What Is Direct Burial Cable? Benefits, Installation Tips, and Application

Underground electrical systems require cables that can withstand soil contact, moisture temperature variations, as well as the physical pressures associated with underground installations. The standard indoor wire isn't made to handle these conditions. This is why the direct burial of cable becomes crucial. 

Direct burial cables are specifically designed to be installed directly into the ground without needing an entire conduit system for the entire length. The product you choose to use it could be used to distribute power for utilities electric service for residential homes, electrical services outdoor lighting pumps, workshops communications networks, and many different underground uses. 

But "direct burial" does not mean that there is a universal type of cable. Aluminum URD, U-B, USE-2, medium voltage cable, cable for communication and a variety of other cables may have direct burial ratings, however they all have different constructions specifications, voltage ratings, permissible places, and requirements for installation. 

Understanding the differences is crucial to make the right choice when selecting underground electrical cables for residential industrial, commercial, agricultural or utility project. 

What Is Direct Burial Cable? 

Direct burial cables are a wire or cable analyzed for direct burial in soil. Its outer jacket, or insulation is designed to withstand the harsh conditions typically encountered underground. 

UL Solutions explains that cable that is tested for underground burial can be identified by marks like "FOR DIRECT BURIAL," "DIRECT BURIAL," "DIR BUR," or "DIR BURIAL." The labeling on the cable, label on the reel, its packaging and the specifications of the product must all be scrutinized to determine their permissible uses and restrictions. 

Direct burial cables are constructed to resist: 

These characteristics do not mean that the cable is unbreakable. It is still susceptible to damage through sharp rocks, inadequate backfilling, excess pulling tension, poor installation, digging equipment, or faulty terminations. 

How Is Direct Burial Cable Constructed? 

Construction is different for each of the cable types. A typical cable may comprise one or more cores that are conductive covered with insulation, fillers that protect and shielding, armor or a jacket overall. 

Conductors 

Direct burial cables may contain: 

Aluminum is extensively used in primary and utility power distribution due to its an ideal balance between conductivity weight, cost, and weight. Copper is commonly used for smaller branch circuits, pumps landscape systems, controls and communications. 

Insulation and Jackets 

The most common insulation materials and the jackets comprise: 

For instance Global Cable and Wire's one-conductor URD cable is a 1350-H19 series aluminum conductor that has black XLP insulation. This product is specifically designed for secondary distribution circuits that are 600 volts used in underground ducts as well as direct burial applications. 

The UF-B cable has a distinct construction. Cerrowire's product UF-B has copper conductors in a moisture-resistant PVC assembly. It is suitable for underground feeder and branch circuit use, as well as direct burial. 

Simply putting ordinary indoor cables in the trench is not going to mean it is suitable to be used underground. The cable should have the proper rating and designation of the type for the whole installation. 

Common Types of Direct Burial Cable 

Aluminum URD Cable 

URD means underground residential distribution, although these products are also used in commercial, agricultural, and utility secondary-distribution systems. 

Direct burial aluminum cable can be purchased in the following manner: 

It is typically utilized in conjunction with transformers or service equipment, structures and underground distribution points for utilities. 

Global Cable and Wire's aluminum URD 600-volt products are specifically designed for secondary distribution circuits. They can be used in ducts or direct burial applications according to the published specifications. 

A cable that is described as URD is not to be considered to be suitable for all element of a building wiring. Certain distribution products for utilities have limitations on indoor usage in the absence of other designations, such as RHH or the RHW-2 or any other recognized building-wire classification. 

UF-B Cable 

The term UF-B is a reference to underground feeders and branches-circuit cables. 

It is often employed for small residential or light commercial projects like: 

Type UF-B is able to be installed underground, with direct burial when it is it is used in accordance with its ratings and with the necessary overcurrent protection. Certain UF-B models can be installed in moist dry, corrosive, or dry areas as per the relevant electrical code. 

USE and USE-2 Cable 

USE refers to underground service entry. The USE-2 cable is designed to be used for underground service and is certified as direct burial. 

Products that bear RHH, USE-2, and RHW-2 markings can provide more installation rights than cables identified as USE. Cerro wire claims that its USE-2/RHH/RHW-2 cables can be used to provide underground service entrance as well as direct burial in dry or wet areas within the temperature limit they have specified. 

