1-4 General Installation Information
Unshielded Cable
THHN, THWN or similar wire is acceptable for drive installation in dry
environments provided adequate free air space and/or conduit fill rates
limits are provided. Do not use THHN or similarly coated wire in wet
areas. Any wire chosen must have a minimum insulation thickness of 15
Mils and should not have large variations in insulation concentricity.
Shielded Cable
Shielded cable contains all of the general benefits of multi-conductor cable
with the added benefit of a copper braided shield that can contain much of
the noise generated by a typical AC Drive. Strong consideration for shielded
cable should be given in installations with sensitive equipment such as
weigh scales, capacitive proximity switches and other devices that may be
affected by electrical noise in the distribution system. Applications with
large numbers of drives in a similar location, imposed EMC regulations or a
high degree of communications/ networking are also good candidates for
shielded cable.
Shielded cable may also help reduce shaft voltage and induced bearing
currents for some applications. In addition, the increased impedance of
shielded cable may help extend the distance that the motor can be located
from the drive without the addition of motor protective devices such as
terminator networks. Refer to Chapter 5, “Reflected Wave” in Wiring and
Grounding Guidelines for PWM AC Drives, publication DRIVES-IN001.
Consideration should be given to all of the general specifications dictated by
the environment of the installation, including temperature, flexibility,
moisture characteristics and chemical resistance. In addition, a braided
shield should be included and be specified by the cable manufacturer as
having coverage of at least 75%. An additional foil shield can greatly
improve noise containment.
A good example of recommended cable is Belden® 295xx (xx determines
gauge). This cable has four (4) XLPE insulated conductors with a 100%
coverage foil and an 85% coverage copper braided shield (with drain wire)
surrounded by a PVC jacket.
Other types of shielded cable are available, but the selection of these types
may limit the allowable cable length. Particularly, some of the newer cables
twist 4 conductors of THHN wire and wrap them tightly with a foil shield.
This construction can greatly increase the cable charging current required
and reduce the overall drive performance. Unless specified in the individual
distance tables as tested with the drive, these cables are not recommended
and their performance against the lead length limits supplied is not known.
Armored Cable
Cable with continuous aluminum armor is often recommended in drive
system applications or specific industries. It offers most of the advantages
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