If you turn to Section 250.122 in your NEC, you find information that has assisted electricians sizing equipment grounding conductors (EGC) for longer than most electricians have even been twisting wire.If you were on the job in 1968, you would have turned to Table 250.95 in your NEC for this information instead of Table 250.122, but the information was essentially the same.In 1968 you also would have found that an ungrounded (hot) branch circuit conductor protected by a 6000-amp overcurrent device required no less than a 1200 kcmil aluminum equipment grounding conductor… assuming you were using an aluminum equipment grounding conductor. That information remained unchanged for 50 years. But as the saying goes, “All good things must come to an end.”
In this 2020 Code cycle a new Informational Note now accompanies the term Grounded Conductor where it is defined in Article 100. The Note has been added to help electricians identify functional differences between Grounded and Grounding Conductors.
In defense of all who have struggled with these terms in the past, both grounded conductors and grounding conductors are in fact grounded. They just have different jobs.
The Isolated Ground (IG) is a type of equipment ground that, in theory, reduces interference experienced by electronics and instrumentation from radio frequency (RF) noise, by connecting that equipment directly to the grounding terminal of the service equipment, without ever making contact with another metal component or grounded surface, that could potentially be serving as an antenna for airborne RF noise.