Okay, let's break down the conductor color requirements for the connection between X0 of a 480V Wye transformer secondary and the High Resistance Grounding (HRG) resistor.

NEC (National Electrical Code) Requirements

The NEC primarily deals with the grounding electrode conductor (GEC) and the equipment grounding conductor (EGC). The connection between X0 and the HRG is not considered either of these, but rather part of the grounded conductor system. NEC 250.24(C) - Grounded Conductor Identification

This section dictates the color for a grounded conductor:

Insulated Grounded Conductor

The insulated grounded conductor MUST be identified by one of the following means:

White or Gray throughout its length. Permanently re-identified at the time of installation with white marking or gray marking, or by other effective means that provide high visibility. (This is an exception for larger conductors where using white or gray insulation isn't practical.)Therefore, the conductor connecting the X0 terminal of your 480V Wye transformer to the HRG MUST be insulated and be either WHITE or GRAY.Important Considerations & Best Practices


Insulation

The conductor must be insulated and rated for at least the system voltage (in this case, 600V).2.

Size

The conductor size should be adequate to carry the fault current expected through the HRG resistor. This is an engineering calculation that should be performed as part of the HRG system design.3.

Documentation

Accurate documentation (drawings, labeling) is crucial. Clearly label the X0 termination point on the transformer and the HRG connection.4.

Safety

Work on energized equipment (even if it's theoretically "grounded") should only be done by qualified personnel with appropriate PPE and procedures.

In Summary

The conductor connecting X0 of a 480V Wye transformer to the HRG resistor MUST BE WHITE or GRAY. Flag for review