DC arc flash calculator notes

We strongly recommend that you read the notes below before proceeding with calculations.

General Notes

Note 1: This information is not to be used as a recommendation to work on energized equipment. This information is to help assist in determining the proper PPE to help safeguard a worker from the burns that can be sustained from an arc flash incident. This information does not take into account the effects of pressure, shrapnel, molten metal spray, or the toxic copper vapor resulting from an arc fault. Workers must also be protected against these hazards and therefore additional investigations and additional personal protective equipment may be required.

Note 2: PPE should be utilized any time that work is to be performed on or near energized electrical equipment or equipment that could become energized. Voltage testing while completing the lockout/tagout procedure (putting the equipment in a safe work condition) is considered as working on energized parts per OSHA 1910.333(b). As a general work practice, for the lowest Hazard/Risk Categories (0 & 1), it is suggested utilizing a minimum of voltage rated gloves with leathers, long sleeve cotton shirt, pants, a face shield, safety glasses and hard hat, in addition to the recommendations from NFPA 70E (even though NFPA 70E requirements do not require all these items for the lower Hazard/Risk Categories).

Note 3: To use these methods the available short circuit currents must be calculated at each point in the system that is to be analyzed. In some cases, using conservatively high short circuit currents may result in lower incident energy than what is possible. This is dependent upon the time-current characteristics of the overcurrent protective devices. Calculations should be conducted with both the maximum and minimum available short-circuit current.

Note 4: This information is not intended to promote workers working on or near exposed energized parts. The intent is for those situations such as taking voltage measurement during the lockout/tagout procedures where arc flash analysis must be performed and the worker must utilize adequate PPE.

Note 5: Incident Energy Exposure in this calculator has been set to display a minimum value of 0.25 cal/cm² and a maximum value of 100 cal/cm² (with appropriate warnings). Actual incident energy values may be less than 0.25 but since it is not the intent of this calculator to encourage workers to go without PPE, the .25 cal/cm² default is utilized whenever lower values are encountered. See Note 1 and Note 2. The maximum value of 100 cal/cm² was set because at the time the calculator was created, no PPE is available with an ATPV greater than 100 cal/cm². See Note 1.

Note 6: The parameters for this calculator are based upon an incident energy exposure of 1.2 cal/cm² at an 18in. working distance, 500VDC or less system, short circuit current in the range of 1kA - 50kA, arcs in open air with copper electrodes. Actual results from real arc-flash incidents could be different for a number of reasons, including different system voltage, circuit time constant, distance from the arc, arc gap, electrode material, fuse manufacturer, fuse type, orientation of the worker, grounding scheme etc.

Personal Protective Equipment (PPE) Notes

Employees must wear and be trained in the use of appropriate protective equipment for the possible electrical hazards with which they may face. Examples of equipment could include a hard hat, face shield, flame resistant neck protection, ear protectors, NOMEX suit, insulated rubber gloves with leather protectors, and insulated leather footwear. All protective equipment must meet the requirements as shown in the latest edition of NFPA 70E. Protective equipment, sufficient for protection against the potential electrical flash, is required for every part of the body. The selection of the required thermal rated PPE depends on the incident energy level at the point of work.

As stated previously, the common distance used for most of the low voltage incident energy measurement research and testing is at 18 inches from the arcing fault source. So what energy does a body part experience that is closer to the arc fault than 18 inches? The closer to the arcing fault, the higher the incident energy and blast hazard. This means that when the flash protection analysis results are calculated at 18 inches from the arc fault source, the incident energy and blast energy at the point of the arc fault are considerably greater. Said in another way, even if the body has sufficient PPE for an 18in. working distance, severe injury can result for any part of the body closer than 18in. to the source of the arc.

Disclaimer

This software program, calculations, and other information are intended to clearly present technical information that will help the user determine the thermal arc flash hazard. We reserve the right, without notice, to change this program and to discontinue or limit it's distribution. We also reserve the right to change or update, without notice, any technical information contained on this web site. The data and information presented in this site and/or calculator are believed to be accurate. However, any and all liability for the content, or any omissions from this site, including any inaccuracies, errors, or misstatements in such data, calculations or information, is expressly disclaimed. The software, calculation results and other information are provided without warranty of any kind, either express or implied, but not limited to, the implied warranties of merchantability, or fitness for a particular purpose. We disclaim any liability for the use of this software, calculations or other information.

Agreement

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