Okay, this is a tough situation, but a common one. Let's break it down and explore your options, keeping in mind you need a code-compliant and practical solution.

Understanding the Issue

The AHJ is correct to flag this. The Secondary System Bonding Jumper (SSBJ) is not the same as an Equipment Grounding Conductor (EGC). While an EGC provides a low-impedance path for fault current back to the source (the transformer in this case), the SSBJ connects the grounded conductor (neutral) to the equipment grounding system at the separately derived system (SDS). Its primary purpose is to ensure a low-impedance path for fault current to facilitate the operation of the overcurrent protective devices.

Addressing Your Questions


Pulling an Additional Ground Wire



The Reality

Pulling an additional wire into an already crowded conduit, especially with multiple bends, is risky. The existing conductors' insulation could be damaged, leading to future problems.

Assessment



Evaluate Conduit Fill

Even with 20-28% fill, adding another conductor will increase that substantially. Check if you're still within code limits after the addition.

Consider Lubricant

If you attempt this, use a generous amount of high-quality wire pulling lubricant specifically designed for the insulation type of your conductors.

Careful Technique

Use a pulling rope or fish tape and pull slowly and steadily. Avoid jerking or forcing the wire.

Inspection

After the pull, visually inspect each conductor at both ends for any signs of insulation damage.

Recommendation

While technically possible, pulling an additional conductor is a gamble. The 2-3 month estimate of pulling out the whole feeder is a good starting point for negotiations with the client, but there might be a middle ground - for example, the contractor could allocate more electricians to this task.2.

Using Conduit as SSBJ with Jumper over FMC



The Code

250.30(A)(2) does allow the metal raceway itself to be used as the SSBJ if it meets specific conditions, primarily continuous electrical continuity. FMC does not meet this requirement.

The Jumper

250.30(A)(1) allows you to use a wire-type SSBJ with a raceway.

The Issue

The core issue is that you can't simply "jumper" over the FMC section and declare the EMT portion as the sole SSBJ path. The entire path from the transformer's ground terminal to the panelboard's ground terminal must meet the SSBJ requirements.

NEC Compliance

250.102(C)(1) discusses bonding jumpers on the supply side (which includes SSBJs). There is nothing in this section that would prohibit the use of an external jumper to bridge the FMC gap, provided it is appropriately sized and installed.

Recommendation

This is likely the most practical and code-compliant solution. Use a appropriately sized bonding jumper per 250.102(C)(1), running it externally from the EMT to the panelboard ground. Securely clamp the jumper to the EMT at both ends to ensure a solid connection. The jumper needs to be large enough for the entire fault current rating, so it cannot be one size smaller.3.

Dangers of an Undersized SSBJ



The Core Concern

The primary danger is the inability of the SSBJ to carry the necessary fault current to trip the overcurrent protective device quickly enough.

Specifically



Voltage Rise

An undersized SSBJ will have higher impedance. This can cause a significant voltage rise on the grounding system during a ground fault, potentially damaging equipment connected to that grounding system, and creating touch potential hazards.

Delayed Tripping

Slower tripping of the OCPD increases the duration of the fault current. This generates more heat, which can damage the transformer, conductors, and other equipment. It also significantly increases the risk of electrical fire.

Mechanical Stress

High fault currents create strong magnetic fields. An undersized SSBJ may not be able to withstand the mechanical stress from these fields, leading to its failure.

Fault Location Matters



Fault Between Transformer and Secondary OCPD

You're correct. The SSBJ must handle the fault current until the primary OCPD trips. This is the most critical scenario.

Fault Downstream of Secondary OCPD

The SSBJ still plays a crucial role as part of the EGC path, but the secondary OCPD will likely trip faster than the primary in this scenario. However, remember, the SSBJ still needs to be adequately sized for any fault current it might carry.

Experiences

While it's difficult to directly point to a specific incident solely caused by an undersized SSBJ (because other factors usually contribute), undersized bonding and grounding conductors are frequent culprits in electrical failures and fires. They contribute to a generally less robust and less safe electrical system.

Your Action Plan (Prioritized)


Negotiate with the AHJ

Explain the practicality of the external jumper solution (using appropriately sized bonding jumper from EMT to panelboard ground) as described above. This minimizes disruption and potential damage. Show the AHJ that the external jumper is sized to meet the requirements of 250.102(C)(1).
2.

Cost Analysis

Get a detailed cost breakdown for each option:

Pulling New Wires (with contingencies for damage and delays)

Labor Materials (new conductors, lubricant) Potential for downtime (if the building cannot partially open with this work ongoing)

External Jumper Solution

Labor Materials (bonding jumpers, clamps)

Replacing the Entire Feeder Run

Labor Materials (new conductors, conduit, fittings) Significant downtime3.

Present Options to the Client

Clearly explain the pros, cons, costs, and risks associated with each approach. Emphasize the importance of safety and code compliance. Let the client make the informed decision, understanding the potential consequences of cutting corners.4.

If the Jumper is Approved



Ensure Proper Installation

The clamps must be rated for grounding and bonding, and they must be securely tightened to the EMT.

Document Everything

Take photos of the installation before and after the jumpers are installed. Keep records of conductor sizes, clamp types, and any testing performed to verify the integrity of the bonding path.

Key Considerations



Documentation

Ensure all documentation is updated to reflect the chosen solution, including drawings and specifications.

Testing

Consider performing impedance testing on the completed grounding system to verify the effectiveness of the bonding jumpers.

Communication

Maintain open and transparent communication with the AHJ, contractor, and client throughout the process.

Long-Term Safety: Focus on creating a robust and safe electrical system that will protect the building and its occupants for years to come.This is a challenging situation, but by carefully evaluating your options, communicating effectively, and prioritizing safety, you can find a solution that meets both the client's needs and the code requirements. Good luck! Flag for review