Q: I read what was written about an air gap for worker protection in the June-July 2020 issue of Incident Prevention magazine, but one of our engineers who sits on a National Electrical Safety Code advisory committee brought something to my attention. NESC C2-2017 444.2 states, “Air gaps created (e.g., cut or open jumpers) for de-energizing equipment or lines for the purpose of protecting employees shall be tagged and meet minimum clearances as specified in Table 444-1 or separated by a properly rated insulator.” What are your thoughts on this matter?
A: Thanks for your question. Our thought is that your colleague is right regarding the table and we missed it.
To remind iP’s readers, in the June-July 2020 Q&A, we addressed what constitutes an air gap and stated that some utilities build their gap rules around minimum approach distance. We pointed out that MAD is a combination of minimum air insulation distance (MAID) and unexpected movement, which is 24 inches for distribution. We gave the example of a dropout switch that has an 8- or 10-inch-plus gap being acceptable where the MAID in a 15-kV distribution exposure is fewer than 2 inches for phase to ground. We could have worded it better, so we hope we didn’t give anyone the idea that MAID is all that’s necessary. In any case, we don’t want anyone to be misled by what we publish.