You've raised a very valid and common concern about relying on locknuts and conduit connectors for effective ground fault current paths (GFCP) when dealing with painted enclosures. Here's a breakdown of the issues and why your concern is justified

The Problem: Paint is an Insulator
The Core Issue

Paint, powder coating, and other applied coatings on enclosures are generally insulators. They prevent good electrical contact between the locknut/connector and the metal of the enclosure.

Incidental Contact

As you pointed out, the electrical path primarily relies on incidental contact between the threads of the connector inside the knockout and the (hopefully) unpainted metal of the enclosure. The locknut itself is likely making minimal to no direct contact with bare metal due to the paint.

GFCP Concerns

This incidental contact presents several problems for creating a reliable GFCP:

Variable Resistance

The contact area is small and inconsistent. This results in variable resistance, which can impede fault current flow. A higher resistance means less current flows, potentially delaying or preventing the overcurrent device from tripping in a ground fault situation.

Corrosion

The small contact points are susceptible to corrosion over time, which further increases resistance and weakens the connection.

Mechanical Looseness

Vibration or physical movement can further compromise the already tenuous contact.

Limited Surface Area

The lack of adequate surface area for current flow can lead to arcing and burning at the contact point during a fault, further degrading the connection and potentially causing a fire hazard.

Why the Code Seems Okay With It (and When it Might Not Be)

The NEC does generally allow the use of listed locknuts and connectors for bonding metallic raceway to enclosures. However, this comes with some implicit assumptions and situations where it's not sufficient: Listing/Testing

Listed connectors are tested to specific standards (e.g., UL 514B for conduit fittings). These standards consider the connector's ability to provide a low-impedance fault current path. However, these tests are typically performed with clean, unpainted surfaces. The presence of paint fundamentally changes the situation.



Assumed Good Contact

The NEC assumes that a properly installed locknut and connector will create sufficient electrical contact. This assumption is increasingly challenged by modern enclosures with thicker, more durable coatings.

Specific Requirements for Grounding/Bonding

The NEC has many specific requirements for grounding and bonding, and the general allowance of locknuts for bonding must be seen in the light of these other requirements.

Fault Current Magnitude

For higher fault current situations (e.g., large services, close proximity to the service entrance), relying solely on locknuts for bonding is often inadequate.

Solutions for Ensuring a Proper GFCP on Painted EnclosuresHere's how to ensure a reliable GFCP when dealing with painted or coated enclosures:1.

Remove Paint/Coating at the Connection Point

This is the best and most reliable approach. Use a wire brush, abrasive pad, or paint scraper to remove the coating around the knockout, both inside and outside the enclosure. Expose bare metal before installing the connector and locknut. Apply an anti-oxidant joint compound.2.

Use Grounding Bushings/Connectors

These are designed to bite through the paint and make a positive connection to the enclosure. They typically have a set screw or teeth that penetrate the coating. These are usually required on services.3.

Use Bonding Jumpers

A bonding jumper is a wire (sized according to the NEC) that connects the raceway or equipment directly to the enclosure's grounding busbar or grounding electrode conductor. This bypasses the reliance on the locknut connection and provides a dedicated, low-impedance path. This is not the same as using a ground wire inside the raceway.4.

Tighten Properly

Use the correct tools and torque specifications to ensure the locknut and connector are properly tightened. Over-tightening can damage the connector or enclosure, but under-tightening is a common problem.5.

Consider the Environment

In corrosive or damp environments, even well-made connections can degrade over time. Use corrosion-resistant connectors and consider applying a protective coating after the connection is made.6.

Inspect and Maintain

Regularly inspect bonding connections, especially in critical applications. Look for signs of corrosion, looseness, or damage.

In SummaryYou are absolutely right to question the reliance on locknuts and connectors alone for GFCP in painted enclosures. While the code allows* it in many cases, it's important to recognize the limitations and implement strategies (like those outlined above) to ensure a reliable and safe electrical system. Don't rely solely on incidental contact; take steps to create a positive, low-impedance ground fault current path.Mike Holt's video likely provides general guidance, but it's crucial to apply that guidance with a practical understanding of the real-world conditions and the potential for compromised connections. When in doubt, always err on the side of creating a more robust bonding connection. Consult your local electrical inspector if you have questions about specific situations. Flag for review