Motor Cable Shield; Protecting The Relay Output Contacts And Attenuating Disturbances In Case Of Inductive Loads - ABB ACSM1 Hardware Manual

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Motor cable shield

To function as a protective conductor, the shield must have the same cross-sectional
area as a phase conductor when they are made of the same metal.
To effectively suppress radiated and conducted radio-frequency emissions, the
shield conductivity must be at least 1/10 of the phase conductor conductivity. The
requirements are easily met with a copper or aluminium shield. The minimum
requirement of the motor cable shield of the drive is shown below. It consists of a
concentric layer of copper wires with an open helix of copper tape. The better and
tighter the shield, the lower the emission level and the bearing currents.
Protecting the relay output contacts and attenuating disturbances in case
of inductive loads
Inductive loads (relays, contactors, motors) cause voltage transients when switched
off.
The relay output on the drive is protected with varistors (250 V) against overvoltage
peaks. In addition, it is highly recommended to equip inductive loads with noise
attenuating circuits (varistors, RC filters [AC] or diodes [DC]) in order to minimize the
electromagnetic emissions at switch-off. If not suppressed, the disturbances may
connect capacitively or inductively to other conductors in the control cable and form
a risk of malfunction in other parts of the system.
Planning the electrical installation
Copper wire screen
Insulation jacket
Inner insulation
Helix of copper tape
Cable core