Okay, this is a common and important question regarding safety around transformers. Here's a breakdown of the requirements and best practices, addressing your specific situation

NEC Requirements and Reasoning
NEC 250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s). This section requires the grounding electrode system to be connected to the grounding electrode conductor, grounding bus, or grounding terminal. NEC 250.104(A) Metal Water Piping. This section requires the grounding of any metal water piping. NEC 250.104(B) Other Metal Piping. This section requires the grounding of other metal piping systems that are likely to become energized. NEC 250.104(C) Structural Metal. This section requires the grounding of structural metal that is likely to become energized. General Principle

The overarching goal of grounding and bonding is to create a low-impedance path for fault current to return to the source, allowing overcurrent protective devices (circuit breakers or fuses) to quickly trip and clear the fault. This minimizes the risk of electrical shock to personnel.

Analysis of Your Situation1. No Direct Earth Contact

The key factor here is that the fence posts are not in direct contact with the earth. They are mounted on the concrete containment area. This significantly reduces the likelihood of the fence becoming energized from ground faults.2.

Transformer as a Separately Derived System (SDS)

Your transformer is acting as an SDS, stepping down the voltage from 13.8 kV to 480 V. As such, it requires its own grounding electrode system. This system is established at the transformer itself.
3.

Potential for Energization

While the fence is not directly grounded, it could become energized in the event of a fault within the transformer. For example, if a high-voltage conductor were to come into contact with the transformer's enclosure and that enclosure were to become electrically connected to the fence (through a faulty connection or arcing).

Is Bonding Necessary? Likely, Yes

While the NEC doesn't have a section that specifically calls out fencing around transformers, the intent of the code, along with best practices for safety, strongly suggests that bonding the fence to the transformer's grounding electrode system is a good idea.

Recommendations and Best Practices1. Bond the Fence

Connect the fence to the transformer's grounding electrode system using a properly sized grounding conductor (based on the size of the transformer's conductors per NEC 250.66). This could be a copper wire (bare or insulated) run from a grounding point on the transformer enclosure to the fence.
2.

Bonding Points

Bond the fence at multiple points, especially at corners and at regular intervals along the fence line. This creates a more effective and redundant path for fault current.3.

Consider the Concrete

While concrete is not a good conductor, it can become conductive when wet or contaminated with salts or minerals. If there's a high likelihood of this, consider additional grounding measures.4.

Signage

Post warning signs on the fence indicating the presence of high voltage and the importance of not touching the fence.5.

Review Local Codes

Check with your local electrical inspector or authority having jurisdiction (AHJ). They may have specific requirements for transformer installations and fencing in your area.

Why Bond Even Though It's Not Directly Grounded? Safety

Bonding the fence provides a low-impedance path for fault current. If the fence becomes energized, this will cause the overcurrent protective device (breaker or fuse) to trip quickly, minimizing the risk of electric shock.

Equal Potential

Bonding helps to ensure that the fence is at the same electrical potential as the transformer enclosure and other grounded metal parts. This reduces the risk of voltage gradients and step potential, which can be dangerous.*

Peace of Mind

Bonding is a relatively inexpensive measure that can significantly improve the safety of your transformer installation.

In Summary

Although your fence is not directly earth-grounded, bonding it to the transformer's grounding electrode system is highly recommended and likely necessary to meet the intent of the NEC and ensure the safety of personnel. Consult with a qualified electrical engineer or your local electrical inspector to determine the best approach for your specific installation. They can assess the risks and provide specific recommendations based on your site conditions. Flag for review