66 Guidelines for planning the electrical installation
Motor cable shield
If the motor cable shield is used as the sole protective earth conductor of the motor, make
sure that the conductivity of the shield is sufficient. See subsection General rules above, or
EC 61800-5-1. To effectively suppress radiated and conducted radio-frequency emissions,
the cable shield conductivity must be at least 1/10 of the phase conductor conductivity.
The requirements are easily met with a copper or aluminum 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
Use type MC continuous corrugated aluminum armor cable with symmetrical grounds or
shielded power cable 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
Couple separate parts of a conduit together: bridge the joints with a ground conductor
bonded to the conduit on each side of the joint. Also bond the conduits 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 aluminum
armor cable or shielded cable is not required. A dedicated ground cable is always
required.
Note: Do not install 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.
1 Insulation jacket
2 Helix of copper tape or copper wire
3 Copper wire screen
4 Inner insulation
5 Cable core
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