NotesWiring method
Free air
2)
Prefer symmetrical shielded VFD cable.
Enclosures, air handlers, etc. Allowed internally in enclosures when in accord-
ance with UL.
1)
Metallic conduit may be used as an additional ground path, provided this path is a solid path capable of
handling ground currents.
2)
See NFPA NEC 70, UL, and local codes for your application.
3)
Non-metallic conduit use underground is allowed; however, these installations inherently have an increased
chance for nuisance problems due to the potential for water/moisture in the conduit. Water/moisture in the
conduit increases the likelihood of VFD faults or warnings. Proper installation is required to make sure there
is no intrusion of water/moisture.
Metal conduit
Couple separate parts of a metal 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. Do not run motor wiring from more than one drive in the
same conduit.
￭ Power cable shield
If the cable shield is used as the sole protective earth (PE) conductor, make sure that
its conductivity agrees with the PE conductor requirements.
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.
Insulation jacket1
Helix of copper tape or copper wire2
Copper wire shield3
Inner insulation4
Cable core5
74 Guidelines for planning the electrical installation
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