Arc Flash & Electrical Safety News

Blog Author Steve Hudgik

Wednesday, December 19, 2007

Isolating the Risk of Catastrophic Arc Flash Explosions

Betty Jackson, of Hoffman, has publish a white paper titled "Isolating the Risk of Catastrophic Arc Flash Explosions" that is available online. This paper makes that point that arc flash incidents will happen and that a solution is the Hoffman SEQUESTRâ„¢ External Disconnect Enclosure.

The paper begins by providing an overview of arc flash, its causes and the damage that can result. It gives this summary of arc flash hazards:

"According to NFPA 70E Standard for Electrical Safety in the Workplace, 2004 Edition, pages 12 and 28, the two most important numbers to remember are 1.2 and 40. Incident energy levels greater than 1.2 calories per centimeter-squared can produce second degree burns. The NFPA 70E requires that workers wear personal protective equipment (PPE) when working with 50 volts or more. Arc flash levels above 40 calories per centimeter squared can be fatal and usually result in a massive pressurized blast with sound pressure waves and projectiles. The PPE is available for exposures up to 100 calories per centimeter-squared; however, the force from the pressurized blast can be fatal regardless of the PPE."

The white paper then goes on to point out that in spite of best efforts, because of the large number of variables--some of which may be unknown--the true extent of the arc flash hazard can never be known. In addition, the paper points out something I know to be true from personal experience:

"During private discussions, electrical engineers have revealed that, despite their compliance training, they sometimes skirt the PPE rules because the bulky, fire retardant suit, gloves, face shield/goggles and other gear is hot, uncomfortable and makes service and maintenance time-consuming and cumbersome."

The second half of the white paper dicusses the SEQUESTRâ„¢ External Disconnect Enclosure.

"The SEQUESTRâ„¢ External Disconnect Enclosure attaches to the side of a main control enclosure and houses only the disconnect switch or circuit breaker, physically removing it from the main enclosure."

"Live power is no longer present in the main control enclosure when power is turned off at the disconnect switch. It completely shuts down the power in the main cabinet, and there is no hazard of power coming into the box. Its system also interlocks the doors of the main control cabinet when the disconnect switch is powered on. This allows users to comply with the disconnect door interlocking requirements of UL 508A, NFPA79, IEC 60204, and HS 1738, the most common electrical standards for industrial machinery."


Use the link above to read the entire white paper.

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