Okay, dealing with a corner-grounded delta system requires careful attention to detail. Here's a breakdown of your questions and considerations

1) Fusing the Grounded Conductor (B Phase)
You are correct

NEC 240.22 generally prohibits overcurrent protection in grounded conductors. It's very likely that fusing the grounded B phase in both the switchgear and the transformer primary disconnects is a violation and should be corrected.

Remedy

As you suggested, replace the fuse with a solid copper link or bus bar in the B phase position in both the switchgear and the transformer primary disconnect.

However, be absolutely certain this is the grounded phase before doing so! Verify with a meter and phase tracer. Motor Disconnect Exception

The exception you mentioned about motor disconnects is not directly relevant in your specific case. You are dealing with a feeder to transformers, not a motor branch circuit.

Important

Before making any changes, verify absolutely that the B phase is, in fact, the grounded phase. Use a voltmeter to check voltage from each phase (A, B, C) to ground. The grounded phase will show 0V to ground. Use a phase rotation meter or tracer to confirm the phase sequence.

2) Transformer Primary Connections (480V Delta) Neutral Point

In a corner-grounded delta system, there isn't a true "neutral" on the primary side in the sense of a wye system. Each phase wire carries the same voltage to ground due to one phase being grounded.

Connection Doesn't Matter (Generally)

In most cases, it technically shouldn't matter which primary terminal (H1, H2, or H3) receives the grounded B phase as long as the transformer is designed for delta connection on the primary side. However, you should

always consult the transformer nameplate or manufacturer's documentation if available. Some older transformers might have specific connection requirements. If there is a need for a control power transformer (CPT), a specific primary phase should be designated for the CPT connection as there would then be an importance as to which phase is connected to which terminal. Best Practice

As a matter of good practice and future troubleshooting, it's generally a good idea to establish a consistent connection scheme. For example, always connect the grounded B phase to H2 (or whichever terminal you choose) for all similar transformers in the facility. Document this clearly.

3) Transformer Grounding You are correct

Your grounding plan is generally correct for a separately derived system.

EGC

Run an equipment grounding conductor (EGC) from the switchgear to the transformer enclosure. This provides a low-impedance path for fault current back to the source.

Secondary Bonding

Bond the X0 (neutral point) of the 120/208V Y secondary to the transformer case.

GEC

Run a grounding electrode conductor (GEC) from the transformer case to the nearest qualifying grounding electrode (e.g., building steel, ground rod, water pipe). Size the GEC according to NEC Table 250.66, based on the size of the ungrounded conductors.

Grounding Electrode System

If multiple grounding electrodes are present, you may need to bond them together to create a comprehensive grounding electrode system, per NEC 250.50.

Separately Derived System

Make sure you properly install the GEC at the same point where the neutral (X0) is bonded to the transformer case.

Grounding Impedance

It's important to ensure that the grounding impedance is low enough to allow for adequate fault current flow.

4) Supervision by an On-Site Electrician Absolutely

This type of work requires supervision by a qualified and experienced electrician on-site. Here's why:

Safety

Working with 480V, especially in an old system, is inherently dangerous.

Code Compliance

Ensuring compliance with the NEC and any local codes is critical.

System Understanding

A qualified electrician will have the necessary knowledge of corner-grounded delta systems and can make informed decisions.

Troubleshooting

Unexpected issues are common in older installations. An experienced electrician can diagnose and resolve problems efficiently.

Liability

You don't want to be liable for any issues caused by improper wiring or grounding.

Additional Considerations



Insulation Testing

Consider performing insulation resistance tests (megger testing) on the existing conductors before and after energizing the system.

Arc Flash Hazard

Assess the arc flash hazard at the switchgear and transformer locations and take appropriate precautions.

Documentation

Document all changes you make, including wire sizes, grounding connections, and transformer connection diagrams.

Overcurrent Protection Coordination

Verify that the overcurrent protective devices are properly coordinated to provide selective tripping and minimize outages.*

Older Equipment

Be aware that older equipment may have different standards and tolerances than modern equipment. Inspect the equipment carefully for signs of damage or deterioration.

In summary, proceed cautiously, verify everything, and involve a qualified electrician. Safety should be your top priority! Flag for review