Reeling Cable
Technical Manual

Anhui FeiChun Special Cable Co., Ltd., located in Hefei, Anhui Province, China, is a manufacturer specialising in the research and production of special industrial cables. Our products are widely used in port machinery, lifting equipment, mining, metallurgy, wind and solar power, rail transit and heavy industry.

The FeiChun range covers reeling cables, drag-chain cables, crane and port cables, low- and medium-voltage power cables, mining cables and rare-earth aluminium-alloy cables, supported by technical documentation and customised solutions for international markets, including Russia and the EAEU, Vietnam and Southeast Asia, Latin America, Australia and the Middle East.

The bending radius is the single most important factor in reeling-cable reliability. Too tight a radius induces stretching and internal torsion in the conductors, accelerating fatigue and breakage. An increase in the minimum bending radius has a more than proportional effect on cable life. The table below gives the recommended minimum bending radii for different uses, expressed as multiples of the cable overall diameter (OD).

One-way vs two-way: a one-way guide is often used on two-direction pay-out because it appears the most economical solution. However, a considerable increase in cable life is obtained with a symmetrical two-way guide, because it balances the net torsional and “massaging” effects imparted to the cable. This problem does not arise where the reeling system is end-fed: in that case the one-directional guide stays in contact with the cable regardless of travel direction.

Among the various guide types, the radius type is the best — it provides generous bending radii with minimum cable deflection. Multi-roller or two-way guides should be designed so the arc continues beyond the angle of deflection, keeping the minimum radius. A mandatory recommendation: keep the guide exactly aligned with the cable pay-out plane; any misalignment increases torsion on the cable.

Change of direction: at the design stage, leave enough distance between any changes of direction — at least 20 × cable OD (longer for high-speed systems). This allows the cable to regain its original shape before suffering another bend.

It is highly recommended that cable guiding systems include both under- and over-tension protection. Even a short exposure to over-tension caused by mechanical failure or accident can render a cable inoperable through permanent conductor deformation or breakage. All over-tension devices should be set to the maximum continuous safe working tension defined for each cable section.

Conversely, under-tension protection is desirable to ensure the cable cannot free-spool from the reel and sustain damage. This protection is particularly important for high-mounted cable reels.

Correct cable anchoring is fundamental to reliable operation. Different handling systems use different methods, but all share the same basic intent: spread the tensile forces over a sufficiently large sheath area to avoid damage or failure at the anchoring point.

Cable life and performance are tightly connected to the reeling design. A well-designed reeling system, combined with the correct cable choice, secures optimal performance and long cable life. Today’s reels fall into three main types:

For optimum long-life service, laying must be carried out by expert personnel. In addition to the normal measures for laying cables, the operating conditions specific to mobile cables require the points below to be strictly observed. Test the installation a few times as soon as the cable has been laid, to check operation and immediately correct any defect.

If the cable has become twisted during the above procedure, we strongly recommend eliminating it. There is an important physical law: a correctly installed cable, with no torsion introduced by guides or unnatural bending, cannot twist by itself. Two methods are normally used.

Anchoring: installation on a spreader or other vertical application needs special attention. The earlier recommendations (wind from the original drum; avoid unnecessary loops, torsion or twisting; eliminate any torsion) apply here too. The best anchoring is achieved with a stress-relief drum: its open-ended construction eases installation and replacement and gives better stress relief and sheath protection than cable grips — in this case at least 2 turns should be wound. If a grip is used, the recommended coverage is 20/25 × OD.

Fixing the bottom: where necessary, fix the bottom with a suitable grip; sheath coverage is the same as the anchoring (20/25 × OD). The distance from the end of the anchoring device to the end of machine travel should be at least 40 × OD. If frequent dynamic stresses near the anchor are anticipated, a spring may be used.

Rated voltage is the basis for the design and testing of the cable’s electrical characteristics, expressed by the two power-frequency values U₀/U: U₀ is the rms value between one conductor and earth, U the rms value between two conductors. In an AC system, the cable’s rated voltage must be at least equal to the system rated voltage — for both U₀ and U. In a DC system, its rated voltage must not be more than 1.5 times the cable’s rated value.

Operating voltage is the voltage applied between conductors and earth in trouble-free operation. For cables up to U₀/U 0.6/1 kV, the maximum continuous operating voltage must not exceed the rated value by more than +10 % (up to 450/750 V) or +20 % (0.6/1 kV). For cables above 0.6/1 kV, by no more than +20 %. Test voltage follows the relevant parts of DIN VDE 0250; voltage definitions follow DIN VDE 0298 Part 3.

The current ratings and derating factors below are based on DIN VDE 0298-4. Although mobile cables are often EPR/rubber insulated (continuous 90 °C permissible), the ratings here are given for a conductor temperature of 80 °C — both to conform to VDE and as a precaution for the greater heat-dispersion difficulty of this cable type. Values are for three-core cables (with or without earth), not wound, resting on the ground, ambient air 30 °C. Where the cable life is known to be reduced by high mechanical stress or sheath wear, thermal ageing is less important, and 90 °C may be considered, increasing the values by approximately 7 %.

Derating factors take into account installation and operating conditions (temperature, grouping, intermittent periodic duty, number of simultaneously loaded cores) and are used together with the ratings above.

In many cases operation is not continuous. A typical intermittent cycle with hoisting equipment is, for example, 10 minutes of full load followed by a longer no-load period. These 10 minutes as a percentage of the total cycle DT give the load factor FC %. For intermittent duty the current rating can be increased accordingly.

Voltage drop should be checked not only for low voltage but also for medium-voltage connections where lengths are long. It is found by multiplying the cable factor K (mV/A·m) by the current and the line length.

In accordance with VDE 0250, the admissible thermal limit for short-circuit current in heavy-duty mobile cables is calculated from these reference values: initial temperature 80 °C (cable under full load), final short-circuit temperature 200 °C. The table gives the one-second thermal limit. For other periods, divide by the square root of the effective time in seconds.