Trystan Casey
Digging a trench for electrical conduits by hand can be a challenging and laborious task, but it is possible with the right tools and preparation. Before beginning any work, it is important to understand the electrical code requirements, trench depth options, conduit material, and the type of electrical wire to be used. The National Electrical Code provides guidelines for wiring methods, materials, and safety considerations. It is also crucial to determine the amount of current needed, both for the present and future, to decide between using conduit or cable.
| Characteristics | Values |
|---|---|
| Trench depth | Depends on the type of conduit, wire or cable. For instance, PVC conduit with individual insulated wires should be installed at 18 inches depth. |
| Trench width | Should be wide enough to accommodate the conduit. For instance, a 4-inch ditch is sufficient for a power-only trench. |
| Tools | Shovel, trenching shovel, mattock, trenching spade, trencher, hammer drill, electric jackhammer, pickaxe, gas tiller, bar, hammer |
| Soil type | Rocky soil or heavy clay soil is difficult to dig by hand. |
| Permits | Required before beginning work, can cost between $10-500 |
| Inspections | Required after work is completed |
| Conduit material | Schedule 40 PVC, EMT, galvanized rigid metal |
| Conduit bedding | Minimum 4 inches of sand if dug through rocky terrain |
| Conduit diameter | Primary conduit (7200V) must be 3 inches in diameter with 36-inch radius long sweeping elbows at any 90-degree bend |
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Hand trenching tools
The most basic hand trenching tool is a trenching shovel, which has a pointed tip for slicing into the ground and squared sides for creating smooth trench walls. Drain spades, which are a type of shovel with a rounded tip and curved sides, are useful for shaping the trench after the initial excavation. For breaking soil and chopping roots, a pick mattock can be used. This tool has a head with a pickaxe on one side and a mattock blade on the other. Grub hoes, or trenching hoes, are another type of hand trenching tool. They have a long handle with a sharpened blade on the end and are used for breaking up and tilling soil, as well as digging deep, narrow trenches. For removing loose soil from the bottom of the trench, a clean-out shovel can be used.
For small projects, such as installing electrical wiring for a conduit, handheld power trenchers can be used. These tools are lightweight and easy to transport, and they can typically dig 10 to 20 inches deep. Handheld trenchers can have a wheel or chain blade. Edging trenchers are another type of handheld trencher that digs small trenches up to a few inches deep next to flower beds and paths to install edging material. Cable installers are machines that dig a trench up to 7 inches deep, install wire, and then cover it. Walk-behind trenchers are also available for creating shallow, narrow trenches with less effort and more precision.
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Trench depth
Additionally, the type of soil can impact the trench depth. If you have granular soil that is easy to dig, you may opt for a deeper trench to reduce the need for expensive electrical materials like metal or plastic conduits, which protect the wiring from physical damage. Conversely, if you encounter rocky soil, heavy clay, or extensive tree roots, you may need to adjust your trench depth accordingly.
It is also important to consider the frost line of your area, especially when installing plastic conduits for a permanent installation. PVC conduits can be susceptible to freezing temperatures, so placing them below the frost line can help prevent damage.
To ensure compliance with local regulations, it is advisable to refer to the National Electrical Code (NEC) and local electrical codes, as they provide guidelines for burial depths and standard operating procedures. Additionally, remember to call your local utility companies before digging to avoid damaging any underground utilities.
Lastly, when determining trench depth, consider the width of the trench as well. OSHA recommends a minimum trench width of 18 inches for electrical wires to ensure compliance with safety standards.
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Conduit material
There are seven common types of electrical conduit materials, which can be broadly categorized into metal conduits and non-metal conduits. Metal conduits are typically made of stainless steel, coated steel, galvanized steel, or aluminum. They offer solid protection and are suitable for providing structural support. Rigid metal conduits (RMC) are thick-walled and provide excellent protection against impacts and severe damage. They are often used outdoors and in industrial or commercial buildings. Intermediate metal conduits (IMC) are a thinner and lighter version of RMC, making them easier to work with in construction. Electrical metallic tubing (EMT) is another type of metal conduit that is lighter, thinner, and more bendable than RMC.
