An IG only means it is not connected to the building steel or any other grounding path other than the bus where the main bonding jumper resides. In computer rooms we would pass an insulated green wire unconnected through all the sub panels and attach it in the service disconnect enclosure ground/neutral bus.
A romex wired, dedicated circuit in a plastic box originating in the "main" panel with the service dosconnect IS an IG, even without that expensive orange receptacle and 4 wire circuit (hot, neutral, box ground and IG).
IBM gave up IGs in their specs in the 80s because they figured out it was usually a waste of money. Some data center managers (and "computer science engineers") still insist on it but they are just wasting their money.
