MIL-HDBK-1004/2A
3.3.2
Manholes and Handholes. Use double manholes where electric power
and communication lines follow the same route. Select manholes and handholes
of a suitable type from NFGS-16301.
3.3.2.1 Selection. Factors bearing on the choice of manholes and handholes
are number, direction, and location of duct runs; cable racking arrangement;
method of drainage; adequacy of work space (especially if equipment is to be
installed in the manhole); and the size of the opening required to install and
remove equipment.
3.3.2.2 Location. Place manholes or handholes at street intersections,
where required for connection or splices, and where necessary to avoid
conflict with other utilities. Manhole separation shall not exceed 600 feet
(182.8 m) on straight pulls and 300 feet (91.2 m) on curved duct runs.
Decrease spacing where necessary to prevent installation damage. Limit pull-
in strain to a point that will not damage cable insulation or deform the
cable. A description of maximum permissible pulling forces is given in the
Underground Systems Reference Book.
3.3.2.3 Use. Use manholes for all main duct runs and wherever medium-
voltage cable is installed. Handholes may be used on laterals from manhole
and duct line systems for low-voltage power and communication lines for
building services.
3.3.2.4 Construction of Manholes. Provde manholes not less than 6 feet
(1.8 m) in depth, by 6 feet in length, by 4 feet in width with an access
opening to the surface above (outer air) of not less than 30 inchrs (762 mm)
in diameter. Provide manholes with a minimum wall space of 6 feet on all
sides where splices are to be racked. Duct entrances into the manhole can be
located near one end of long walls so that sharp bends of cables at the duct
mouth are avoided, or else provide sufficient space for a reverse bend before
the cable straightens out on the wall on which the cable is to be racked.
3.3.2.5 Construction of Handholes. Provide handholes not less than 4 feet
(1.2 m) in depth, by 4 feet (1.2 m) in length, by 4 feet (1.2 m) in width with
a standard manhole cover and sump of the same type provided for manholes.
Generally at least four racks should be installed. Where more than two splices
occur, a manhole may be more appropriate. Where splicing or pulling of low-
voltage or communication cables requires an access point, but the volume
provided by handhole is unnecessary, pullboxes may be more suitable for the
installation.
3.3.2.6 Stubs. Provide a set of spare stubs so that the manhole wall will
not need to be disturbed when a future extension is made.
3.3.2.7 Hardware. Select hardware applicable to each installation (refer to
NFGS-16301). Where end-bells are provided, cable duct shields are necessary
only for protection of metallic-sheathed cables.
19
Previous Page
