Okay, let's break down the intersystem bonding requirements for your 8-unit townhome project in Washington State, considering your service location, conduit runs, and low-voltage provisions.

Understanding Intersystem Bonding (NEC Article 250.94)

The purpose of intersystem bonding is to create a low-impedance path between the power grounding electrode system and the grounding systems of communication services (like phone, cable TV, and internet). This helps minimize voltage differences between the systems, reducing the risk of damage from lightning or power surges and improving safety.

Key Considerations for Your Project1. Location of the Intersystem Bonding Termination

The intersystem bonding termination (a listed connector suitable for connecting to multiple grounding conductors) must be accessible and located at the service equipment or metering equipment enclosure. In your case, this means the intersystem bonding termination needs to be at the service disconnect/meter stack location, not at the exterior J-box where your feeder conduits and low-voltage stubs terminate.2.

Bonding Conductors

Each communication service (Cat6 for internet, RG6 for cable TV, and telephone if present) must have its grounding conductor connected to the intersystem bonding termination. The size of the bonding conductor must be in accordance with NEC Article 250.66 and 250.
94. It's typically sized based on the size of the service entrance conductor. A common size is #6 AWG copper, but always verify based on your specific service size. The bonding conductor can be insulated or bare, and must be securely connected to the intersystem bonding termination.3.

Accessibility and Identification

The intersystem bonding termination must be readily accessible for inspection and maintenance. It needs to be identified with a permanent label stating "Intersystem Bonding Termination Here" or similar language.4.

Grounding Electrode System Connection

The intersystem bonding termination is connected to the power system grounding electrode system (the one for your electrical service). This is typically via the grounding electrode conductor that runs from the service equipment to the grounding electrode (e.g., ground rod, concrete-encased electrode, or metallic water pipe).

Specific Requirements for Washington State Washington State adopts the National Electrical Code (NEC) with some state-specific amendments. It's essential to consult the latest Washington State Electrical Code (WAC 296-46B) to check for any local modifications or interpretations of NEC Article 250.94. You can usually find this information on the Washington State Department of Labor & Industries website. Keep in mind that local jurisdictions (cities and counties) may have their own requirements or interpretations, so it's wise to check with the local electrical inspector's office.

Applying to Your Situation1. Intersystem Bonding at the Service

You must install the intersystem bonding termination block (or suitable connector) at the service disconnect/meter stack location.2.

Running Bonding Conductors

Run a bonding conductor (sized appropriately, likely #6 AWG copper) from the intersystem bonding termination at the service location to the exterior J-box. This becomes your central bonding point for the low-voltage services.3.

Connecting Low-Voltage Grounds at the J-Box

Connect the grounding conductors from your Cat6 and RG6 cables to the bonding conductor that you ran from the service location. Make sure the connections are secure and listed for grounding.4.

Microduct Considerations

If your microduct system has any metallic components (e.g., metallic shielding), it should also be bonded to the same grounding conductor.

Why This Approach is Necessary NEC Compliance

Placing the intersystem bonding termination at the service equipment ensures compliance with NEC 250.94.

Effective Bonding

A continuous, low-impedance path back to the service grounding electrode system is crucial for minimizing voltage differences and providing effective protection.

Accessibility

The service location is typically more accessible for inspection and maintenance compared to a potentially buried or less-accessible exterior J-box.

Important Notes and Recommendations Consult with the Local Inspector

Always discuss your plans with the local electrical inspector before starting the work. They can provide specific guidance based on local interpretations and conditions.

Follow Manufacturer's Instructions

When installing grounding and bonding equipment, carefully follow the manufacturer's instructions for proper installation and torque requirements.

Use Listed Equipment

Ensure that all grounding and bonding connectors, clamps, and other equipment are listed by a recognized testing laboratory (e.g., UL).

Document Everything

Keep detailed records of your grounding and bonding system, including the size and type of conductors used, the location of the intersystem bonding termination, and any other relevant information. This documentation will be helpful for future inspections and maintenance.

Consider Surge Protection: While intersystem bonding is important, it's also recommended to install surge protection devices (SPDs) at the service entrance and at the individual units to provide additional protection against transient voltage surges.By following these guidelines and working closely with your local electrical inspector, you can ensure that your 8-unit townhome project has a safe and code-compliant intersystem bonding system. Remember, electrical work can be dangerous, so always prioritize safety and consult with qualified professionals when needed. Flag for review