To which of the following is an isolated/insulated equipment grounding conductor prohibited from being connected?

An isolated or insulated equipment grounding conductor is prohibited from being connected to a ground rod that is isolated from the building grounding electrode system because it can create a potentially hazardous situation. The purpose of an equipment grounding conductor is to ensure that electrical faults are safely directed to a low-resistance path back to the grounding system, which ideally is the main grounding electrode system for the building.

When an insulated grounding conductor is connected to a ground rod that is not bonded to the building's grounding system, it may not effectively clear a fault condition. This could lead to differences in potential between the isolated ground and the other portions of the electrical system, posing a risk of electric shock or fire due to inadequate ground fault protection.

In contrast, connecting an insulated grounding conductor to a ground rod that is part of the building's grounding system or other specified connections serves the intended function of grounding and bonding to ensure safety. This is because those connections maintain a common reference point that is essential for proper fault current return paths, helping to safeguard both people and property.