Local soil conditions, size of the light pole and environmental conditions must be taken into account to design a footing that provides the strength to transfer wind loads into the ground. Undersized footings eventually cause the footing and the light pole to rotate and tilt or lean. A qualified structural engineer should be consulted regarding soil conditions, wind zones and footing specifications during the design and planning phase for the footing.
Concrete footings can be located below grade, meaning the ground must be excavated to pour the footing, or set above ground. In either case, the concrete will be in contact with the soil and ground water, and the type of concrete mixture used will need to take soil content into consideration. For example, Type II Portland cement resists sulfate and is commonly used in the western U.S. due to the sulfur found in that area's soil. A local cement supplier, builder or structural engineer should know what type of concrete mixture to use for local soil conditions. Footings must be allowed to cure properly -- typically at least 72 hours -- before installing a light pole on top of the concrete.
Light pole manufacturers provide a bolt template with each light pole product and instructions on bolt projection. The template accurately locates the bolt circles needed to attach the pole into place on top of the concrete footing. Bolts are placed into the concrete form before the concrete is poured and should be checked for accurate location and projection. Bolts that do not project far enough above the concrete footing will not provide adequate length to secure the pole. Bolts that project too far beyond the footing surface may cause added stress and bending to the bolts, and the pole base plate may not fit properly. A plywood template can be made from the provided bolt template, and the plywood template is placed on top of the footing form to help locate the bolts accurately during pouring.
A light pole manufacturer may require a concrete footing to accommodate an electrical conduit placed through the middle of the footing. The type of conduit used typically is a galvanized metal and is used to manage the light pole's electrical wiring system. The conduit extends from the top of the footing through the concrete, and it curves out to one side to meet the nearest electrical pull box. A typical conduit is at least 1/2 inch in diameter. However, specifics about the diameter and type of conduit needed can be found in the light pole installation and product manual.