measured to the elevation prescribed for the bottom ofthe duct, plus the thickness of the concrete encase-ment, if any. In an underground power system, thebottom of the manhole is usually about 2 feet belowthe bottoms of the incoming and outgoing ducts.Power and communications manholes are often com-bined; figure 10-22 shows plan and section views of acombination power and communications manhole.Conduit and cable connections to buildings,street-lighting systems, traffic light systems, andthe like, are low-voltage secondary lines. Ductconnections from main-line manholes run to small-subsurface openings called handholes on the sec-ondary line. The handhole contains connections fortakeoff to the consumer outlet. Figure 10-23 showsplan and section views of a handhole.Construction SheetsSeveral construction situations have been men-tioned in which line and grade for construction areobtained from a line (or perhaps from two lines) ofFigure 10-22.—Combination power and communication manhole.10-22
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