Okay, let's break this down. You're dealing with the grounding of separately derived systems (SDS), which dry-type transformers certainly are. The key to understanding this lies in the purpose and application of the Grounding Electrode Conductor (GEC), the System Bonding Jumper (SBJ), and the Equipment Grounding Conductor (EGC).

Your Situation

You have a separately derived system (SDS) in the form of dry-type transformers. You have a grounding electrode system (GES) consisting of Ufer ground and building steel, connected to a buss bar in the electrical room. You are running a GEC from your buss bar in the electrical room to a ground buss in the transformer (provided by the factory). Your G.F. believes the GEC needs to connect to the X0 terminal of the transformer before connecting to the ground buss in the transformer.

Code References (NEC 2023)



250.20(D): Grounded Systems. Separately derived ac systems that are required to be grounded shall be grounded as specified in Part V of Article 250. 250.30 Grounding Separately Derived AC Systems. This section gives the requirements for grounding separately derived systems. 250.30(A)(1): System Grounding Connection. A system bonding jumper shall connect the grounded conductor of each separately derived ac system to the transformer or other source of the system. This connection shall be made at any single point on the separately derived system from the source to the first system disconnecting means or overcurrent protective device, or it shall be made at the source of the separately derived system. 250.30(A)(2): Grounding Electrode Conductor Connection. The grounding electrode conductor shall be connected to the grounded conductor of the separately derived system as specified in 250.30(A)(1). This connection shall be made at the same point on the separately derived system where the system bonding jumper is connected. 250.30(A)(3): Grounding Electrode Conductor for a Single separately Derived System. The grounding electrode conductor shall be sized in accordance with 250.66, based on the derived phase conductors. The grounding electrode conductor shall be permitted to be run to any convenient grounding electrode available as described in 250.
52. 250.30(A)(6): Metal Enclosure Bonding. Noncurrent-carrying metal enclosures, raceways, and equipment shall be connected to the system grounding electrode conductor or to the grounded conductor of the separately derived system, in accordance with 250.134 and 250.
136.

Analysis


The Key is the System Bonding Jumper (SBJ) and GEC connection Point

NEC 250.30(A)(1) and 250.30(A)(2) are very specific. The system bonding jumper connects the grounded conductor (usually the neutral, X0) to the transformer enclosure or frame, and the grounding electrode conductor connects to that same point. Essentially, the GEC connection point (and SBJ connection) should be as close to the X0 as practical.2.

Factory-Provided Ground Buss

The presence of a factory-provided ground buss changes the situation. If the factory has bonded the X0 terminal to the transformer's enclosure and then provided a ground buss intended as the single point connection for the GEC, then your installation could be compliant.

However, this is highly dependent on the factory instructions and documentation.3. Intent of the Code

The intent of the code is to provide a low-impedance path back to the source for ground fault current. By bonding the neutral (X0) to the enclosure and then running the GEC from the enclosure, you are essentially achieving this goal. However, you need to ensure this path is well-defined and properly sized.4.

Common Misconception? The idea that the GEC must connect directly to the X0 terminal without anything in between is often a misconception. The code requires the GEC to connect to the same point where the SBJ connects the X0 to the transformer.

Here's what you need to verify and consider



Transformer Documentation

Crucially, check the transformer's installation instructions. These instructions should detail how the transformer is intended to be grounded and where the GEC should be connected. If the instructions say to connect the GEC to the factory-provided ground buss, and the X0 is bonded to the enclosure that buss is connected to, then you may be compliant.

Factory Bonding

Verify that the X0 terminal is indeed bonded to the transformer's enclosure. Sometimes this is done internally, and sometimes it's a separate bonding strap that needs to be installed.

Ground Buss Construction

Ensure the factory-provided ground buss is robust and adequately sized to handle the potential ground fault current. It should be securely connected to the transformer's frame.

Inspectors Opinion

Inspectors have the final authority on code interpretations. It's always best to discuss the installation with the inspector before they arrive for the inspection. This gives you a chance to explain your reasoning, show them the transformer documentation, and address any concerns they may have.

System Bonding Jumper (SBJ) Sizing

Size the System Bonding Jumper per NEC 250.28.

GEC Sizing

Size the Grounding Electrode Conductor per NEC 250.66, based on the size of the derived phase conductors.*

EGC (Equipment Grounding Conductor) Sizing

Size the Equipment Grounding Conductor per NEC 250.122, based on the size of the overcurrent protective device.

Recommendations


Consult the Transformer Manufacturer's Documentation

This is the most important step. See what the manufacturer intended.2.

Discuss with the Inspector

Before making any changes, talk to the inspector. Explain your approach and show them the transformer documentation. They may be okay with your current installation if it meets the intent of the code and the manufacturer's instructions.3.

If in doubt, modify the installation

If there is any doubt in the inspector's mind (or yours) that the current installation is compliant, the safest option is to modify the installation to more closely align with a direct connection to the X0. This might involve moving the GEC connection closer to the X0 terminal.
4.

Document everything

Keep a record of all your conversations with the inspector, any documentation you have from the manufacturer, and any changes you make to the installation.

In summary, you are likely meeting the intent of the code, BUT ONLY IF the factory designed the transformer that way. It's critical to consult the documentation and discuss the installation with the inspector. Flag for review