Approach Distance vs Arc Flash Boundary: Understanding the Difference

When it comes to electrical systems, understanding the approach distance versus arc flash boundary is crucial for ensuring worker safety. In this article, we will delve into the difference between these two concepts and how they impact the calculation of incident energy.

Default Low Voltage Working Distance

The default low voltage working distance in many programs is 18 inches (457.2 mm), which may seem arbitrary at first glance. However, it is actually based on a standard arc flash boundary calculation method that takes into account various factors such as fault current and fuse equations. The IEEE 1584 CL Fuse Equations provide incident energy calculations for distances of 455mm, but this does not necessarily translate to other distances.

Arc Flash Hazard Report

When the Arc Flash Hazard Report is generated, it shows bolted fault current but not arc current or trip times. This is because these values are not used in determining incident energy. The report only provides information on the incident energy and the corresponding approach distance.

IEEE 1584-2018 Standard

The IEEE 1584-2018 standard outlines a specific method for calculating let-through arc flash incident energy based on bolted fault currents and UL class of fuse. This method is applicable to low-voltage systems only and uses equations available for classes L and RK1. The calculations are only valid when the fault current is high compared to the minimum fault current required for current limiting.

Approach Distance

The approach distance refers to the distance between a worker and an electrical source at which the incident energy is less than or equal to 1.2 cal/cm². This boundary is defined by the IEEE 1584-2018 standard and is based on the calculation of let-through arc flash incident energy.

In conclusion, understanding the difference between approach distance and arc flash boundary is critical for ensuring worker safety in electrical systems. By grasping the concepts outlined above, electrical professionals can better calculate incident energy and ensure compliance with relevant standards. Whether working with low-voltage systems or high-voltage systems, a thorough understanding of these concepts is essential for preventing electrical accidents.

References

IEEE 1584 CL Fuse Equations

IEEE 1584-2018 Standard

Arc Flash Hazard Report

Approach distance vs arc flash boundary