The arc flash duration is normally determined from the protective device's time-current curves (TCC's). This approach assumes the device has been maintained and will operate according to the TCC. Most people realize this might be optimistic at best and therefore arc flash studies are usually accompanied by at least one of the following:

>A legal disclaimer stating that it is assumed the protective devices have been properly maintained and will operate according to their published TCC.

>Testing the protective devices and taking necessary corrective action

Here is this week's question:

Which of the following are included in the study to account for poor device maintenance?

(1) Legal disclaimer
(2) Device Testing and Maintenance
(3) None of the Above/Something Else

Select all that apply

I did the study myself, and I'm also responsible for making sure maintenance gets done on the relevant equipment, so there aren't any disclaimers.

Here is a question for a philosophical debate:

If a study has a disclaimer about the data, the condition of the equipment etc. and the utility usually has a disclaimer about their data being based on specific conditions that may change etc. then how much faith do we put into the results of an arc flash study?

It seems that many interpret a study as being an exact science when a) the calculations are approximate from what I understand and b) everything seems to have a disclaimer implying it might not be correct or could change.

This does not provide a comforting feeling when you view it this way.

Not sure about others, but when I perform a study I consider a range of scenarios, to see how the incident energy values fluctuate, and generally use the highest values as the results of the study.

even if everything works according to textbook, NFPA70E includes disclaimers that using the recommended methods will not eliminate injury. I quote those same disclaimers.

There are many variables that are not accurately known when calculating the incident energy in an Arc Flash study and that is why we run multiple scenarios. From that we choose the worst case, erring on the side of caution. I think the biggest take aways from a properly executed Arc Flash study is the verification of the oneline, protective devices (fuse sizes, relay settings, etc.), coordination study, and equipment maintenance (operational checks, cleaning, adjustments, etc.). Arc Flash studies should bring an awareness of the system's state and provide information on areas of higher risk from which then can be prioritized to correct.