Calculating where the boundary will be in any given situation is something that should be done by an electrical engineer.

This is the level at which it will cause only second-degree burns rather than third-degree. It’s not perfect, and remember that there is some limitation to this method, but when you have nothing else it will certainly do.An arc flash boundary is the distance from the equipment in question to the point where the energy that would be present in an arc flash is 1.2 cal/cm2. This article should give you a handle on how to calculate arc flash boundaries. Anyone who is working within the arc flash boundary will still need to be wearing arc flash PPE. Remember, this is only to keep others safe and outside of the electrical boundary. My barricades need to be set up at 2.22 meters or about 7 1/2 feet. How far away do I need to place my barricade? We know from our rule of thumb that this will take 0.1 seconds. So if an arc flash were to occur when I was racking out the feeder breaker then I’m relying on the main breaker to trip. Above that is a transformer with an MVA equal to 10. Let’s say I’m racking out a 5kV circuit feeder breaker that is fed by another 5kV circuit breaker (which I’ll refer to as the main breaker). 5kV to 15kV circuit breaker t= 0.1 secondsĪn example arc flash boundary calculation.current limiting fuse t = 0.004 seconds.This one can be a bit tricky but you can follow these rules of thumb for the most part: T is the time that the arc flash is supposed to last. Note: if the MVA is less than 0.75 you’ll need to multiply it by 1.25 in order for the calculation to work. MVA should be there… or KVA (divide KVA/1000 to get MVA). Go find the transformer and look at the nameplate. MVA is from the transformer that is feeding the piece of equipment you are working on. Now, if you’re not a math wiz don’t worry, stay with me… I’ll walk you through this.ĭc is what we are trying to determine… the arc flash boundary.Ĥ.92 is just a constant… Ralph Lee figured it out, you don’t have to. Like I mentioned before, there are a number of ways to calculate the boundary but the one I’ve chosen as a go-to is the Ralph Lee arc flash boundary formula calculation method ( here is a link to his white paper). You can accomplish this with red or yellow tape, cones, pylons, a stand-by attendant… really any of the traditional ways one would alert someone of a hazard that is not always present. Why do I need it and what do I do with it?ĭuring any electrical job (that will expose people to an arc flash) the worker must set up a barricade at or beyond the boundary. Just like the incident energy distance, the limited and restricted approach boundaries should be on your arc flash labels. Limited approach boundary is not directly tied to the incident energy level but rather to the voltage of the panel upstream, example 600V is a 3ft and 6inch electrical limited approach boundary. Looking to get arc flash labels on your equipment? Contact us for more details. Having a detailed arc flash label on your equipment will spell out exactly what your arc flash boundary working distance is, ensuring you have the proper space to protect from arc flash. Standing outside of the arc flash protection boundary will ensure that you are not exposed. So, does the incident energy have a direct effect on the arc flash boundary distance? Yes! As mentioned above, arc flash distances are increased when dealing with higher incident energy value due to the increased risk of receiving 2nd-degree burns if exposed to an arc flash. So, instead of changing how far away this distance really is the term protection was dropped and now we have the arc flash boundary. The reason this was selected is because that is what is considered the survivable level… not the most comfortable level. This boundary (or invisible barrier) is the distance away from a potential arc flash hazard that someone would receive 2nd-degree burns if exposed to an arc flash. Originally this was referred to as the arc flash protection boundary… until someone realized it didn’t offer much protection. FREE DOWNLOAD: DEFINITIVE GUIDE TO AF STUDIES

Exceeds minimum arc flash boundary