Selecting Cables for Stepper or Servo System

Selecting appropriate cables for your motion control system is essential to achieving and maintaining desired performance. Poor cable selection deprives systems of efficiency and reliability.

Key Factors in Cable Selection

Before cable can be chosen, the engineer must understand the operating environment. Variables like temperature, moisture, and hazards should be taken into account. Some rules of thumb:

• Insulation: Appropriate type and thickness of insulation depend on working voltages.
• Conductors & Current: These will be specified by the motor and drive manufacturer.
• Shielding: Higher grades of shielding are required if EM interference will be a factor.
• Turns Per Inch: Up to four turns per inch may be used to curb likelihood of coupling.

Cable flexibility is also essential. Shielding and insulation can reduce flexibility, so begin with the intended application in mind. In general, a limited movement range demands less flexibility.

Engineers should be sure desired cables meet any relevant regulatory standards. Some environments require flame retardant cabling elements or limit total conductors per conduit.

An Overview of Cable Components

Though a cable may seem simple, it is a complex and precise component with many interdependent parts. All engineers should be familiar with the different elements inside each length of cable.

Insulation and Jacket

The jacket is the outer “skin” of the cable that protects it from the environment. By contrast, the conductor insulation helps to isolate individual pairs of wires in the cable and prevent cross-talk.

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Termination

Proper termination is essential to a cable’s basic function. While different motor manufacturers produce or suggest different connectors, straight and right angle varieties are the most common.

Conductors

Any cable might consist of a single conductor or pairs of multiple insulated conductors that carry current for control and power circuits simultaneously. Copper is the most common conductor.

Shielding

Shielding can be applied over the individual conductors, the pairs, or the entire cable. Typically, a jacket covers the entire shield. Shielding and wire twists work together to reduce interference.

Connectors

Each connector inevitably leads to some performance degradation. In general, the total number of connections for a cable run should be minimized and the type of connector chosen carefully.

High Flex & Continuous Flex

High-flex cables are essential for any applications where the motor or feedback device must move frequently relative to the controller. To improve cable life, minimize the bend radius.

It's easy to overlook cabling, but optimum cable selection can enhance system performance!