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Electrical Cable Bend Radius 1
- Thread starter crzymn711
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Per IEC 60092 "Electrical Installation on Ships", following is the recommended bending radius:
Upto 1kV - Cable Dia (D) ? 25.0 mm –Unarmored and unbraided cables = 4D
Armored and braided cables = 6D
Cable Dia (D) > 25.0 mm –Unarmored and unbraided cables = 6D
Armored and braided cables = 6D
Upto 1kV - Cable Dia (D) ? 25.0 mm –Unarmored and unbraided cables = 4D
Armored and braided cables = 6D
Cable Dia (D) > 25.0 mm –Unarmored and unbraided cables = 6D
Armored and braided cables = 6D
The cable manufacture will give the min bend rad for the cable in the cut sheets. This varies per cable type, insulation, and thickness. I'd use the manufactures spec. If ABS has a more stringent spec use that. Again you will need to know cable material, and gauge if it has one.
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The cable is being installed on military ships. The information I seek is to the history of the rationale used that developed the formula for the bend radius. What caused the need to go to this requirement, was it only the prevention of damage, and/or the result of previous fires or both?
Bend Radius requirements for a cable have multiple purposes. The obvious is to prevent damage during cable pulls (the tighter the radius the more side-wall pressure and more likely the insulation and jacket material are to be comprimised). In addition to that requirement, there is also a voltage withstand concern. Bends decrease an insulation systems service life in several ways:
Electrical energy will degrade the insulation through heat cycling and E-field stress (the electrical energy is trying to punch through the insulation, and on the outside of a bend the insulation inherently becomes thinner).
Outside portions of a bend have more chance of tearing, cutting, or simply stretching thin, further reducing the cable's jacket and insulation ability to resist other possible sources of failure (mechanical already mentione), but also chemical attack from gases in the air, even ozone generated by electric equipment, UV rays from types of lighting or the sun, and moisture.
It is not unlikely that a 600V up to 69kV cable will last only 20 years at the point of a bend while the straight sections would last as much as 55 years in the same operating environment.
This isn't even considering other issues such as increased conductor to shield capacitance due to thinner "dielectric" between them due to stretching, which can cause additional losses at that point, which translate to higher e-field, which translate to shorter insulation life. In MV cable, electrical and water treeing are predominant causes of cable failure often within 20 yrs of start of service. 90% of the time, cables fail at the point of termination. 9% of the time they fail at bends. 1% of the time, they fail elsewhere, and it's often due to damage during the installation (ie, being pulled too hard, especially around tight bends).
Exceeding recommended bend radius not only voids most warranties, but it also increases the chance of premature cable failure. Also, likelihood of failure goes up exponentially with each incrementally tighter bend. This is especially true with flex cables.
Having said all this, does that mean you can't exceed the bend radius? No, you can, but consult the Mfg of the cable and get a feeling of what they realistically think will work. Some cables are overdesigned enough that there is a significant margin for error.
Good luck!
Electrical energy will degrade the insulation through heat cycling and E-field stress (the electrical energy is trying to punch through the insulation, and on the outside of a bend the insulation inherently becomes thinner).
Outside portions of a bend have more chance of tearing, cutting, or simply stretching thin, further reducing the cable's jacket and insulation ability to resist other possible sources of failure (mechanical already mentione), but also chemical attack from gases in the air, even ozone generated by electric equipment, UV rays from types of lighting or the sun, and moisture.
It is not unlikely that a 600V up to 69kV cable will last only 20 years at the point of a bend while the straight sections would last as much as 55 years in the same operating environment.
This isn't even considering other issues such as increased conductor to shield capacitance due to thinner "dielectric" between them due to stretching, which can cause additional losses at that point, which translate to higher e-field, which translate to shorter insulation life. In MV cable, electrical and water treeing are predominant causes of cable failure often within 20 yrs of start of service. 90% of the time, cables fail at the point of termination. 9% of the time they fail at bends. 1% of the time, they fail elsewhere, and it's often due to damage during the installation (ie, being pulled too hard, especially around tight bends).
Exceeding recommended bend radius not only voids most warranties, but it also increases the chance of premature cable failure. Also, likelihood of failure goes up exponentially with each incrementally tighter bend. This is especially true with flex cables.
Having said all this, does that mean you can't exceed the bend radius? No, you can, but consult the Mfg of the cable and get a feeling of what they realistically think will work. Some cables are overdesigned enough that there is a significant margin for error.
Good luck!
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