Always verify whether the cable is able to continue within the structure or must be terminated at an approved place. 

Medium-Voltage Direct Burial Cable 

Medium-voltage cable is utilized in industrial, utility campus, renewable-energy and commercial distribution systems. 

They could comprise: 

Medium-voltage installations require specific design, equipment as well as testing and termination processes. They must be handled by experienced professionals who are familiar with the voltage of the system and the cable class. 

Direct Burial Communication Cable 

Direct burial cables are not all the same. Not every direct burial cable has electrical power. Direct burial-rated products can also be used for 

For instance, Southwire's direct-burial Category 6 cable can be used for burial without or with conduit, and exposure to sunlight as well as water. 

Cables for power and communications must be separated and selected in accordance with their respective ratings as well as the installation requirements applicable to them. 

Benefits of Direct Burial Cable 

1. Reduced Need for Continuous Conduit 

One of the main benefits is that properly certified cable can be inserted directly in the trench, without surrounding the entire route with conduit. 

This may be a reduction of: 

Conduit might still be needed or suggested if it emerges from ground, is buried through traffic areas, is inserted into the building or crosses a foundation or needs protection from physical damage. 

2. Resistance to Underground Conditions 

Direct burial materials are designed to work in damp and subterranean environments. Based on the type of product, their jacket or insulation is able to withstand erosion, soil contact and other environmental stressors. 

The exact characteristics vary according to the cable's specifications. Therefore, the specs must be verified rather than thinking that all direct burial devices have the same security. 

3. Cleaner Property Appearance 

Underground cable is free of visible overhead spans and poles or aerial service wires on the way. 

This can be useful to: 

4. Less Exposure to Wind and Falling Objects 

Buried cable isn't directly exposed to winds or tree branches and ice accumulation. It is also not exposed to overhead contact with vehicles. 

It is still susceptible to being damaged due to digging and ground movement rodents and sharp backfill as well as future construction that is why the correct bed, depth routes, documentation of the route, and warning protection are essential. 

5. Flexible Power-Distribution Options 

Direct burial cable comes in a variety of size, voltage class and configurations. This makes it suitable to use in everything from tiny lighting circuits to huge secondary utility distribution projects. 

Common Direct Burial Cable Applications 

Residential Underground Service 

Direct burial cables can connect an electric utility transformer or distribution point to residential equipment for service. 

URD and USE-type devices are generally considered to be suitable to be suitable for these installations, based on the specifications of the utility and the markings on the cable. 

Detached Garages and Workshops 

UF-B or a different underground feeder can provide lighting, receptacles and heating equipment, tools, and subpanels for detached structure. 

Size of cable must be determined on the calculated load, distance of the circuit and voltage drop and the installation conditions. 

Commercial Buildings 

Commercial direct burial cable may supply: 

Larger commercial installations could use triplex or quadruplex aluminum URD assembly, single conductors, and engineered medium-voltage systems. 

Agricultural Properties 

The farms and agricultural enterprises can use buried electrical cables to: 

The conditions of the soil, the moving heavy equipment long distances, and electrical loads should all be taken into consideration during the design process. 

Outdoor Lighting 

Direct burial cable is typically used to: 

Landscape cable with low voltage and high-voltage lighting feeders are distinct categories of products and cannot be used in conjunction with each other. 

Pumps and Water Systems 

Pumps for wells and drainage pumps, irrigation systems and various other equipment might require direct burial or wet-location conductors. 

A general direct burial marking does not mean that an item is approved for submersible pumps. UL states that a cable that is evaluated specifically for use in pumps is identified as such. 

Utility Secondary Distribution 

Aluminum URD cables are widely utilized in secondary distribution between service points, transformers utility pedestals, transformers, and the rest of underground machinery. 

The circuit may have one or more, two, three or four conductors, depending on the electrical system. 

Direct Burial Cable Installation Tips 

Underground electrical work must be planned and executed by trained professionals. These guidelines will help to reduce the chances of problems with installation. 

Confirm the Cable Marking 

Make sure you check the cable's surface, the reel tag packaging, and the technical data sheet to determine: 

UL suggests reviewing all product labels and category information to determine a product's ratings and restrictions. 

