Your described method addresses the specific situation of a vapor barrier separating the concrete slab from direct earth contact, while attempting to meet the intent of a UFER ground and AHJ requirements. Here's a breakdown of potential issues, considerations, and alternative solutions

Issues and Concerns:
Effectiveness of the UFER Ground

The primary concern is the effectiveness of this modified UFER ground. A true UFER relies on the large surface area of concrete in direct contact with the earth to provide a low-impedance path to ground. Your method essentially creates a localized ground point using the exposed copper conductor. While it provides some grounding benefit, its effectiveness compared to a traditional UFER is significantly reduced. The earth contact is limited to the bare conductor, not the entire slab. The resistance to ground will likely be much higher than a true UFER.

Code Compliance (NEC 250.52(A)(3))

While you are attempting to comply with the spirit of the UFER requirement, you are explicitly not meeting the letter of the code. NEC 250.52(A)(3) requires "an electrode encased by at least 2 inches of concrete". The Informational Note specifically states that vapor barriers negate "direct contact." Your AHJ may be enforcing a stricter interpretation of the requirement.

Corrosion of the Bare Copper

The bare copper buried below the vapor barrier will be exposed to moisture and soil, potentially leading to corrosion over time. This could degrade its effectiveness as a grounding electrode and eventually require replacement.

Mechanical Protection of the Buried Conductor

The bare conductor below the vapor barrier is vulnerable to damage during construction or settlement of the soil. While it's underground, there's a risk of it being cut or damaged.

Electrolytic Action/Dissimilar Metals

Connecting copper directly to steel rebar can create a galvanic cell, leading to accelerated corrosion of one or both metals, particularly in the presence of moisture. The exact degree of corrosion would depend on soil conditions.

Possible Issues



AHJ Disapproval

Your AHJ might disapprove of the installation if they strictly interpret NEC 250.52(A)(3) and the Informational Note. Open communication with your AHJ is crucial. Obtain written approval for the method or clarification on their requirements.

Increased Ground Resistance

The modified UFER might not provide the low-impedance ground path needed for effective fault current protection, which could impact the performance of overcurrent protective devices.

Long-Term Reliability

Corrosion and potential damage to the buried conductor could compromise the long-term reliability of the grounding system.

Recommendations and Alternatives


Consult with the AHJ

This is the most important step. Explain your method and the challenges presented by the vapor barrier. Get written approval before installation.2.

Consider Alternative Grounding Electrodes

If the AHJ rejects your method, explore other grounding electrode options listed in NEC 250.52:

Ground Rods (250.52(A)(5))

Drive two ground rods at least 8 feet deep and 6 feet apart. This is a common alternative when a UFER is not feasible. Consider using a corrosion-resistant material for the ground rods (e.g., copper-clad steel).

Grounding Ring (250.52(A)(4))

A bare copper conductor, at least 20 feet long, buried directly in the earth at a depth of at least 30 inches.

Metal Underground Water Pipe (250.52(A)(1))

If available and meets the requirements, this can be used as a grounding electrode.

Other Local Metal Underground Systems or Structures (250.52(A)(2))

Verify with the AHJ if any of these are available and could be used.3.

Improved UFER Ground Connection (If Approved by AHJ)

If the AHJ does approve your method, consider these improvements:

Increase Conductor Length & Contact Area

If possible, increase the length of the bare copper conductor in direct contact with the earth. This would increase the surface area and potentially lower the ground resistance. Consider creating a 'grid' or multiple runs of the bare copper.

Improve Rebar Connection

Use exothermic welding (Cadweld) to connect the copper conductor to the rebar. This provides a permanent, low-resistance connection that minimizes corrosion. Alternatively, use listed grounding clamps designed for direct burial and dissimilar metals (copper to steel).

Consider a Grounding Compound

Use a listed grounding compound (e.g., Bentonite) around the buried conductor to improve its contact with the soil and help reduce soil resistivity.

Corrosion Protection

Apply a suitable corrosion-inhibiting compound to the connections between the copper conductor and the rebar, and consider wrapping the joints with a waterproof tape designed for direct burial.

Mechanical Protection

Enclose the bare copper conductor in a PVC conduit or other suitable protective material where it exits the slab and connects to the service ground. This will protect it from physical damage.4.

Documentation and Testing



Document the Installation

Keep a detailed record of the grounding electrode installation, including the location of the buried conductor, the connection methods used, and any soil treatment applied.

Ground Resistance Testing

Conduct a ground resistance test after installation to verify the effectiveness of the grounding electrode. A low resistance is critical for effective fault clearing. Maintain these records.

Important Considerations



Soil Conditions

The effectiveness of any grounding electrode depends on the soil resistivity. Sandy or rocky soil has high resistivity, making it more difficult to achieve a low-resistance ground.*

Local Codes and Amendments

Always check for local amendments to the NEC that may have specific requirements for grounding electrodes.

In summary, while your attempt to address the vapor barrier issue is commendable, it's critical to consult with your AHJ for approval. If your method is rejected, explore alternative grounding electrode options that comply with the NEC and local codes. If your method is approved, consider the improvements mentioned above to enhance its effectiveness and long-term reliability. Flag for review