Calculating How Deep to Bury Outdoor Electrical Wire
You may plan to install electrical wire outdoors for operation of pumps, lighting, and other apparatuses. Whatever the purpose, you can run your wiring overhead or in a below-ground trench. If you choose a trench, you will need to know what types of wiring and conduits you can use and how deep to bury them. Below, you will find five tips about electric wire burial.
Before getting over-involved, however, you should check the local and municipal laws and regulations on cable burial, and with the local utilities so they can mark where their underground utilities lie on your property. Before starting any of the work, you should also apply for a construction and electrical permit, as it could be required in your municipality.
1. Direct Cable Burial
UF cable (underground feeder cable) is specially designed and manufactured with properties that make it ideal for burial. This cable should be buried at a depth of 24 inches. The cable is less likely to be cut or disturbed by typical digging if it is this far below ground. However, certain municipalities and states/provinces require that local utilities be contacted so that they can mark where their undergrounds utilities lie on your property.
When purchasing UF cable, you should take special care to differentiate it from ordinary NM (non-metallic, or Romex) cable. Usually, UF cable has information printed on the sheathing that identifies it as UF.
2. Using UF Cable Above Ground
Although UF cable is designed to be buried, you can also use it above ground. For example, if you have a run of cable that is partly buried and partly above the ground, and you prefer not to splice your burial cable to a length of above-ground cable, you can use UF cable for the full cable run. Keep in mind, though, that any UF cable used in above-ground applications should be run through conduit where it can be damaged.
3. Electrical Wire Encased in PVC Conduit
The National Electric Code (NEC) sets the required burial depth of electric wire in rigid, non-metallic conduit, such as PVC, at 18-inches. Cable in any conduit, including PVC, that is buried at this depth is not in danger of being severed or disturbed by normal digging. However, keep in mind that no cable or conduit is protected from digging by construction equipment such as trench diggers or backhoes.
4. Electrical Wire in Rigid Metal Conduit
Owing to the durability of rigid metal conduit, you can bury electrical wire in this conduit at a shallower depth. According to the NEC, you can bury it at a depth as shallow as 6 inches.
5. Electrical Wire Encased in Flexible Metal Conduit
If you wish to use flexible metal conduit, be sure it is watertight.
Calculating How Deep to Bury Outdoor Electrical Wire FAQ
How deep should outdoor electrical wire be buried?
The depth at which electrical wires should be buried in the ground varies by how much voltage the wire receives, which can make things a bit tricky.
Low-voltage wire that carries no more than 30 volts of electricity must be at least six inches deep. If wires are carrying 240 volts of power, on the other hand, they must be at least 18 inches below the surface.
Another factor is the electrical codes, which vary on a state-by-state and sometimes a city-by-city basis. To find out exactly how deep wire should be buried to comply with the laws where you live, call your local housing authority to find out exactly what the requirements are.
How do you dig a trench for electrical wire?
It is a much neater look when electrical wires are buried underground and it keeps the wire safer from weather damage as well. However, burying electrical wires means you have to dig a trench to bury them in.
If the ground is very hard and the soil tightly compacted, loosen it up first with a mattock. Use this to break up the soil where you plan to dig.
Once the soil is loosened, start digging out the trench with a trenching spade. It's a good idea to use chalk lines to mark out the width of the trench first, so you don't end up digging more than you have to.
How wide does a trench need to be for electrical?
When you are digging a trench to bury electrical power lines, it is not only the depth of the trench you should worry about. You also need to know how wide the trench should be, a question that is not always easy to answer.
Electrical codes vary by state, so what you are required to do is not the same in every geographic location. However, OSHA has laid out very clear guidelines for electrical trenches, so you can refer to this.
OSHA recommends a trench width of at least 18 inches for electrical wires. At this width, you will likely stay compliant with any state or city electrical codes as well.
Do electrical wires need to be in conduit?
Outdoor electrical wires that are buried underground are not necessarily required to be in conduit, which is a protective shell that surrounds the wires to protect them from environmental damage.
Since state and city electrical codes vary and since there are different code requirements for electrical wires at different voltages and different depths, you may not always be required by law to place wires in conduit.
However, it is highly recommended that you do so. Conduit keeps wires protected from moisture, dirt, animals, and other environmental factors that can cause damage to the wires.
Can water and electric be buried in the same trench?
Digging a trench is such a hard job and takes so much time, you might want to use the same one for water lines and electrical wires. And you absolutely can use a joint trench to run both water and power, but you must do so safely.
Industry experts recommend placing water pipes at least 12 inches away from electric lines. This means you will need a very wide trench, but there are some cases where this might be the most effective solution.