Planning the electrical installation
53
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 General rules
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 or copper wire. The better and tighter the shield, the lower the emission level
and 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
Separate parts of a conduit must be coupled together, bridge the joints with a ground
conductor bonded to the conduit on each side of the joint. Bond the conduits also to
the drive enclosure and motor frame. Use separate conduits for input power, motor,
brake resistor, and control wiring. When conduit is employed, type MC continuous
corrugated aluminium 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
Six 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, LAPPKABEL (ÖLFLEX) and
Pirelli.
Insulation jacket
Copper wire screen
Helix of copper tape
or copper wire
Cable core
Inner insulation
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