Verify the Required Burial Depth 

There isn't one burial depth that can be used for each project. Specific requirements depend on: 

Southwire's installation guidelines state that the depth of burial should shield the cable from surface activity. The guide also mentions that conditions of frost or unfinished grades could require an additional depth, while the approved protection supplemental to it could affect the design of the installation. 

Don't trust general depth recommendations from online sources without looking up the requirements of the particular project. 

Call Before Digging 

Existing gas, electric water, sewerage communication, as well as other underground services must be identified prior to excavation beginning. 

The proposed route needs to be modified as needed to ensure clearances remain in place and not interfere with existing utilities. 

Prepare a Smooth Trench 

Sharp rocks, construction debris and uneven trench bottoms may harm the insulation of cables. 

Southwire suggests an even trench bottom constructed of sand or earth that has been well-tamped. In soil that is rocky the cable should be positioned on a protective backfill and the area around the cable should be clear from anything that can cause damage. 

Avoid Excessive Pulling and Bending 

The cable can get damaged in the process of installation prior to when it is turned on. 

Installers must adhere to the limits set by the manufacturer on: 

The cable shouldn't be dragged across sharp edges or squeezed around bends in a tighter radius than the permissible radius. 

Use Conduit Where Additional Protection Is Needed 

Even if the cable has been certified for direct burial, the conduit could be advantageous or necessary at 

Southwire suggests conduit as a the best practice for vehicular and pedestrian traffic routes. 

Install Warning Protection 

Safety tape, warning tape marking routes, warning tape, or any other acceptable identification method can be used to alert future excavators to the presence of electrical cables. 

The final route must be recorded before the trench is sealed. 

Use Compatible Terminations 

Conductors made of aluminum and copper need connectors and equipment that are matched to the conductor's material and size. 

Installers of aluminum cables should adhere to the appropriate guidelines for: 

Incorrectly installed connections could cause excessive heat, voltage loss or even equipment failure. 

Protect Splices and Transitions 

Underground splices should be made using specific products designed specifically for the particular environment and the type of cable. 

The indoor wire nuts, the ordinary tape, or enclosures that are not listed are not substitutes for the approved underground-splicing equipment. 

Test Before Backfilling 

Based on the specific project, testing could be: 

Identifying damage prior to the trench being filled can save you from costly excavations in the future. 

Common Direct Burial Cable Mistakes 

Assuming All Outdoor Cable Can Be Buried 

Sunlight-resistant or outdoor-rated cables are not always direct burial-rated. Find the right name and the appropriate documentation. 

Using the Wrong Cable Inside a Building 

Certain URD as well as USE products come with limitations after they have entered the building. The combination of ratings like RHH/RHW-2 are sometimes needed for specific raceway installation. 

Choosing Cable Size Only by Ampacity 

Conductor selection also needs to consider the voltage drop, length of route and terminal ratings and load characteristics, as well as conditions in the surrounding, as well as the installation methods. 

Ignoring Future Surface Use 

The area that is landscaped could later be transformed into a driveway, patio, extension of a building, or even a route for heavy equipment. Planning for installation should take into account the current and likely usage. 

Backfilling With Rocks and Debris 

The impact of sharp or heavy materials can cause damage to insulation during backfilling or even as the ground gets settled. 

Failing to Record the Route 

The recording of the cable's location can help lower the risk of damage from an accident during the next maintenance or construction. 

How to Choose the Right Direct Burial Cable 

Before placing an order, verify: 

Order Direct Burial Cable From Global Cable & Wire 

Global Cable & Wire supplies direct burial aluminum cables in a variety of sizes and configurations suitable for underground power distribution. 

There are many options to choose from: 

For instance, its for instance, the 1/0 Harvard URD cable is a 600-volt conductor made of XLP that is specifically designed to be used as a secondary distribution cable for direct burial or duct installations. The product page provides conductor construction dimensions, outside diameter the weight, standards and ampacity-specific information for the application. 

Before buying, verify the type of cable, conductor configuration and voltage, as well as the installation method as well as the required listing and length of the cable with the electrician, project engineer or utility with authority. 

Frequently Asked Questions