Two often overlooked steps in an Arc Flash Study are the Coordination Study & Mitigation Strategies. Simply put, these are the steps that actually make the electrical system safer and reduce risks. There are many reasons that companies implement an arc flash study. They can include compliance, corporate policy or even insurance requirements. But let’s not forget the main reason that they are required by NFPA 70E in the first place: To Create a Safer Working Environment and Reduce the Risk for Personnel Working in or Around Live Electrical Equipment.
That is the bottom line. That is our goal: Safety and Risk Reduction. Coordination and Mitigation actually accomplish this goal and reduce the risk. So what exactly is coordination and mitigation? Glad you asked.
A coordination study is a detailed engineering analysis of the electrical system which identifies areas in your system where the over-current protective devices might not open in the proper sequence. Over-current protective devices include breakers, fuses, relays, etc. and are designed to be the last line of defense in the event that a fault occurs in the electrical system. If there is a fault or an arc flash event in a downstream breaker panel, ideally we want the breaker closest to that panel to be the breaker that opens and clears the fault rather than an upstream breaker further away from the incident. This accomplishes two goals: First, the fault is cleared faster. Second, the loss of power is isolated to a smaller area.
In a system that is not coordinated the fault may pass through one or more breakers to an upstream breaker before the fault is cleared. This takes longer to happen and creates much more heat and energy at the location of the fault placing any personnel in a dangerous situation. In addition, the loss of power affects a larger portion of the electrical system.
It is not uncommon to have coordination issues in an electrical distribution system, especially as it ages and changes are made over time. Case in point: a hospital in which we recently completed an arc flash study had a major coordination issue. A problem in a 30 amp breaker far downstream from the main switchgear was causing the Main Breaker (3000 amp) to trip. This is a major coordination problem, and as you can imagine, is not ideal for a hospital. In performing the coordination study for this hospital, our engineers were able to recommend trip setting adjustments on the main breaker to fix the problem. From an operational and safety standpoint this was a huge benefit for the facility. See figure below for details.
It is not uncommon to find dozens of coordination issues inside an electrical system when we provide arc flash studies to our customers. Each one of these issues, when identified and corrected, may reduce the hazard throughout the facility and protect the worker.
Mitigation involves actually reducing the incident energy inside an electrical panel. Incident Energy represents the degree of hazard inside each electrical device and is measured in cal/cm2. The higher the incident energy, the greater the hazard and the more intense a potential arc flash would become. Through mitigation, we can identify the devices that contain high incident energy and explore ways to actually reduce that value.
Let’s look at an example. In conducting a recent arc flash study we analyzed a 480V distribution panel that had an incident energy of 38.2 cal/cm2. This level of energy requires Category IV PPE, which is hot and cumbersome to work in. By performing a mitigation analysis, we were able to identify alternate trip settings to the breaker feeding the panel that would reduce the Incident Energy to 0.7 cal/cm2 which only requires Category I PPE. This is a huge reduction in risk and danger and reduces the arc flash boundary from 12 feet to 12 inches.
Let’s repeat that again.
- Incident Energy was reduced from 38.2 to 0.7
- PPE necessary was reduced from category IV to category I.
- Arc Flash Boundary was reduced from 144 inches to 12 inches.
Any time we are able to reduce the incident energy it creates a safer working environment, reduces risks and makes the job easier for the person doing the work. It is not uncommon for our engineers to find multiple opportunities to reduce the incident energy in just one facility. As a matter of fact, at a recent hospital in Florida, we were able to identify over 50 areas in which we could reduce the hazards from Category III or IV down to a Category I hazard.
A coordination study and mitigation strategy should always be a part of an arc flash study. They are the only steps that can actually identify techniques and changes that will reduce the hazard levels inside your electrical system. It is common for our engineers to identify dozens of areas inside an electrical system that can be made safer through coordination and mitigation, and many times these changes are simple settings on a breaker.
Again, arc flash studies are often implemented as a result of compliance, but let’s not forget what they are designed to do which is save lives and prevent catastrophic injury to workers. An effective arc flash hazard survey that includes a coordination study and mitigation strategy accomplishes both.