Servo & feedback cables vs motor cables: How to tell them apart?

1.1 What are servo & feedback cables?

In the field of electrical engineering, the cable used to connect a servo drive to a servo motor is called a servo cable. This cable serves to transmit both power and control signals from the frequency converter to the motor. Unlike direct power supply, the frequency converter controls the motor speed by adjusting the shape of the voltage waveform.

For this reason, servo & feedback cables are typically rated at 600/1000V and are designed with an overall shielding to protect the signals and minimize electromagnetic interference (EMI) in industrial environments.

In addition to the main power cores, servo & feedback cables also include two additional shielded pairs for connecting temperature sensors or electromagnetic brake systems on the servo motor. This design allows the cable to deliver power while ensuring precise, safe, and stable control of the drive system.

>>Find out more: What are servo motors? Their features and applications

1.2 Construction of servo & feedback cables

One of the most important aspects of a servo & feedback cable is its shielding. Basically, servo & feedback cables feature two types of shielding:

• Overall shield: This layer surrounds all the cable cores and ensures electromagnetic compatibility (EMC). It prevents the voltage and signals within the cable from interfering with other devices, machine components, or nearby control systems.
• Shield for control pairs: These shielded pairs prevent noise from the power lines from affecting the control circuits, ensuring that the data transmitted to the frequency converter remains accurate and stable.

The design of the shielding varies depending on the mechanical stresses the servo cable must withstand, such as continuous bending, stretching, vibration, or harsh industrial environments. For high-performance applications, the shielding coverage can reach 85–90%, enhancing both EMI protection and mechanical durability.

Additionally, to support high-speed and stable signal transmission, the control pairs are usually twisted using a specialized technique. This not only improves electromagnetic shielding but also allows for faster installation and easier connections.

Thanks to this design, servo & feedback cables not only transmit power but also protect and maintain the precision of control signals, ensuring that servo motors operate reliably in modern automation systems.

1.3 Applications of servo & feedback cables

Thanks to their specialized structure with shielding and control signal cores, servo & feedback cables not only transmit electrical power but also ensure precise and stable control signals. For this reason, they are widely used in many modern industrial applications:

• Machine tools: Used in CNC machines, milling machines, lathes, and grinders with multiple moving axes.
• Industrial robots and automation: Employed in linear robots, pick-and-place robots, welding robots, and assembly robots.
• Packaging and production lines: In packaging, bottling, and labeling machines, servo cables enable precise speed and position control.
• Automotive industry: Applied in car assembly lines, painting systems, and automated welding stations.
• Other industries: Pharmaceutical and food processing, printing and packaging, and energy sectors, among others.

2.1 What are motor cables?

To supply power to a three-phase electric motor, a motor cable is used. Typically, this type of cable consists of:

• Three black cores corresponding to the three phases L1, L2, and L3.
• One green-yellow core serving as the Protective Earth (PE), ensuring safety and preventing electrical leakage.

In practice, the stator windings of the motor are usually connected in either a star (Y) or delta (Δ) configuration. This connection method reduces the number of cores needed in the cable to four, making it simpler and more cost-effective.

The outer sheath of a motor cable can be made from various materials such as PVC, PUR, or specialized rubber, depending on requirements for oil resistance, chemical resistance, abrasion resistance, or high-temperature tolerance.

2.2 Motor supply cables and motor control cables

A motor supply cable is a specialized electrical cable designed specifically to deliver power to motors. These heavy-duty cables are capable of carrying high voltages and currents while withstanding the demanding operating conditions that motors often encounter. The main function of a motor supply cable is to transmit electrical energy from a power source (such as a control cabinet or transformer) directly to the motor. With high reliability, this type of cable ensures stable and continuous power delivery, which is especially important in applications requiring motors to operate continuously, precisely, and efficiently.

In contrast, a motor control cable is responsible for transmitting control signals that direct the operation of the motor according to system requirements. These cables are specially designed to carry the electrical currents needed for motor control while providing mechanical protection and durability for long-term operation.

3.3 Cable color coding according to DESINA standard

One of the most noticeable differences between these two types of cables is their color. Typically, servo cables are pastel orange, while motor cables have a black jacket. This distinction comes from the DESINA standard, which is a mechanical engineering standard aimed at standardizing cable systems.

According to DESINA:

• Motor cables: must have a black outer jacket.
• Servo cables: must have a pastel orange outer jacket (RAL 2003).

DESINA stands for Distributed and Standardized Installation Technology for machine tools and manufacturing systems. It is a set of specifications that standardizes electrical, hydraulic, and pneumatic components, as well as their interconnections on a single platform for CNC-controlled machine tools and production systems.

Since November 2005, after the publication of ISO 23570 Parts 1 and 2 by the International Organization for Standardization (ISO), DESINA installation technology has been recognized as an international standard.

The color coding according to functional codes is as follows:

• Orange (RAL 2003): Servo applications, shielded
• Green (RAL 6018): Measuring systems, shielded
• Violet (RAL 4001): Fieldbus, shielded
• Yellow (RAL 1021): Sensors/actuators, not shielded
• Black (RAL 9005): Outputs, not shielded
• Gray (RAL 7040): 24 V control cables, not shielded

4.1 Servo & feedback cables

HELUKABEL offers servo & feedbacks cable series made from a variety of materials such as PVC, PUR, and TPE.

We offer various servo & feedback cables adhered to various standards such as UL/CSA, ECOLAB, VDE, UKCA...

4.2 TPE servo & feedback cables

TOPSERV® 600 VFD and TOPSERV® 650 VFD are our special servo cable products. These cables are made from premium TPE material, making them particularly suitable for applications in environments with extreme temperature ranges. Key features of these two products include:

• Stable operation in temperatures from -45°C to +105°C, suitable for both deep-freeze areas and high-temperature environments
• ECOLAB certified, ideal for the F&B industry
• Compliant with UL tray cable standards: UL 1277 and WTTC 2277
• Excellent mechanical properties, meeting UL Exposed Run (ER) standards: TC-ER, PLTC-ER, ITC-ER, allowing direct installation without conduit or protective trays

TC = Tray Cable, ITC = Instrumentation Tray Cable, PLTC = Power-Limited Tray cable

4.4 Single-core motor cables

In addition to the traditional four-core motor cables, HELUKABEL also offers single-core motor cables for high-power drive systems. This solution provides several advantages:

• Lower cost compared to multi-core alternatives.
• High durability, suitable for tight installation spaces in cable chains, while also offering a longer service life, especially in applications with long travel distances.

The TOPFLEX® 302 / 302-UL motor cables are highly flexible single-core cables, featuring double-layer PVC insulation and excellent low-temperature flexibility. The 302-UL version is UL Approval certified (Style 10107).

4.5 Hybrid servo motor cables

Hybrid cables are transforming the design of automation systems, especially in servo motor applications. Instead of using separate motor and feedback cables (encoder or resolver), hybrid cables integrate both functions into a single solution.

Using hybrid cables offers several clear advantages:

• Space efficiency: Frees up space inside the cable carrier and at the motor connection area.
• Cost savings: One cable replaces two, significantly reducing material and accessory costs.
• Enhanced reliability: Fewer connectors mean fewer potential failure points, improving system durability and stability.

HELUKABEL’s hybrid servo motor cable products are available in two versions:

• TOPSERV® Hybrid PVC : Suitable for fixed installations or applications with infrequent movement.
• TOPSERV® Hybrid PUR : Highly flexible, designed for drag chain applications.