No, you cannot use the ground wire as a neutral, even if it is sized per NEC Table 250.102(C)(1). This is a dangerous and code-violating practice. Here's why



Safety Hazard

Ground wires are designed to provide a safe path for fault current to trip a breaker or blow a fuse, protecting people from electric shock. A neutral wire carries the normal return current from the load. If you use the ground wire as a neutral, it will carry this current continuously. If the ground wire becomes disconnected, anything grounded to it (equipment enclosures, metal parts, etc.) could become energized, posing a severe shock hazard.

Code Violation

Using the grounding conductor as a neutral conductor is a clear violation of the National Electrical Code (NEC). Several sections prohibit this, including:

NEC 250.6(A)

"Objectionable Current. Objectionable current that will introduce a safety hazard shall not be permitted to flow over the grounding conductor or grounding path."

NEC 250.24(A)(5)

"The grounded conductor shall not be connected to equipment grounding conductors on the load side of the service disconnecting means..."

NEC 300.3(B)

"All conductors of the same circuit… shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, or cable, or be installed as open conductors. The current carrying conductors and the equipment grounding conductor(s) shall be in the same raceway or cable."

NEC 310.15

Requires that all current carrying conductors be run together in the same raceway to minimize inductive heating.

Electromagnetic Interference (EMI)

Running the neutral current on a separate grounding conductor can create significant EMI issues, potentially disrupting sensitive equipment.

Voltage Drop

A long neutral run with a voltage drop can cause equipment to malfunction and create additional heat which can lead to fires.

Solution1. Install a New Neutral Conductor

The correct and safest solution is to install a new, properly sized neutral conductor from the secondary side of the buck-boost transformer to the secondary fused disconnect switch. While costly, this is the only way to ensure compliance with electrical codes and prevent safety hazards.2.

Consider Alternative Solutions if feasible

Depending on the application, there might be ways to mitigate the need for a neutral. This is highly unlikely, but consider what the 480V is feeding.

Regarding your grounding electrode conductor proposal

Your plan to run a new grounding electrode conductor to the counterpoise at the disconnect location is appropriate in addition to the required equipment grounding conductor (which, again, CANNOT be used as a neutral). Here's why:

Grounding Electrode System

A grounding electrode system (e.g., ground rods, counterpoise) is essential to provide a low-impedance path to earth for fault currents.

Equipment Grounding Conductor

The equipment grounding conductor (EGC) connects the non-current-carrying metal parts of electrical equipment to the grounding system. This ensures that any fault current has a path back to the source to trip a breaker or fuse.

Summary Do not use the existing ground wire as a neutral. This is unsafe and a code violation. Install a new, properly sized neutral conductor.* Ensure a proper grounding electrode system and equipment grounding conductor at the disconnect.

Important: Given the significant distance involved and the potential safety implications, consult with a qualified electrical engineer or electrical inspector to ensure that the final installation meets all applicable codes and safety standards. Flag for review