This week’s question is from another one of our forum members.

130.5(D) Equipment Labeling provides the option below as one of the methods to address the arc flash hazard/PPE on the arc flash label

- Available incident energy and the corresponding working distance

Or

- Arc flash PPE Category in Table 130.7(C)(15)(A)(b) or Table 130.7(C)(15)(B)

Since Table 130.7(C)(15)(B) is the DC PPE Category, do you believe this means that DC equipment MUST have an arc flash label?
Yes
No
Not sure

It is a different table for DC (than AC) PPE categories, as is the calculation different for DC, however; these differences originate due to different current phenomena, and would not seem to indicate a different importance for doing or not doing the labels.

Other paragraphs in 130.7 include reference to both AC and DC tables interchangeably so it seems the appropriate one or the other is to be applied with equal importance.

We also believe that the intent of the current version of NFPA70E is that DC Equipment should be labeled. This is very important where there are high levels of DC Fault current such as electric arc steel furnace, pot lines or large data centers with paralleled battery banks. More utilities are starting to install very large battery banks to be used for peaking purposes. These battery banks could have a significant amount of DC Fault current and arc flask energy.

Many public trams, light rail, electrified buses, and subways are powered by DC systems. Most of the major Arc Flash Computer programs will enable you to calculate the DC Arc Flash. We have found that some of these transit systems can have a significant amount of Arc Flash energy.
We recommend that these DC systems should have Arc Flash labels.