Many companies mandate that this is the closest that persons can get to switchgear without the need to wear arc rated specific personal protective gear, whilst others will mandate this is the minimum distance whilst operating that switchgear, or whilst approaching that switchgear with doors open, or covers removed. At this limit the incident energy reduces to, or below 1.2 Cal/cm 2, the threshold of where survivable second-degree burns occurs.

The arc flash boundary is the minimum distance between an energised part and persons, without further protection measures such as barriers and enclosures, to protect against the thermal effects should an arc flash occur. The nominal voltage is the phase to phase (line to line) voltage that should be expected at that point of supply. The working distance is the minimum distance that should be maintained between accessible live parts and persons, their tools and other materials. It should also be noted that if the supply of electricity has been removed from that equipment, the arc flash risk is removed.

It is worth noting that equipment that is well maintained and in good condition should be capable of being operated in its normal way. It is important in that any personal protective equipment worn by operators of the equipment should be able to protect against the incident energy level that is present. This is the calculated energy that would be released on that equipment should an arc fault occur. Incident energy value, which could be stated in a number of units, is often quoted as Calories per centimetre squared. It also contains details relating to protective equipment to be worn when working on or near that equipment whilst it is live. It details the incident energy at the panel and the working distance, the arc flash boundary and the nominal voltage of that equipment. Note: the above distances may be different to those stated in company operational safety rules, DNO standards or transmission standards.Ĭonsider the arc flash warning label above which contains important information. Restricted Approach Boundary Includes Inadvertent Movement Adder Nominal System Voltage Range, Phase to Phase

The table below has been adapted from NFPA 70E, Table 130.4(E)(a) Shock Protection Approach Boundaries to Exposed Energised Electrical Conductors or Circuit Parts for Alternating Current Systems. In Europe we would know this person as an electrically skilled or instructed person, in other words a competent person, again stating the minimum distance that should be maintained from exposed live parts in order to prevent electric shock. Restricted Approach Boundary- approach by a Qualified Person. Typically, in the UK, switchpanels contain live parts within enclosure and it is only when such enclosures are open and live parts are accessible does an issue exist. In Europe we would know this as an ordinary person, that being a person who is neither electrically skilled nor instructed and is the minimum distance that a non-competent person can approach parts that are energized and dangerous. Limited Approach Boundary- approach by Unqualified Persons. This article looks at the arc flash boundary, however, before moving on it is work discussing the limited and restricted approach boundaries that in fact relate to electric shock protection, rather than arc flash control. Dependant on the remit of any arc flash study carried out, labels fitted to switchgear may make reference to one, or all of the above boundaries. Arc Flash Boundary DistancesĪccording to NFPA 70E, three boundaries exist, these are Limited Approach Boundary, Restricted Approach Boundary and Arc Flash Boundary. Compliance Director, Andy Linley, discusses Arc Flash Boundary distances, what they are and factors affecting them.

Arc flash boundary burn level