Planning the electrical installation 57
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 section General rules
above, or IEC 61439-1.
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.
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, 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
Six-conductor (three phases and three 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).
1 Sheath
2 Copper wire shield
3 Helix of copper tape or copper wire
4 Filling
5 Cable conductors
1
3 4 5
2
Sheath1
Copper wire shield2
Helix of copper tape or copper wire3
Filling4
Cable conductors5
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, 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
Six-conductor (three phases and three 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 the following suppliers:
• Belden
• LAPPKABEL (ÖLFLEX)
• Pirelli.
Selecting the control cables
￭ Shielding
All control cables must be shielded.
Use a double-shielded twisted pair cable (figure a below) for analog signals. Employ one
individually shielded pair for each signal. Do not use common return for different analog
signals.
A double-shielded cable is the best alternative for low-voltage digital signals but
single-shielded (b) twisted pair cable is also acceptable.
Planning the electrical installation 55
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