Potential causes of an Arc Flash or Arcing Fault may include:

• Workers mistakenly dropping tools on live parts
• Pests entering switchgear through openings
• Faulty operation of a load break switch
• Dust or moisture accumulating to weaken air insulated bus bars
• Improper use of test equipment

From personal experience onsite and reading incident reports, the last three are the ones that are mostly likely going to be the cause of an Arc Fault.

Faulty Switches

Within an utility, institutional and industrial setting, electrical equipment does not always get the proper maintenance that it requires to have optimal operation.  With age, the ability of these mechanical devices to extinguish faults diminishes causing potential catastrophic failures

Electricians have been trained for a very long time to operate these breakers, switches etc from an arms length distance to the side.  This minimizes their body exposure to a possible failure.

Dust and Moisture

Industrial facilities such as refineries, pulp and paper plants, etc are not very clean environments, and as such there is a risk that there will be faults with electrical equipment due to the build-up of dust or introduction of moisture within the enclosures.  Modern company standards for electrical rooms have reflected this with the introdction of solid-state drives that are not as forgiving to dusty environments, and as such the new electrical equipment rooms are typically under static pressure to better control the enviroment.  PotashCorp of Saskatchewan is an example of one of the companies that are following this methodology.

This said, there are many existing electrical rooms that remain without such methodology.  To ensure that employees that usually work in these rooms are at the very least moderately protected, one company that I have worked with has a standard practice that anyone working in these rooms must wear 8 Calorie/cm² coveralls and safety glasses.  This level of PPE meets the majority of Incident Energy Levels within the electrical rooms in that facility.

Improper Use of Test Equipment

In the modern maintainence and operation of facilities the governing philosphy is to do all work on electrical equipment only after it has been grounded and isolated from the system.  This ensures that it is at a zero energy state and the risk of electrocution is minimized as much as possible.

There are still a number of situations that this is simply not practical, the most often offender being during commissioning or trouble shooting.  These activities most often requires the worker to test the voltage of the equipment to ensure they match the expected values.  With older test equipment, and cheaper modern equipment, there is a risk that the worker will not have the test equipment set properly.  If they try to check the voltage of a busbar while the meter is set for current, it acts like a short circuit and this will cause a fault that may lead to an arcing fault, which may lead to an ingury to the worker or people standing by.

What can you do.

One of the things that you can do to help mitigate a serious injury is to wear the correct PPE when working on equipment that has not be verified to be at a zero energy state.  Recent standard releases within North America (NFPA 70E in the US, and CSA Z462 in Canada) the level of PPE required when the possible incident energy is known.  If the levels are not known, speak with your managers and ask them to inform you of what the levels are.

When planning to work on live equipment, ensure that there is a job plan and everyone knows what their roles will be and what the emergency plan is.  With a comprehensive emergencuy plan an incident has a better chance to be contained and not excalating to harm others.