4.1.9. How to connect the motor - foreword
See section
General Specifications
for correct dimensioning of motor cable cross-section and
length.
• Use a shielded/armored motor cable to comply with EMC emission specifications (or in-
stall the cable in a metal conduit).
• Keep the motor cable as short as possible to reduce the noise level and leakage currents.
• Connect the motor cable shield/armor to both the decoupling plate of the adjustable
frequency drive and to the metal of the motor. (Same applies to both ends of the metal
conduit if used instead of a shield.)
• Make the shield connections with the largest possible surface area (by using a cable
clamp or an EMC cable gland). This is done by using the supplied installation devices in
the adjustable frequency drive.
• Avoid terminating the shield by twisting the ends (pigtails), as this will spoil high fre-
quency shielding effects.
• If it is necessary to break the continuity of the shield to install a motor isolator or motor
relay, the continuity must be maintained with the lowest possible HF impedance.
Cable length and cross-section
The adjustable frequency drive has been tested with a given length of cable and a given cross-
section of that cable. If the cross-section is increased, the cable capacitance - and thus the leakage
current - may increase, thereby requiring that the cable length is reduced accordingly.
Switching frequency
When adjustable frequency drives are used together with sine wave filters to reduce the acoustic
noise from a motor, the switching frequency must be set according to the sine wave filter in-
structions in
Par. 14-01
.
Precautions while using Aluminum conductors
Aluminum conductors are not recommended for cable cross-sections less than 0.054 in² [35
mm²]. Terminals can accept aluminum conductors, but the conductor surface has to be clean,
oxidation must be removed, and the area must be sealed by neutral acid-free Vaseline grease
before the conductor is connected.
Furthermore, the terminal screw must be retightened after two days due to the softness of the
aluminum. It is crucial to ensure the connection makes a gas tight joint, otherwise the aluminum
surface will oxidize again.
VLT
®
HVAC Drive Instruction Manual 4. Electrical installation
MG.11.A4.22 - VLT
®
is a registered Danfoss trademark
35
4
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