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 six tips about electric wire burial.
Before getting over-involved, however, you should check the local and municipal laws and regulations on cables 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 the type that is watertight.