Last edit: 17/04/2023
IEEE 1584 is a guide that aims to provide models and analytic processes for calculating the caracteristics of an electric arc flash.
It is essential to know these characteristics because, depending on these, the necessary PPE and the measures to be taken to ensure the safety of electrical maintenance personnel during live work are chosen.
It is emphasized that the guide deals with electric arcs in alternating current systems, with operating voltage between 208 V and 15.000 V. Single-phase electric arcs or direct current electric arcs are not covered by the guide, even if the latter still provides guidelines in this regard.
The current versione of the IEEE 1584 guide was pulished in 2018 and replaces the 2002 version. During that time, the analytic model was perfected as, in the meantime, hundreds of experimental tests were carried out in special laboratories and in fact, the differences with the previous version are quite remarkable; it can be said that the guide as been completely revisited.
The normal process defined by the guide for calculating the characteristics of an electric arc basically consists of the following steps:
- Field collection of data and considerations regarding the type of electrical distribution. This is probably the most important part of the process; this implies for example:
- define the characteristics of the electrical distribution. For this reason it is very useful to have a single-line diagram of the electrical distribution that is being analyzed.
define the operating modes of the system (for example, if there are users that receive multiple power supplies at the same time)
calculate and / or measure the short-circuit current values directly in the fiel
detect the model and characteristics of the switches
Definition of calculation parameters. The main parameters to know in order to carry out an Arc Flash analysis are the following:
- Short-circuit current
Physical space between conductors where the electric arc occurs
Electrode configuration (for example, their orientation)
Typical working distance, established by law according to the operating voltage of the equipment
Calculation of the characteristics of the Arc Flash. The essential parameters to be calculated are:
- The arcing current, which mainly depends on the short-circuit current
The duration of the arc, which is influenced by the time taken by the circuit breaker to extinguish the arc.
The energy of the arc
The Arc Flash Boundary or the distance between the point of origin of the Arc Flash and the point where the energy of the arc is equivalent to 1.2 cal / cm2.
With the exception of the arc duration, which can be obtained by consulting the circuit-breaker datasheets, it is possible to calculate the parameters just listed using the formulas and coefficients provided directly by the guide.
Now that we know the characteristics of the Arc Flash, it is necessary to manage the risk. This can be done:
- By reporting the characteristics of the electric arc on each single piece of equipment. Usually this is done by means of the "Arc Flash Hazard Labels", or signs showing the characteristics of the electrical equipment and of the arc.
By wearing appropriate PPE (Personal Protective Equipment)
However, the guide DOES NOT provide any information regarding the Arc Flash Hazard Labels, nor regarding the type of PPE to wear.
These aspects are dealt with by the NFPA 70E standard, which defines the characteristics that an Arc Flash Label must have and the required PPE according to the Arc Energy.
The NFPA 70E standard defines Energy ranges and for each of them indicates the PPE that is mandatory to wear. For example, if it was necessary to carry out live work on equipment with an arc energy equal to 10 cal / cm2, it would be mandatory to wear:
- Arc-rated long-sleeve shirt and pants or arc-rated coverall
- Arc-rated flash suit hood or arc-rated face shield and arc-rated balaclava
- Arc-rated jacket, parka, rainwear, or hard hat liner (AN)
- Hard hat
- Safety glasses or safety goggles (SR)
- Hearing protection (ear canal inserts)
- Heavy-duty leather gloves
- Leather footwear
In extreme cases, the PPE to wear could be the ones represented in this image.
GT Engineering carries out the Arc Flash Risk Analysis according to the IEEE 1584 guide and also provides the Arc Flash Hazard Labels with the values required by NFPA 70E standard.