SPEC E100
January, 2008
Installation—Training and Bending Limitations
Physical Limitations Training and Bending Overview Training is the positioning of cable when it is not under tension. Bending is the positioning of cable when it is under tension. When installing cable, the object is to limit the mechanical forces so that the cable’s physical and electrical characteristics are maintained for the expected service life. Bends in conductors, multiconductor cables or assemblies of conductors shall be made so that the cable will not be damaged.
The problem is compounded by the fact that most tapes are under jackets that sconceal such damage. The extruded polymers used for insulation shields have sufficient conductivity and coverage initially to pass acceptance testing, then fail prematurely due to corona at the shield/insulation interface.
A nonshielded cable can tolerate a sharper bend than a shielded cable. This is especially true for cables having helically applied metallic shielding tapes which, when bent too sharply, can separate or buckle and cut into the insulation. Remember that offsets are bends.
Minimum Bending Radius in Accordance with National Electric Code Voltage Conductors Shielding Cable Types 600V 6012000V
Single
Nonshielded
All
5X
All
8X
Nonshielded TC or TC-ER
600V Multiconductor or or Multiplexed 2000V
Over 2000V
Multiconductor Multiplexed
1 in. (25 mm) or less 4X
Shielded
Single
Minimum Bending Radius as a Multiple of Conductor/Assembly Diameter
Nonshielded
Over 1 in. to 2 in. (>25 mm to 50 mm)
Over 2 in. (>50 mm)
5X
6X
MC3
7X
All
12X
TC or TC-ER
12X
MC
12X/7X1
MV MC
3
Shielded
MC and MV
Nonshielded
MC and MV
Shielded
MC and MV
8X 7X 12X
2
8X 1,2
12X/7X
1
12 times the diameter of an individual shielded conductor or 7 times the overall cable diameter, whichever is greater. Since UniShield® is a unique construction, there are no applicable values for the bending radius in the NEC. However, General Cable recommends 8 times for single conductors, and for multiplexed or multi-conductor cables, it is 8 times the diameter of the individual conductors or 5 times the overall diameter, whichever is greater, in accordance with ANSI/ICEA S-93-639 5-46kV Shielded Power Cable for Use in the Transmission and Distribution of Electric Energy. 3 Per 330.24B Interlocked-Type Armor or Corrugated Sheath. 2
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