Motor Cable Shield; Protecting The Relay Output Contacts And Attenuating Disturbances In Case Of Inductive Loads - ABB ACS850-04 Hardware Manual

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Motor cable shield

If the motor cable shield is used as the sole protective earth conductor of the motor,
ensure that the conductivity of the shield is sufficient. See section
above, or IEC 61439-1. 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 outputs on the drive are 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
General rules
Cable core