Can You Put a Direct Burial Cable in a Conduit? A Comprehensive Guide

Direct burial cables are a popular choice for outdoor electrical installations due to their UV resistance and longevity. However, there may be instances where these cables need to be run through a conduit. This article explores the feasibility, benefits, and drawbacks of installing direct burial cables in conduits, as well as the regulatory considerations.

Compatibility and Feasibility

Yes, a direct burial cable can be installed in a conduit. However, this approach is not always the most cost-effective or practical solution. Direct burial cables are designed to withstand environmental factors, but they are typically more rigid and have a larger cross-sectional area compared to standard indoor-rated cables. This makes it more challenging to manage the cables both during installation and post-installation once they are enclosed in the conduit.

Size Considerations

The main challenge with using direct burial cables in conduits is the need for a larger conduit size to accommodate the cable's insulation. For instance, a 2/0 AWG direct burial cable will require a larger conduit diameter (typically 1.5 inches or more) than a standard THHN or THW cable (which might only need a 1-inch conduit).

This oversized conduit not only increases the cost of the installation but also reduces flexibility during installation. The rigid nature of direct burial cables can make it difficult to maneuver them through tight spaces, especially when using 90-degree elbows or Myers hubs for transitions. As one user noted, getting stiff direct burial wire through a 90-degree bend was a challenging job.

Regulatory Compliance

Despite these challenges, there are no specific codes that prohibit the use of direct burial cables in conduits. An electrical inspector may sign off on such installations if the job meets local regulations and the appropriate conduits are used. For instance, one user successfully installed a direct burial cable several hundred feet to a swimming pool pump, then rerouted it through a 90-degree elbow and a Myers hub for the final connection, with no issues from the inspector.

Potential Drawbacks and Cautionary Advice

While direct burial cables can be run in conduits, several factors must be considered. For example, once the cable is installed in a conduit and buried, it can be challenging to replace the cable or conduit without significant disruption. Hardened material in the conduit, such as hardened mud, can obstruct replacement efforts.

In addition, installing direct burial cables in conduits may lead to issues if the cables are run through a drain or other areas where they could obstruct water flow or cause damage. Care must be taken to ensure that the cables are routed away from such susceptible areas.

Regulatory and Local Requirements

Local regulations and electrical codes should also be considered when deciding to run direct burial cables in conduits. Some cables are only suitable for direct burial and must be installed that way if they are to be run underground. For example, if the cable is not designed to be within an active load area (like under an active street), it may not be suitable for installation in a conduit under streets unless the cable is buried to a greater depth, which can be economically impractical.

Conclusion

In conclusion, while it is possible to install direct burial cables in conduits, the process comes with additional costs, challenges, and potential risks. It is important to evaluate the specific requirements of the project and the local regulations to determine whether this method is appropriate. For many installations, standard conduits with appropriate cables may offer a more practical and cost-effective solution.