Motor Cables - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide

Motor Cables

See section General Specifications for correct dimensioning of motor cable cross-section and length.
• Use a screened/armoured motor cable to comply with EMC emission specifications.
• Keep the motor cable as short as possible to reduce the noise level and leakage currents.
• Connect the motor cable screen to both the decoupling plate of the FC 300 and to the metal
cabinet of the motor.
• Make the screen connections with the largest possible surface area (cable clamp). This is done
by using the supplied installation devices in the FC 300.
• Avoid mounting with twisted screen ends (pigtails), which will spoil high frequency screening
effects.
• If it is necessary to split the screen to install a motor isolator or motor relay, the screen must be
continued with the lowest possible HF impedance.
Electrical Installation of Motor Cables
Screening of cables
Avoid installation with twisted screen ends (pigtails). They spoil the screening effect at higher frequen-
cies.
If it is necessary to break the screen to install a motor isolator or motor contactor, the screen must be
continued at the lowest possible HF impedance.
Cable length and cross-section
The frequency converter 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 in-
crease, and the cable length must be reduced correspondingly.
Switching frequency
When frequency converters 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 instruction in Par. 14-01.
Aluminium conductors
Aluminium conductors are not recommended. Terminals can accept aluminium conductors but the con-
ductor surface has to be clean and the oxidation must be removed and 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 aluminium.
It is crucial to keep the connection a gas tight joint, otherwise the aluminium surface will oxidize again.
How to Install
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MG.33.B8.02 - VLT is a registered Danfoss trademark
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