Corrugated or EMT cable with three phase conductors and a protective
conductor is allowed for motor cabling with phase conductor cross
EMT
section less than 10 mm 2 (8 AWG) or motors ≤ 30 kW (40 hp).
Not allowed power cable types
Symmetrical shielded cable with individual shields for each phase con-
PE
ductor is not allowed on any cable size for input or motor cabling.
■
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 (page 68)
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.
1
Sheath
2
Copper wire shield
3
Helix of copper tape or copper wire
4
Filling
5
Cable conductors
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
above, or IEC 61439-1.
1
Planning the electrical installation 71
3
4
2
5