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