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10 arc flash myths

May 26, 2014
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myths1 - Arc flash explosions do not happen… I have never seen one… 

Electrical work by its nature is dangerous due to the high energy levels involved and, until an accident occurs, electricity is odorless, colorless, and invisible. Electrical work is the third most dangerous profession, according to OSHA. An article in Fire Engineering magazine said often arc flash accidents “may occur when you perform routine maintenance.” The likelihood that electricians will complete their careers un-scarred by an arc flash or without knowing an arc flash victim is slim.

2 - NFPA-70E is the standard governing arc flash

Not really. It’s really about reducing live work by de-energizing a circuit first and putting it in an electrically safe condition before starting to work.

3 – Arc flash hazard labeling equals compliance with NFPA-70E

To work on any energized equipment above 50 volts, an energized work permit is required. A work permit is critical and cannot be bypassed by a simple labeling system. Employers and management are directly responsible for work permitting, safety programs, training and planning.

4 - Arc flash analysis is simply panel labeling

 Arc flash analysis is about hazard reduction. It is not merely PPE selection.

5 - Assessing equipment under 240 volts from a transformer rated below 125 kVA isn’t necessary

OSHA regulations and NFPA-70E standards mandate all equipment operating at 50 volts and higher must be tested for electrical shock and potential arc flash hazards. IEEE 1584 states, “Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply.” This only refers to incident energy calculations. Employers must assess all equipment operating at 50 volts and higher for other dangers, including shock and overload conditions, which can cause fire, electrocution, or other hazards.

6 - Regular infrared scans of equipment rule out doing an arc flash analysis

 Arc flash can be caused by equipment failure or loose connections, but most injuries are caused by human error and will only be avoided through regular analysis of equipment, work practices, and safety training programs.

7 - Beyond the Motor Control Center (MCC), it isn’t necessary to check equipment for arc flash hazards

The MCC is the final access point of power for motor loads, but this  doesn’t mean there isn’t a need to assess other loads, which are fed from it.

8 - Current-limiting fuses reduce most arc flash hazards

These fuses don’t thoroughly address the duration component of arc flash. A current-limiting fuse will mitigate arc flash hazards only if the fault current is high enough.

9 - There’s no arc flash hazard if there’s no exposed, energized conductors or circuit parts

For most equipment, the probability of an arc flash may be very low, but it’s certainly not impossible. Inserting or removing draw-out circuit breakers, bus plugs and MCC buckets can cause an arc flash where, normally, there is no perceived hazard — “normally” operating electrical equipment has been known to fail.

10 - Downstream arc flash hazards are always less violent than upstream arc flash hazards

Complete a full assessment both up and downstream. Don’t stop at hazard level 1 or 2 and be the one who finds out the hard way that this dead wrong.

Source: Kevin Meagher, Chief Technology Officer, Power Analytics Corporation

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