Non-metal conduits, on the other hand, are typically made from polyvinyl chloride (PVC) or plastic. They are flexible and suitable for outdoor residential applications. Schedule 40 PVC is commonly used for direct burial or encasement in concrete. It is important to note that PVC may not be suitable for extremely cold climates as it can become brittle at low temperatures. Flexible metal conduit (FMC) is made of coiled self-interlocked steel or aluminum strips, allowing for bends and twists without the need for extra hardware. Liquid-tight flexible metal conduit (LFMC) is a variation of FMC with sealed fittings and a plastic coating, making it suitable for wet areas. Electrical non-metallic tubing (ENT), also known as "smurf tube," is a flexible, corrugated plastic tubing that is moisture-resistant and flame-retardant and commonly used indoors.
When choosing a conduit material, it is essential to consider the specific requirements of your project, including the climate, weight loads, soil conditions, and drainage. Additionally, it is crucial to comply with the National Electrical Code (NEC) and any applicable local code rules to ensure a safe and effective installation.
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Electrical wire type
When it comes to electrical wire types, there are several options to consider for your hand-dug trench:
Teck90 Cable
If you use Teck90 cable, you can skip the conduit. Teck90 cable is code for direct burial, and you'll need to place a pressure-treated 2x6 on top to prevent shovel damage. This option is mentioned by users in Western Pennsylvania.
Underground Feeder Cable (UF Cable)
UF cables are designed for direct burial without a conduit. They are typically used for residential outdoor lighting and landscaping installations. UF cables should be installed 12 inches deep for GFCI-protected cable and 24 inches deep without GFCI protection or conduit.
PVC Conduit with Individual Insulated Wires
PVC (Polyvinyl Chloride) conduit is a popular choice for protecting electrical wiring underground. It is available in Schedule 40 and Schedule 80 variants. Schedule 40 PVC is suitable for underground use, while Schedule 80 PVC is often required above ground.
When using PVC conduit with individual insulated wires, the recommended depth is 18 inches. The wires must be rated for use in wet locations, such as Type THWN-2 (thermoplastic/wet location/nylon jacket).
Galvanized Rigid Metal Conduit
Install galvanized rigid metal electrical conduit with individual insulated wires at a depth of six inches. Similar to the PVC conduit method, the wires are pulled through the conduit once the entire conduit run is complete.
The specific wire type and installation depth may vary depending on your local electrical code and the characteristics of your soil. It is essential to consult the National Electrical Code and local building inspection departments for detailed requirements and guidelines.
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Backfilling
Firstly, it is essential to inspect the trench and conduit before backfilling. This inspection ensures that the installation meets the required standards and codes. Once the inspection is approved, the backfilling process can begin.
The backfilling material should be chosen carefully. In most cases, the excavated soil can be used for backfilling. However, if the soil is rocky or uneven, it may be necessary to use alternative materials such as sand or gravel to ensure a stable bed for the conduit. It is recommended to wet the clay to create a soft mixture that can be easily squished underneath the conduit for added support.
When backfilling, it is important to ensure that the trench is compacted and levelled properly. This can be achieved by tamping down the backfill material in layers. For larger trenches, machinery such as a tractor with a plow may be used to help compact the backfill.
It is also crucial to ensure that the conduit is protected during the backfilling process. This includes ensuring that the conduit is properly bedded and supported to prevent damage from the backfill material. Any caution tape or mule-tape should be left in place during backfilling, and care should be taken not to damage these components.
Finally, once the trench has been backfilled and compacted, it is important to check that the conduit is still at the correct depth and that the backfill is secure and stable. This may involve checking for any voids or air pockets and ensuring that the surface is ready for any planned usage, such as driving or construction.
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Frequently asked questions
You can use a shovel, mattock, trenching spade, or trencher.
The depth of your trench depends on the type of conduit, wire, or cable you are using. For example, galvanized rigid metal electrical conduit should be installed 6 inches deep, while PVC conduit should be installed 18 inches deep.
The type of conduit you use depends on your specific use case. For example, EMT electrical metallic tubing is not meant for in-ground use, while Schedule 40 PVC is suitable for underground direct burial or encasement in concrete.
Yes, installing new electrical outlets, adding wiring, and altering low-voltage systems require a permit. Permits can cost anywhere from $10 to $500 and you should plan to get your permit at least two weeks in advance.
Hand digging can be hard work and brutal on your body, especially if the soil is rocky or frozen. Consider your current health and the type of soil you will be digging in before deciding to trench by hand.
