Points to Consider When Specifying
High-Performance Cables
Shielding: Shielding provides signal protection
against radiated electrical noise. Flexible cables
require specific flex shielding to accommodate the
stresses of motion. Alpha Wire’s SupraShield® uses
both foil and braid shields to provide exceptional
shielding at both low and high frequencies.
Flexible vs. Flexing: Flexible refers to the ability of
cable to be bent to make installation and routing easier.
Flexing refers to the ability of a cable to withstand
movement allowing cables to be used in motion control
applications requiring millions of flex cycles.
Chemicals, Oils, Solvents, and Fuels: Cables must
be evaluated for their ability to tolerate exposure
to contaminants, including their severity and the
likelihood of exposure. Such resistance is primarily a
function of insulation and jacketing materials.
Temperature: Engineers will plan for the electronic/
electrical characteristics needed in extreme
temperatures, but may forget to “hazard-match”
their choice of cable to accommodate the additional
physical demands.
　

What is a VFD Cable?
Variable-frequency drives (VFD) allow sophisticated
control by AC motors by allowing their speed and
torque to be precisely adjusted. Drives use pulsewidth
modulation (PWM) to achieve same power
profile as a sine-wave frequency.
　

How Can PWM Affect the VFD Cable?
Several phenomena can affect power, create noise,
reduce life of the cable, and disrupt operation of the
drive system.
Standing Waves: Impedance mismatches in the
signal path causes signal energy to reflect backwards.
Reflected waves can re-reflect, cause the noise
to “stand” on the line. The impedance difference
between motors/drives and cables can be significant,
with the resulting increase in voltage degrading the
cable’s insulation and leading to eventual failure.
Corona Discharge: Discharges harm the cable by
degrading the insulation material and damaging
the cable’s shield. A corona discharge can generate
enough heat to melt the conductor’s insulation.
Thermosetting insulations such as cross-linked
polyethylene provide much better resistance to
corona discharges than PVC.                                                                                                                                                                             Harmonic Distortion: All signals contain energy at
multiples of its frequency, in additions to energy at
its operating frequency. These signals result in wave
distortion due to a generation of harmonic energy.
In-Rush Current: When the motor is first started it
can draw very high current levels. Large VFD systems
can actually affect the power grid when they turn on.
EMI: Cables can emit or receive electromagnetic
energy as noise. This unwanted transfer of energy
to other circuits causes signal degradation, false
triggering, and other problems.

Points to Consider When Picking a
VFD Cable
Insulation: The cable must have excellent dielectric
properties to prevent breakdown from stresses of
voltage and current spike, corona discharges, and
so forth. The properties of cross-linked polyethylene
(XLPE) makes it a better choice than standard
polyethylene or PVC.
Shielding: Serves the double purpose of keeping
noise generated by the VFD cable from escaping,
and preventing noise generated outside the system
from being picked up.
Cable Geometry: A round symmetrical cable gives
the best electrical performance and resistance to
deleterious effects.

Flexing Cables
In selecting a cable for motion control, consider
not only the number of flex cycles but the type of
flexing. Cables are designed to withstand specific
types of flexing.
Rolling Flex: A continual back and forth
movement such as found in C-track or single-axis
Cartesian motion
Bending Flex or “tic-toc”: A back and forth
movement similar to a clock pendulum
Torsional Flex: A multiaxis movement that can
include twisting. A multiaxis articulated robot is
an example
Variable/Random Motion Flex: Irregular movement
with no defined regular path
For