A cable can feel flexible in your hand and still be the wrong cable for a moving machine.
This is one of the most common misunderstandings when choosing cables for CNC machines, automation equipment and drag chain systems.
Standard flexible cables and high-flex drag chain cables may look similar from the outside, but they are designed for very different working conditions.
The easiest way to choose between them is to look at one thing first:
Does the cable keep moving while the machine is running?
If it does, flexibility alone is not enough.
Standard flexible cables such as RVV and RVVP use stranded copper conductors and are easy to route during machine assembly.
They work well for control cabinets, equipment wiring and other applications where the cable remains mostly stationary after installation.
The cable may be bent during installation or maintenance, but it is not normally selected for millions of repeated bending movements.
That is the important difference.
A cable being soft does not mean it is designed for continuous movement inside a drag chain.
A drag chain cable works under a completely different condition.
When a CNC axis or automated machine moves, the cable travels with the drag chain. One operating cycle may not seem demanding, but after months or years of operation, the cable can experience millions of bending movements.
This is why the conductor, core arrangement, shielding and outer jacket all need to be designed around movement.
For example, our TRVVP high-flex shielded drag chain cable is available in versions designed for different bending-cycle requirements, including 6 million, 10 million, 15 million and 30 million cycles.
For more demanding applications, our 30-million-cycle TRVVP uses an ultra-fine stranded conductor with an approximate strand diameter of 0.08 mm. It also uses aluminum foil plus tinned-copper braid shielding with ≥92% shield coverage and a PUR outer jacket.
Under the specified installation conditions, this version is designed for more than 30 million bending cycles, with unsupported travel speeds up to 3 m/s.
These figures are useful because “high-flex” by itself does not tell you enough about how a cable will perform in a moving system.
| Item | Standard Flexible Cable | High-Flex Drag Chain Cable |
|---|---|---|
| Main use | Fixed or occasional movement | Continuous reciprocating movement |
| Typical cable | RVV / RVVP / RVVPS | TRVV / TRVVP / TRVVPS |
| Conductor | Flexible stranded copper | Fine or ultra-fine stranded copper |
| Bending cycles | Not normally specified for continuous drag-chain use | Can be specified by series |
| Example bending life | — | 6M / 10M / 15M / 30M cycles |
| Installation | Machine wiring, control cabinet | Drag chain / moving axis |
| Shielded option | Yes | Yes |
| Typical equipment | General industrial equipment | CNC, robots, automation equipment |
The exact specification depends on the selected cable construction and operating conditions.
This is another question we often receive.
More bending cycles do not automatically mean that every machine should use the highest-cycle cable.
For example, our 6-million-cycle TRVVPS is designed for continuous-flex applications and uses twisted pairs for signal transmission. It is suitable for applications such as servo feedback, encoders, sensors and automated equipment.
Its conductor uses fine-stranded oxygen-free copper, with PVC insulation and a flexible PVC outer sheath.
The 30-million-cycle TRVVP, on the other hand, is intended for more demanding continuous-motion applications. It uses an approximately 0.08 mm ultra-fine stranded conductor, dual shielding and a polyether PUR jacket.
So the selection should depend on the machine, not simply the biggest number on the cable.
It may work.
At least at the beginning.
This is why the problem is sometimes difficult to notice during machine commissioning.
After repeated movement, however, a cable that was not designed for continuous flexing can develop conductor fatigue, jacket damage or unstable electrical connections.
In signal applications, you may notice intermittent feedback or signal problems before the cable completely fails.
The outside of the cable can even look normal while the conductors inside have already been damaged.
For an automated production line, this can turn a relatively inexpensive cable into an expensive maintenance problem.
If shielding is required, the internal cable structure also matters.
TRVVP uses a general multi-core arrangement and is suitable for shielded control, signal and power applications in moving equipment.
TRVVPS uses twisted pairs together with overall shielding.
The twisted-pair structure is particularly useful for low-voltage signal and feedback circuits, where reducing crosstalk and external electromagnetic interference is important.
Typical applications include:
Servo feedback
Encoders
Resolvers
Industrial sensors
CNC machines
Automated production equipment
So when a customer asks us for a “shielded drag chain cable,” we still need to know what signal or power the cable will carry.
The working environment also affects cable selection.
PVC drag chain cables are a practical choice for many general industrial automation applications.
For applications involving more demanding mechanical conditions, abrasion or oil exposure, PUR is often a better option.
For example, our 30-million-cycle TRVVP uses a polyether-based PUR jacket designed for resistance to oil, abrasion and repeated mechanical stress.
Again, this doesn't mean PUR is necessary for every application. The cable should match the actual environment.
Instead of starting with the cable model, start with the machine.
If the cable remains stationary after installation, a standard flexible cable is normally enough.
If it moves continuously inside a drag chain, choose a cable designed and tested for continuous-flex operation.
Then look at the actual working conditions:
Bending cycles:
How often does the machine move?
Bending radius:
How tightly does the cable bend inside the drag chain?
Travel distance:
How far does the moving axis travel?
Speed and acceleration:
A slow-moving machine and a high-speed CNC axis place different mechanical loads on the cable.
Signal or power:
Power, control, encoder and sensor circuits may require different cable structures.
Working environment:
Check for oil, abrasion, temperature and other environmental conditions.
When comparing high-flex cables, don't look only at “6 million” or “30 million.”
Bending-cycle life is related to the test and installation conditions.
Cable diameter, bending radius, travel speed, acceleration, drag chain installation and operating environment can all affect actual service life.
For this reason, our bending-cycle figures are specified under defined test or installation conditions rather than treated as a guarantee for every machine.
For final cable selection, the actual motion data should always be checked.
Fixed installation / occasional movement
→ Standard flexible cable such as RVV or RVVP
General continuous drag-chain movement
→ TRVV / TRVVP series
Signal or feedback circuits requiring twisted pairs and shielding
→ TRVVPS
Higher cycle requirements or more demanding moving conditions
→ Select the appropriate 10M, 15M or 30M high-flex series according to the application
Oil, abrasion or demanding industrial environment
→ Consider a PUR-jacket high-flex cable
There is no need to use the highest-specification cable for every machine.
The right cable is the one that matches the movement, electrical requirements and working environment.
If you are not sure which cable to use, send Rolan Cable your cable size, number of cores, application, bending radius, travel distance, speed and working environment. We can help you compare the available constructions and select a suitable cable for your equipment.
