Okay, let's break down the grounding requirements for this situation based on the NEC (National Electrical Code).

The Core Issues



LFMC (Liquidtight Flexible Metal Conduit)

LFMC, by itself, cannot be relied upon as the primary equipment grounding conductor (EGC) for circuits over 250 volts.

Bonding Requirements

Proper bonding ensures a low-impedance fault current path back to the source (transformer) to facilitate the operation of overcurrent protective devices (circuit breakers or fuses) in case of a ground fault.

Service vs. Feeder

While you mention it's not service equipment, the principle of effective grounding remains critical.

Fault Current Path

The conduit is the EGC, so the connection to the panel must be secure.

Analysis Based on NEC and Good Practice


Inadequate Grounding with Current Setup

Your description indicates the current LFMC setup is NOT adequately grounded according to NEC. Here's why:

LFMC Alone Not Sufficient

As stated above, LFMC cannot be used as the sole EGC for circuits above 250 volts, like your 208V circuit (NEC 350.60). However, there are exceptions when listed fittings are used and the grounding conductor is installed inside of the LFMC.



Missing External Locknut

The absence of a locknut on the outside of the panelboard enclosure is a problem. This means the conduit fitting isn't making a mechanically secure and electrically conductive connection to the enclosure. A locknut should be tightened against the outside of the enclosure to ensure good contact.

Single Internal Locknut Insufficient

A single locknut inside the enclosure alone is not enough. It's more about securing the fitting than providing a reliable grounding path.

Plastic Bushing

A plastic bushing does not provide any grounding or bonding. It's for protection of the conductors, not for electrical conductivity.2.

Required Corrective Action

You need to provide a proper equipment grounding conductor (EGC) in addition to the LFMC. Here are your options, listed in order of preference/common practice:

Grounding Conductor Inside LFMC

The best and most common approach is to pull a properly sized insulated equipment grounding conductor (EGC) inside the LFMC along with the circuit conductors (phase conductors and neutral). The EGC must be sized according to NEC Table 250.122, based on the rating of the overcurrent protection device protecting the circuit. This is the most reliable and preferred method. This EGC would then be connected to the ground bar in the panelboard and to the grounding point in the transformer enclosure. The LFMC could still be considered an additional path, but the code requires the proper EGC in the conduit.

Grounding/Bonding Bushing and Jumper

The bare minimum that you could do (though the above is highly recommended) is to install a grounding bushing (a metallic bushing with a lug for a ground wire) inside the panelboard. You would then connect a bonding jumper from this grounding bushing to the panelboard's grounding busbar. This jumper must be sized according to NEC Table 250.102(C)(1) based on the derived ungrounded conductors (phase wires). The fitting you use must be listed for grounding and bonding.

Important Considerations for Grounding Bushing

If you use this method, make sure: The grounding bushing is UL-listed for grounding purposes. The bonding jumper is sized correctly (use the NEC table mentioned above). The surfaces where the grounding bushing contacts the panelboard enclosure are clean and free of paint or corrosion. Ensure the locknut is tightened securely against the outside of the enclosure. This method is not the ideal solution, as it relies on the LFMC's connections for grounding, which are inherently less reliable than a dedicated EGC.3.

Why is a Dedicated EGC in the LFMC Preferred?

Redundancy

Provides a dedicated, low-impedance path for fault current.

Reliability

Less reliant on the mechanical connections of the LFMC.

Code Compliance

Directly addresses the NEC requirements for EGCs.

Specific Recommendations for Your Situation


Install an insulated EGC

Pull a properly sized insulated EGC inside the existing LFMC. Terminate it on the ground bar of the panelboard and back at the transformer's grounding point. This is the recommended solution.2.

Add the missing locknut

Even if you install an EGC inside the conduit, install a locknut on the outside of the enclosure to properly secure the conduit.3.

Consider a grounding bushing (less preferred)

If running a new EGC inside the conduit is impossible, use a grounding bushing inside the panelboard with a correctly sized bonding jumper to the ground bus.

Important Notes



Local AHJ (Authority Having Jurisdiction)

Always consult with your local electrical inspector (AHJ) for specific interpretations and requirements in your area. They have the final say on what is acceptable.

NEC Edition

Make sure you are using the correct edition of the NEC that is enforced in your jurisdiction. Code requirements can change between editions.

Qualified Electrician: This type of work should only be performed by a qualified and licensed electrician.By following these guidelines, you can ensure that your 208V three-phase circuit is properly grounded and bonded, providing a safe and reliable electrical system. Remember that electrical safety is paramount, and compliance with the NEC is essential. Flag for review