Planning the electrical installation
74
Motor cable shield
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.
Additional US requirements
Type MC continuous corrugated aluminum armor cable with symmetrical grounds or
shielded power cable must be used for the motor cables if metallic conduit is not
used. For the North American market, 600 V AC cable is accepted for up to
500 V AC. 1000 V AC cable is required above 500 V AC (below 600 V AC). For
drives rated over 100 amperes, the power cables must be rated for 75
°C (167 °F).
Conduit
Where conduits must be coupled together, bridge the joint with a ground conductor
bonded to the conduit on each side of the joint. Bond the conduits also to the drive
enclosure. Use separate conduits for input power, motor, brake resistors, and control
wiring. When conduit is employed, type MC continuous corrugated aluminum armor
cable or shielded cable is not required. A dedicated ground cable is always required.
Note: Do not run motor wiring from more than one drive in the same conduit.
Armored cable / shielded power cable
6-conductor (3 phases and 3 ground) type MC continuous corrugated aluminum
armor cable with symmetrical grounds is available from the following suppliers (trade
names in parentheses):
• Anixter Wire & Cable (Philsheath)
• BICC General Corp (Philsheath)
• Rockbestos Co. (Gardex)
• Oaknite (CLX).
Shielded power cables are available from Belden, Lapp Kabel (ÖLFLEX) and Pirelli,
among others.
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