A Catch-22 occurs when circumstances emerge that place one in a no-win situation; let’s take a look at an arc flash safety Catch-22. The best way to eliminate an arc flash hazard is to place electrical equipment into an electrically safe working condition, which requires interaction with the equipment, which may create an arc flash hazard, which is what we are trying to eliminate.
Confused? You’re in good company!
First off, what is an arc flash hazard? The 2009 edition of NFPA 70E, Standard for Electrical Safety in the Workplace, defines an arc flash hazard as “a dangerous condition associated with the possible release of energy caused by an electric arc.”
Just below this definition is a fine print note that further states: “An arc flash hazard may exist when energized electrical conductors or circuit parts are exposed or when they are within equipment in a guarded or enclosed condition, provided a person is interacting with the equipment in such a manner that could cause an electric arc.”
I am sure most people would agree that being exposed to “energized electrical conductors or circuit parts” is a hazard. However, what about the words “when they are within equipment in a guarded or enclosed condition” and the phrase “provided a person is interacting with the equipment in such a manner that could cause an electric arc?”
What if I am about to rack out (remove) a drawout circuit breaker or open it as part of the process to establish an electrically safe working condition? Is the operation of the breaker considered “interacting with equipment”? Yes. Does an arc flash hazard exist even when the breaker is behind the equipment’s closed door, i.e., “a guarded or enclosed condition”? Yes (unless it is arc-resistant equipment). Don’t I usually have to operate the equipment in order to create an electrically safe working condition? Yes.
Is it logical?
To understand the logic behind this Catch-22, we must take a look at a few underlying problems. What if the equipment fails while operating (interacting with) it? Although a failure of this nature may not be a common occurrence, it can and does happen; an arc flash could result.
The second problem is that anyone working within the arc flash protection boundary (AFPB) must wear appropriate flame-resistant clothing and associated personal protective equipment (PPE) when an arc flash hazard exists. Otherwise, they must stand beyond the AFPB. Unfortunately, operating equipment usually requires being up close.
The third problem is that most electrical equipment enclosures are not designed to contain the energy from an arc flash. In fact, depending on the severity of the arc flash, equipment doors can be blown open unleashing its destructive power.
Assume it is live!
It is not as bad as it sounds. The solution to this Catch-22 is straightforward. Until each step of establishing an electrically safe working condition has been completed, treat the equipment as if it is still energized and dangerous. This means appropriate flame-resistant clothing and PPE must be worn during the entire process and can only be removed after the electrically safe working condition has been created.
What if the prospective incident energy is quite high? Is there an alternative to wearing flame-resistant clothing and PPE, especially the bulky arc flash suits? Yes! Many electrical equipment manufacturers have developed arc resistant equipment, such as switchgear and motor control centers. This type of equipment can contain the arc flash energy behind the enclosure’s doors and redirect it out of harm’s way.
Quick, hand me the remote!
Arc resistant equipment might be great for new installations, but what if the facility’s newest equipment is vintage 1975? Older equipment can still be a problem, especially if the incident energy is high. One solution would be to operate the equipment by remote control. Several devices are available that can automatically rack a circuit breaker in or out as well as perform many other functions, such as operating a breaker’s pistol grip.
The concept is actually quite simple. A device is attached to the electrical equipment, and the remote control allows the operator to stand back by 20 to 30 feet, which is well outside of the AFPB. At this distance, the equipment can be operated more safely to establish the electrically safe working condition.
So much for the Catch-22.
PHILLIPS, founder of www.brainfiller.com and www.ArcFlashForum.com, is an internationally known educator on electrical power systems. His experience includes industrial, commercial and utility systems, and he is a member of the IEEE 1584 Arc Flash Working Group. Reach him at email@example.com.