As the distance between a person and exposed energized conductors or circuit parts decreases, the potential for electrical incident increases [C.1]. If you never let people on site, they won’t be exposed. But that’s an impractical extreme. Thus the real question is, “Just how close can they get?” The imaginary line you could draw upon answering that question is called the approach boundary.
But there are three types of approach boundary:
- Arc flash. Only persons who are wearing the appropriate PPE and who are under the close supervision of a qualified person may cross this boundary.
- Limited. The distance from the exposed energized conductors or circuit parts, including the longest conductive object being handled, so people cannot contact or enter a specified air insulation distance to the exposed energized conductors or circuit parts [C.1.1]. Any unqualified person crossing this boundary must be continuously escorted by a qualified person.
- Restricted. This is off-limits to an unqualified person. Special shock protection techniques and equipment are required.
These are visually represented in Figure C.1.2.3.
Annex C provides guidance on crossing all three of these boundaries:
- Arc flash. Determine the boundary and what PPE must be used [C.1.1].
- Limited. To cross this, a person must meet two criteria. Basically, that person needs to be able to identify the risks [C.1.2.2].
- Restricted. To cross this, a person must meet four criteria. One of those is to have an energized electrical work permit authorized by management [C.1.3(1)].
The remainder of Annex C provides the basis for the distance values in Tables 130.4(E)(a) and 130.4(E)(b). While you don’t have to know this information, a good read-through or two will help you understand why those tables have the values they do. That can be useful if you get pushback from, say, operators who try to cross your boundary tape. You can explain to them why the tape is where it is. This understanding can also be useful where compliance among electrical crew members appears to be problematic.
If you want to skip all of the technical stuff, you can just read to them the first half of the last sentence in Annex C: “These values have been found to adequate over years of use….” In other words, there’s real-life experience behind these numbers.
