Okay, this is a common scenario on farms and other locations where you have outbuildings served by their own panels. Here's a breakdown of how to properly bond the grounded (neutral) conductor in your situation, referencing relevant NEC sections, and addressing the lack of metallic water pipe

Understanding the Issue:
Separately Derived System

Each of your panels fed from the CT cabinet is effectively a separately derived system. This means the neutral conductor must be bonded to ground at each panel location.

Grounding Electrode System

Since you don't have a metallic water pipe available (which is the preferred grounding electrode), you need to establish a different Grounding Electrode System (GES).

NEC 250.32 addresses Grounding Requirements for Separate Buildings or Structures. NEC 250.30 Addresses Grounding Separately Derived AC systems.The Solution: Acceptable Grounding Electrode Systems (GES) Options (NEC 250.52)

Without a metallic water pipe, your primary options, in order of typical preference are:1. Concrete-Encased Electrode (Ufer Ground)

(NEC 250.52(A)(3)) If you're pouring any new concrete footings or slabs, this is an excellent choice. It involves burying at least 20 feet of bare copper conductor (typically #4 AWG or larger) within the concrete. This is the most effective method if you have the opportunity.2.

Ground Ring

(NEC 250.52(A)(4)) A bare copper conductor (minimum #2 AWG) encircling the building or structure, buried at least 30 inches below grade. It must be at least 20 feet in length.
3.

Ground Rods or Pipes

(NEC 250.52(A)(5)) This is the most common solution when other options aren't available or practical. You'll need to drive at least two ground rods, spaced at least 6 feet apart. Single ground rods are not permitted unless they can be proven to have a resistance to ground of 25 ohms or less, which is difficult to verify reliably. They must be at least 8 feet in length. Galvanized steel or copper-clad steel are common materials.4.

Other Listed Electrodes

There are other listed and labeled electrodes, which may be suitable as well.

Step-by-Step Implementation


Choose Your Grounding Electrode System

Evaluate your site and determine the most practical GES based on the above options. Concrete encased electrodes are generally superior, but ground rods may be the only feasible solution.2.

Install the Grounding Electrode(s)



Concrete-Encased Electrode

Follow the requirements of NEC 250.52(A)(3) for conductor size, length, and concrete encasement.

Ground Ring

Follow the requirements of NEC 250.52(A)(4).

Ground Rods

Drive the rods at least 8 feet deep and space them at least 6 feet apart. Consider soil conditions; wetter soil is better for conductivity. In rocky soil, you may need to angle the rods.3.

Connect to the Panel



Grounding Electrode Conductor (GEC)

Run a Grounding Electrode Conductor (GEC) from your grounding electrode(s) to the neutral bus (grounded conductor) in the panel. This conductor must be sized according to NEC Table 250.66, based on the size of your service entrance conductors (the 350 kcmil conductors feeding your panels). For 350 kcmil copper conductors, Table 250.66 requires a

#2 AWG copper GEC to your ground rods/concrete encased electrode. Bonding Jumper

Ensure the neutral bus is securely bonded to the panel enclosure with a bonding jumper. This jumper is often already installed in Main Breaker panels, but verify its presence and proper connection.4.

Ground Fault Protection

Because you have parallel conductors in each raceway you will need to use an equipment grounding conductor run in the same raceway and sized per 250.122 and table 250.
122.

Important Considerations



NEC 250.4(A)(1)

This section requires that grounded systems be connected to earth in a manner that limits the voltage to ground. This is what your grounding electrode system accomplishes.

Continuity

All connections must be mechanically sound and electrically continuous. Use approved connectors and methods (e.g., exothermic welds, compression connectors) for joining the GEC to the grounding electrode and the neutral bus. Do not rely on set-screw connectors buried underground, as they are prone to corrosion.

Protection

Protect the GEC from physical damage, especially where it exits the panel and enters the ground. Consider using conduit or other suitable protection.

Inspection

Have your work inspected by a qualified electrical inspector. They will verify that your installation meets all applicable code requirements and is safe.

Avoid Using the Earth as the Sole Grounding Path

Never rely solely on the earth for ground fault current return. The earth's impedance is too high to provide adequate protection.

Documentation

Keep records of your grounding system installation, including conductor sizes, electrode types, and locations. This information will be helpful for future maintenance and troubleshooting.

Example Scenario (Using Ground Rods)

1. Drive two 8-foot ground rods, 6 feet apart, near each panel location.
2. Run a #2 AWG bare copper conductor from the ground rods to the neutral bus in each panel.3. Securely connect the #2 AWG conductor to the ground rods using listed clamps suitable for direct burial.
4. Connect the #2 AWG conductor to the neutral bus in the panel using a listed compression connector or other approved method.5. Ensure the neutral bus is properly bonded to the panel enclosure.

Key Takeaways

Proper grounding is essential for electrical safety and to minimize the risk of electric shock and fire. The absence of a metallic water pipe requires you to establish a suitable Grounding Electrode System. Two properly installed ground rods are usually necessary, unless you can prove a very low ground resistance. The Grounding Electrode Conductor (GEC) must be sized according to NEC Table 250.66.* Always consult with a qualified electrician and local electrical codes to ensure compliance.

Disclaimer: I am an AI chatbot and cannot provide definitive electrical advice. This information is for general educational purposes only. Consult with a licensed and qualified electrician in your area for specific recommendations and code compliance. Electrical work can be dangerous, and improper installation can result in serious injury or death. Flag for review