When conduits are used as service masts, hubs shall be listed for use with service entrance equipment. This requirement ensures that the hubs meet specific safety and performance standards, as established by recognized testing laboratories such as Underwriters Laboratories (UL) or other nationally recognized testing agencies. The use of listed hubs is critical to maintaining the integrity and safety of the electrical service entrance system.

Importance of Listed Hubs in Service Masts

Service masts are vertical conduits that rise above the roofline of a building to provide a pathway for service entrance conductors from the utility company's overhead lines to the building's electrical service equipment. The hub, which is the fitting that connects the conduit to the service entrance equipment, plays a crucial role in ensuring a secure and weatherproof connection.

Using listed hubs ensures that the components have been tested and certified to withstand the environmental and mechanical stresses they will encounter in service. This includes resistance to weather conditions, such as rain, snow, and UV exposure, as well as mechanical stresses from wind, ice, and the weight of the conductors.

Code Requirements

The National Electrical Code (NEC) provides specific requirements for the use of conduits as service masts. According to NEC Article 230.28, service masts used as supports for overhead service conductors must be of adequate strength or be supported by braces or guys to withstand the strain imposed by the service drop or overhead service conductors. Additionally, the hubs used in these installations must be listed for use with service entrance equipment.

The NEC also requires that service masts be installed in a manner that prevents water from entering the building. This is typically achieved by using weatherproof hubs and fittings that are designed to create a watertight seal around the conduit.

Types of Listed Hubs

There are several types of listed hubs available for use with service masts, including:

1. Raintight Hubs: These hubs are designed to prevent water from entering the conduit, even under conditions of wind-driven rain. They typically feature gaskets or seals that compress when the hub is tightened, creating a watertight barrier.

2. Threaded Hubs: Threaded hubs are designed to screw onto the end of a threaded conduit. They are commonly used in service mast applications because they provide a secure, mechanical connection that can withstand the tension and weight of the service conductors.

3. Set-Screw Hubs: Set-screw hubs use a set screw to secure the conduit in place. While these hubs are less common in service mast applications, they may be used in certain situations where a threaded connection is not feasible.

4. Compression Hubs: Compression hubs use a compression fitting to secure the conduit. These hubs are often used in applications where a watertight seal is required, but threading the conduit is not practical.

Installation Considerations

When installing a service mast with a listed hub, several factors must be considered to ensure a safe and code-compliant installation:

1. Conduit Size and Strength: The conduit used as a service mast must be of sufficient size and strength to support the weight of the service conductors and withstand the mechanical stresses imposed by wind, ice, and other environmental factors. The NEC specifies minimum conduit sizes based on the size and number of service conductors.

2. Clearance Requirements: Service masts must be installed with adequate clearance from other structures, such as roofs, walls, and other buildings. The NEC specifies minimum clearance requirements to prevent contact between the service conductors and other objects, which could create a fire or electrical hazard.

3. Support and Bracing: Service masts must be adequately supported to prevent them from bending or breaking under the weight of the service conductors or the forces exerted by wind and ice. This may require the use of braces, guys, or other support structures.

4. Weatherproofing: The hub and other fittings used in the service mast must be installed in a manner that prevents water from entering the building. This typically involves using weatherproof hubs and sealing any gaps or openings with appropriate sealants.

Common Issues and Solutions

1. Improper Hub Selection: One common issue is the use of hubs that are not listed for service entrance equipment. This can result in a failure to meet code requirements and may compromise the safety and integrity of the installation. To avoid this issue, always verify that the hub is listed for use with service entrance equipment before installation.

2. Inadequate Support: Another common issue is the failure to provide adequate support for the service mast. This can lead to bending or breaking of the mast, which can create a hazardous situation. To prevent this, ensure that the mast is properly supported with braces or guys as needed.

3. Water Intrusion: Water intrusion is a common problem in service mast installations, particularly if the hub is not properly sealed. To prevent water from entering the building, use weatherproof hubs and ensure that all fittings are properly sealed.

4. Incorrect Clearance: Failure to maintain proper clearance between the service conductors and other structures can create a fire or electrical hazard. Always follow the NEC clearance requirements and ensure that the service mast is installed at the correct height and distance from other structures.

Conclusion

When conduits are used as service masts, it is essential to use hubs that are listed for use with service entrance equipment. This ensures that the installation meets the safety and performance standards required by the NEC and other relevant codes. Proper selection, installation, and maintenance of listed hubs are critical to the safety and reliability of the electrical service entrance system. By following the guidelines outlined in this article, electricians and contractors can ensure that their service mast installations are safe, code-compliant, and capable of withstanding the environmental and mechanical stresses they will encounter in service.