exceeds that of the meter or tester.
Verify leads have shrouded connectors, finger guards, CAT ratings that equal or exceed those of the meter, and double insulation.
Inspect leads for frayed or broken wires. The length of exposed metal on test probe tips should be minimal. Test leads can fail internally, creating a hazard that cannot be detected through visual inspection. Check test lead resistance for internal breaks:

Step 1: Insert leads in V / o and COM inputs.
Step 2: Select o, touch probe tips. Good leads are 0.1 - 0.3 o.

Reprinted with permission by Fluke. Written by Leah Mathias, Editor for Fluke publications.