There are many statements being made in the field that NFPA 70E® has a preference to use the incident energy analysis method over the PPE category method. One of the stated reasons for this has been that it is first in the standard and the first requirement is always the preferred method. None of this is true. Either method can be used if applicable. Something is only a hierarchy if the standard states the list is in a discrete order (think hierarchy of risk controls which are in a specific descending order of effectiveness or that the explicit primary requirement is that an electrically safe work condition be established.)
NFPA 70E permits the use of either the PPE category method or the incident energy analysis method. The standard does not have a preference since each method has its merits and its limitations. Both achieve a level safety for the worker when energized work is justified. Why use one method over the other? Let’s look at some reasons for each. First, both require that the hierarchy of risk controls be used. Both require that you know the available short-circuit current and fault-clearing time. From there the methods diverge.
To use the PPE category method the equipment must be listed on the table. The specific parameters for that piece of equipment cannot be exceeded. The PPE category and the arc-flash boundary are given. A benefit of the table method is that it does not require that an extensive incident energy evaluation be conducted. It is potentially a quick and effective way to properly label equipment. It provides a simple four level system for required PPE within the facility.
There are limitations in the use of the table method. If the equipment is not on the table or if even one parameter is exceeded the method cannot be used. If the working distance will be closer than specified the method cannot be used. A detriment is that if the actual circuit parameters are well below those specified the PPE category remains the same. Although the hierarchy of risk controls may lower the risk to the worker the PPE category remains the same. The table is either GO or NO GO. There is no interpolation.
A benefit of using the incident energy analysis method is that it can be used on any piece of electrical equipment. It allows a finer pinpoint on the incident energy rather than the broad range of the category method. It can be adjusted for a change in current, clearing time or working distance. One detriment is that it is a very detailed process typically requiring the assistance of an outside consultant or the use of a computer program to perform the calculation. Although no specific method of calculation is required by NFPA 70E, the incident energy analysis method requires that you select the most appropriate calculation method for the type of circuit. This method is often a longer process than the table method. Depending on your viewpoint, having the ability to specify individual PPE for each piece of equipment may be a benefit or detriment.
There are other benefits, detriments and shortcomings of both methods. Regardless of the method selected, of the reason for selecting one method over the other, or other issues associated with a particular method, the main concern is protecting the worker. NFPA 70E allows both methods to used equally. Both may be used in the same facility but must not be used on the same piece of equipment. You must decide which one is applicable for your equipment.
Next time: A misuse of the PPE category tables.