| Definition of Terms "Training" is the positioning of the cable when NOT
under tension.
"Bending" is under tension. The minimum
bending radius applies to the inner surface of the cable and not to the cable axis.
"Sidewall pressure" or loading is the
radial force exerted on a cable when pulled around a bend or sheave. Excessive sidewall
pressure will crush the cable.]
Sidewall Loading
Where T is tension out of a bend, in pounds and R is radius
of a bend, in feet:
| 1-1/C per conduit: |
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| 3-1/C cradled: |
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| 3-1/C triangular: |
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| Typical Sidewall Loadings |
Lbs/Ft |
| 600V nonshielded control |
300 |
| 600V & 1 K V nonshielded EP and XLP |
500 |
| 5 & 15 K V Unishield & EP / XLP |
500 |
| 25 - 35 K V power |
300 |
| Interlocked armored cable (all voltage classes) |
300 |
Minimum Bending Radii
Power Cables without Metallic Shielding, up to 600 V
The minimum bending radii for both single and
multiple-conductor cable with or without lead sheath and without metallic shielding are as
follows:
Thickness of
Conductor Insulation |
Minimum Bending Radius as a Multiple of Cable Diameter
Overall Diameter of Cable (Inches) |
| (in Mils) |
1,000 and
less |
1,001 to
2,000 |
2,001 and
over |
| 155 and less |
4 |
5 |
6 |
| 170 to 310 |
5 |
6 |
7 |
| 325 and over |
- |
7 |
8 |
Power Cables with Metallic and Lead-Covered Shielding
(all voltages)
- For Tape Shielded Cables, the minimum bending radius is twelve
times (12) the overall diameter of the completed cable.
- For Wire Shielded Cables, the minimum bending radius is eight
times (8) the overall diameter of the completed cable.
Power Cables over 600 Volts, Non-Shielded, Non-Armored
- The minimum bending radius for all cables is eight times
(8) the overall cable diameter.
Interlocked Armored Cable (all voltages)
- The minimum bending radius for cables with non-shielded
conductors is seven times (7) the armor overall diameter.
- The minimum bending radius for cables with shielded
conductors is twelve times (12) the diameter of one phase conductor or seven
times (7) the armor overall diameter, whichever is larger.
Pulling Tensions
The following recommendations are based on a study
sponsored by ICEA. These recommendations may be modified if experience and more exact
information so indicate.
A. Maximum Pulling Tension on Cable
- With pulling eye attached to copper conductors, the maximum
pulling tension in pounds should not exceed 0.008 times cir-mil area.
- With pulling attached to aluminum conductors, the maximum
pulling tension in pounds should not exceed 0.006 times cir-mil area.
TM = 0.008 x n x CM
where
| TM |
= |
max. tension, lb. |
| n |
= |
number of conductors |
| CM |
= |
cir-mil area of each conductor |
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- With cable grip over a lead sheath, the maximum pulling
tension in pounds should not exceed 1500 lb./sq. inch of lead sheath cross-sectional area
for commercial lead
TM = 1412t (D - t)
where
| t |
= |
sheath thickness, inches |
| D |
= |
overall diameter of cable, inches |
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- With cable grip over a non-leaded cable, the maximum pulling
tension should not exceed 1000 lbs. and may not exceed the maximum tension based on 0.008
or 0.006 x Total Conductor Area.
- When more than three conductors are pulled together, reduce
the pulling tension 20%.
B. Maximum Permissible Pulling Length
LM = 
where
| LM |
= |
pulling length, feet (straight section) |
| TM |
= |
maximum tension, lb. |
| W |
= |
weight of cable per foot, lb. |
| C |
= |
coefficient of friction (usually 0.5) |
C. Pulling Tension Requirements in Ducts or Conduits
- For straight sections, the pulling tension in pounds equals
the length of duct multiplied by the weight per foot of cable and the coefficient of
friction (paragraph B, above).
- For curved sections, the following formula applies:
 |
| where |
| T2 |
= |
tension for straight section at pulling end, lb. |
| T1 |
= |
tension for straight section at feeding end, lb. |
| TT |
= |
total tension |
| a |
= |
angle of bend in radians (1 rad = 57.3 degrees) |
| F |
= |
coefficient of friction (usually 0.5) |
| efa |
= |
 |
| e |
= |
Naperian logarithm base = 2.718 |
- (3) The maximum pulling tension in pounds shall not exceed
300 times the radius of curvature of the duct expressed in feet.
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