Duct Bank Design Guide

In order to properly size the duct bank the following factors must be considered and evaluated.

Duct bank design guide.

System design and performance requirements 1. Ductwork standard design we can see from the velocity colour scale and the streamlines that in the design on the left the inlet air directly strikes the sharp turns that are present in the system which causes an increase in the static pressure. Design all underground electrical raceways and duct banks for seismic zone 2. Lengths of secondary duct banks shall be minimized to limit pulling distances and electrical losses.

Contractor shall have class a 17 license for minimum of 2 years prior to work. Concrete shall be red dyed utilizing red dye mixed into the concrete for a minimum of 5 minutes prior to pouring. Duct banks are to terminate in a service entrance switchboard or switchgear within 5 of entering the building or are to remain in concrete and painted red until terminated in a service entrance rated disconnect. Minimum space between ducts.

Use schedule 40 rigid pvc. Electrical engineers designing electrical duct banks must understand the soil s thermal properties and the effects it will have on the overall installation. Service entrance mv and lv duct banks are to be concrete encased. Use walls of trench to form side walls of duct bank where soil is self supporting and concrete envelope can be poured without soil inclusions.

Underground concrete encased electric conduit duct banks shall consist of type db 60 polyvinyl chloride pvc conduit rated for 90 c cable and meeting nema standard tc 6 and astm f 512 for underground applications. Any secondary duct lengths. Where elbows are required to transition from horizontal to vertical for stub ups use rigid steel conduit sweep elbows. 3 inches between ducts and exterior envelope wall between 2 inches ducts for like services and 4 inches between power and signal ducts.

B concrete encased ductbanks in all other areas. Reinforcement of concrete is not required. Minimum of 1 bag of dye per 1yd of concrete. The minimum allowable concrete duct compressive strength is 5 000 psi at 28 days.

Duct banks is 3 feet below grade measured to top of ductbank. Use bell adapters where conduits enter manholes. Top of conduit conduit bank.