Arc Flash Consultants

What is Arc Flash ?

Arc Flash is the result of a rapid release of energy due to an arching fault between a phase bus bar and another phase bus bar, neutral or a ground. During an arc fault the air is the conductor. Arc faults are generally limited to systems where the bus voltage is in excess of 120 volts. Lower voltage levels normally will not sustain an arc. An arc fault is similar to the arc obtained during electric welding and the fault has to be manually started by something creating the path of conduction or a failure such as a breakdown in insulation.

Arc Flash Risk Assessment

what is Arc flash risk assessment? is the primary question in every safety professional mind. Understanding Arc flash hazard risk category charts and Arc flash limited approach boundaries and incident energy analysis and its related Arc flash boundary tables looks little technical subject but in practical its more of safety and easiest way of avoiding disasters.

Why is an Arc Flash study needed?

There are a number of codes that all address arc flash study evaluations and why they are required. I’ll list them in the next blog post but first a brief explanation of what an arc flash hazard is and why it’s so dangerous.

Arcing from electrical equipment can produce extremely high temperatures. They can exceed 30,000 degrees Fahrenheit, which is hotter than the surface of the sun. An arc flash occurs when a rapid release of energy due to an arcing fault between a phase bus bar and another phase bus bar, neutral or a ground bar occurs. During this type of fault, air becomes the conductor and it expands dramatically. This causes metal conductors to vaporize and can cause an intensely hot blast. The danger lies when employees are working on electrical equipment and are not wearing adequate Personal Protective Equipment (PPE). Workers can be seriously injured or killed when an arc occurs.

Designing for Electrical Shock and Arc Flash Safety

The PPE (Personal Protective Equipment) requirements to work on live electrical equipment is making commissioning, startup, and tuning of electrical control systems awkward and cumbersome. We are at a stage where the use of PPE is now required but practice has not caught up with the requirements. While many are resisting this change, it seems inevitable that we need to wear proper PPE equipment when working on any control panel with exposed voltages of 50 volts or more.

With many electrical panels not labeled for shock and arc flash hazard levels, the default PPE requires a full (Category 2+) suit in most cases, which is very awkward indeed. What can we do to allow us to work on live equipment in a safe manner that meets the now not so new requirements for shock and arc flash safety?

Here is one thought to improve electrical shock and arc flash safety by designing this safety into the electrical control panels.

Keep the power components separate from the signal level components so that maintenance and other engineers can work on the equipment without such hazards being present. That’s the principle. What are some ideas for putting this into practice?

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  • Run as much as possible on 24VDC as possible. This would include the PLC’s and most other panel devices. A separate panel would then house only these shock and arc-flash safe electrical components.
  • Power Supplies could be placed in a separate enclosure or included in the main (low voltage) panel but grouped together and protected separately so that there are no exposed conductors or terminals that can be reached with even a tool when the control panel door is opened.
  • Motor Controls running at anything over 50 volts should be contained in a separate enclosure. Try remoting the motor controls away from the power devices where possible. This includes putting the HIM (keypad) modules for a VFD (Variable Speed Drive) for example on the outside of the control panel, so the panel does not have to be opened. Also, using the traditional MCC (Motor Control Centers) enclosures is looking increasing attractive to minimize the need for PPE equipment.
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