ARC FLASH BOUNDARY SAFE DISTANCE BASIC INFORMATION AND TUTORIALS

Arc-flash boundaries need to be established around electrical equipment such as switchboards, panelboards, industrial control panels, motor control centers, and similar equipment if you plan to work on or in the proximity of exposed energized components.

Parts are considered exposed if they are energized and not enclosed, shielded, covered, or otherwise protected from contact. Work on these parts includes activities such as examinations, adjustment, servicing, maintenance, or troubleshooting.

Equipment energized below 240 V does not require arc-flash boundary calculation unless it is powered by a 112.5 KVA transformer or larger.

The arc-flash boundary is the limit at which a person working on energized parts can be standing at the time of an arc-flash without risking permanent injury unless they are wearing flame-resistant clothing. Permanent injury results from an arc-flash that causes an incident energy of 1.2 calories/centimeter2 (cal/cm2) or greater and causes a minimum of second-degree burns.

This distance can only be effectively determined by calculating the destructive potential of an arc.

First you must determine the magnitude of the arc based on the available short circuit current, then estimate how long the arc will last based on the interrupting time of the fuse or circuit breaker.

Finally, you will need to calculate how far away an individual must be to avoid being exposed to an incident energy of 1.2 cal/cm2. It may sound like a lot of math and factoring in of potentials, but believe me the extra time you take to determine the arc flash boundary is well worth your safety and well-being.

Calculating flash protection boundaries for systems over 600 V requires performing a flash hazard analysis coupled with either the NFPA 70E Hazard Risk Category/PPE tables or the Incident Energy Formula.

Additionally, Section 4 of IEEE 1584 Guide for Arc Flash Hazard Calculations states that the results of the arc flash hazard analysis are used to identify the flash-protection boundary and the incident energy at assigned working distances throughout any position or level in the overall electrical system.

The purpose is to establish safe work distances and the PPE required to protect workers from injury. A flash-hazard analysis is comprised of the following three different electrical system studies:

1. A short circuit study
2. A protective device time-current coordination study
3. The flash-hazard analysis and application of the data