MARMON VITALink MC, Руководство по установке

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When all conductors are the same size, the
equation becomes:
T
c
= K x F x kcmil x N
kcmil = Circular mil area of one conductor
in thousand circular mils (kcmil)
N = Total number of conductors pulled
The tension distribution factor (F) is 1 for a sin-
gle multiconductor cable, 0.8 when pulling
more than one cable of equal conductor size,
and 0.6 when pulling multiple cables of unequal
conductor size. Ground wires and armor should
not be considered in these computations. The
conductor circular mil area, and the conductor
strength for one and three annealed copper
conductor(s) of a single cable (N=1 and 3, and
F=1) using the above equation is provided in
Table 3.
Cable Attachment Limit
The maximum allowable tension is also limited
by the ability of the device used to connect the
cable to the pull rope to withstand the forces
applied. When pulling by gripping the conduc-
tors with a pulling eye or bolt, the maximum ten-
sion is usually limited to 10,000 pounds. This is
dependent upon the pulling eye or bolt used
and the method of application. The manufac-
turer’s recommendations should be followed.
When the insulated conductors are gripped with
a properly sized and applied basket weave grip,
the limit is 200 pounds per grip. This is based
upon the hoop stress applied with a basket grip
and the cable construction. Since the attachment
by a grip is limited by the slip of the insulation,
the insulation may be removed, and friction tape
applied over the conductor to increase the pull
by grip limit. For this configuration, with a properly
sized and applied grip, the limit is 2000 pounds.
Sidewall Pressure
When a cable is pulled around a bend, radial
force is exerted on the insulation, armor, and
jacket as the cable is pressed against the inner
arc of the bend (see Figure 4). This is referred
to as sidewall pressure and is expressed as
pounds per foot of radius.
Sidewall pressure is important in cable pulling
calculations for two reasons. The first is its
increase in the total pulling tension due to
greater pressure between the cable and the
bend. The second is its crushing effect upon the
cable insulation and the possibility of permanent
damage to the insulation and/or the cable armor
if excessive sidewall pressures are permitted.
Sidewall pressure is usually the determining
factor when establishing maximum allowable
pulling tension for large conductor sizes.
The maximum value for sidewall pressure
depends on the cable design. For VITALink MC
it is normally 400 pounds per foot of bend, with
a 10 times pulling radius multiplier. Under cer-
tain circumstances it may be necessary to
reduce the bend radius multiplier to 7 times
(which is provided for permanent training). For
this case, the sidewall pressure should not
exceed 300 pounds per foot of bend. The for-
mula for sidewall pressure for a single cable is
as follows:
Tp = SWP x R
Tp = Maximum allowable tension which
will not exceed the sidewall pressure
limit in pounds*
SWP = Sidewall pressure limit in
pounds per foot
R = Radius of bend in feet
* This value may be more limiting than the
maximum tension Tc based on conductor
strength. The lower value of the two governs.
Radius Of Bend
Sidewall Pressure
Tension
Figure 4. Sidewall Pressure