Duct banks are groups of conduits designed to protect and consolidate cabling to and from buildings. In a duct bank, data and electrical cables are laid out within PVC conduits that are bundled together; these groupings of conduit are protected by concrete and metal casings. Duct banks are often buried, allowing contractors to consolidate the wiring for a building into centralized underground paths.
Duct banks are installed for large buildings that require a substantial amount of wiring. This construction method is designed to protect the cabling outside of the building and consolidate it in one area. Duct banks allow a property owner to conceal the cabling of a building underground. Bundling cabling together in buried duct banks makes future construction simpler, since the building's cables are centrally located. Duct banks are also useful for installing cabling underneath roads, parking lots and other areas with existing structures. Duct banks also allow property owners to replace, upgrade or repair existing underground wiring without excavating the entire length of the lines.
Duct banks are built in different configurations that accommodate conduits of varying sizes. Each conduit consists of a PVC pipe that contains the insulated wiring of the building. These conduits are bundled together and surrounded with a protective covering, which is specially designed to prevent damage from water or physical stress. Where the wiring of the duct bank meets the building, a specialized manhole is required to prevent water from entering the building while allowing the conduit to expand and contract without damaging the duct bank.
Duct banks use different types of materials to contain electrical conduits. Most standard duct banks use a protective concrete casing that surrounds the PVC conduits inside; other duct banks use a metal casing. Concrete casings are used in standard construction, while metal casings are used to install duct banks under paved areas or other immovable objects. Duct banks with steel or concrete casings use PVC spacers to separate the internal conduits from the concrete walls of the duct bank. Duct banks with metal casings often use grout or sand as a filler material to stabilize the duct bank, prevent damage to the conduit and help maintain its shape.
The trenches and tunnels used to install underground duct banks require special preparation to provide proper support. Duct banks with concrete casings need a trench prepared with materials capable of supporting the weight of the duct bank while providing adequate drainage. Cabling for ducts buried under existing construction are installed after the duct bank is inserted in the ground. Wiring is drawn through the conduits of the duct bank using guide wires inside the bank; this technique also allows upgrades and repairs on wiring in existing duct banks with minimal digging.