Okay, let's break down this scenario and the grounding requirements, focusing on the intent of the code and best practices for safety and compliance.

Understanding the Setup Service Entrance

Meter > EM Disconnect (outside) > Panel (inside, basement). The panel is the service equipment.

Verizon FiOS ONT

Located next to the panel inside.

Indoor IBT

Installed above the panel, connected to the ONT.

Goal

Ground an outdoor TV antenna, and the code requires connection to an Interconnecting Bonding Terminal (IBT).

NEC Requirements and Analysis NEC 810.21(F)(1) and (2)

These sections do require the antenna grounding conductor to be bonded to the building's grounding electrode system via an IBT. The IBT serves as a central point for bonding communication systems (like the ONT and antenna) to the grounding electrode system, minimizing potential differences and reducing surge damage. 810.21(F)(1) does say that "A listed Interconnecting Bonding Terminal (IBT) shall be permitted for connecting intersystem bonding conductors to the building grounding electrode system" and section (2) speaks of the required characteristics of the bonding jumper.

The Issue

You're concerned about running the antenna grounding conductor all the way inside to the existing IBT near the panel. It seems illogical to penetrate the building solely for grounding, and you're right, it's often not ideal, especially in terms of potential for water intrusion, etc.

The Crux: IBT Placement and Intent The intent of the IBT is to provide a convenient and accessible point for bonding communication systems to the grounding electrode system. It is not explicitly stated where they must be located, or how many must be installed.

Is an Additional Outdoor IBT Required?Yes, it is the best practice, and arguably NEC compliant to install an additional IBT outdoors.

Here's why:1. Convenience and Shorter Grounding Path

It makes far more sense to install a second IBT outside, as close as possible to the EM disconnect and the point where the antenna grounding conductor enters the building. This keeps the antenna grounding conductor run short and direct, minimizing impedance and improving grounding effectiveness.2.

Reduced Penetrations

It avoids unnecessary penetration of the building wall.3.

Better Surge Protection

A shorter antenna grounding conductor is more effective at shunting surge energy to ground.4.

Compliance with Intent

While you already have an IBT inside, the outdoor IBT would better serve the purpose of bonding communication systems entering the building from the outside. It's more in line with the spirit of the code, even if not explicitly mandated.5.

Clarity and Future Expansion

An outdoor IBT provides a clear, designated point for grounding other outdoor communication equipment that might be installed later (e.g., satellite dishes, network cables to outbuildings, etc.).

How to Implement


Install the Outdoor IBT

Mount a listed IBT near the EM disconnect, in a weatherproof enclosure.2.

Bond to the Grounding Electrode System

Connect the outdoor IBT to the nearest available grounding electrode conductor (GEC), grounding electrode, or bonding jumper connected to the grounding electrode system. This is critical! This can be the grounding electrode conductor going to the grounding rod, or the metal water pipe (if used as a grounding electrode), or a building steel member used as a grounding electrode. Use the shortest, straightest path possible. #6 AWG copper minimum, larger if required by the service size.3.

Bond Between IBTs (Optional, but Recommended)

Run a bonding jumper between the outdoor IBT and the indoor IBT. This creates an equipotential bond and helps to equalize voltage potentials between the two locations. Again, #6 AWG copper minimum, larger if required by the service size.4.

Connect Antenna Grounding Conductor

Connect the antenna grounding conductor to the outdoor IBT.5.

Connect ONT Grounding Conductor

Connect the ONT grounding conductor to the indoor IBT.

Important Considerations



Listed IBT

Use only a listed IBT. This ensures it meets safety standards.

Proper Connections

Use appropriate connectors for the conductors and the IBT. Make sure all connections are tight and corrosion-resistant.

Accessibility

Ensure the IBT is accessible for inspection and maintenance.

Local Amendments

Always check with your local AHJ (Authority Having Jurisdiction) for any specific amendments to the NEC that might apply in your area. They have the final say.

In summary: While technically you could* run the antenna grounding conductor all the way inside, installing an additional IBT outside is the better, safer, and more practical solution. It provides better grounding performance, reduces building penetrations, and simplifies future installations. It also aligns better with the overall intent of the NEC regarding bonding communication systems. Consult with a qualified electrician to ensure the installation meets all applicable codes and regulations. Flag for review