Very long control cables and analog signals may, in rare cases and depending on installation, result in 50/60 Hz earth loops due to noise from mains
supply cables.
If this occurs, break the screen or insert a 100 nF capacitor between screen and chassis.
NB!
The common of digital / analog inputs and outputs should be connected to separate common terminals 20, 39, and 55. This will avoid
ground current interference among groups. For example, it avoids switching on digital inputs disturbing analog inputs.
NB!
Control cables must be screened/armoured.
5.2.3 Motor Cables
See section
General Specifications
for maximum 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 de-coupling plate of the frequency converter 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
frequency converter.
•
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.
F frame Requirements
F1/F3 requirements:
Motor phase cable quantities must be multiples of 2, resulting in 2, 4, 6, or 8 (1 cable is not allowed) to obtain equal amount of
wires attached to both inverter module terminals. The cables are required to be equal length within 10% between the inverter module terminals and the
first common point of a phase. The recommended common point is the motor terminals.
F2/F4 requirements:
Motor phase cable quantities must be multiples of 3, resulting in 3, 6, 9, or 12 (1 or 2 cables are not allowed) to obtain equal
amount of wires attached to each inverter module terminal. The wires are required to be equal length within 10% between the inverter module terminals
and the first common point of a phase. The recommended common point is the motor terminals.
Output junction box requirements:
The length, minimum 2.5 meters, and quantity of cables must be equal from each inverter module to the common
terminal in the junction box.
NB!
If a retrofit application requires unequal amount of wires per phase, please consult the factory for requirements and documentation
or use the top/bottom entry side cabinet busbar option.
5.2.4 Electrical Installation of Motor Cables
Screening of cables
Avoid installation with twisted screen ends (pigtails). They spoil the screening effect at higher frequencies.
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 increase, and the cable length must be reduced correspondingly.
5 How to Install
VLT
®
HVAC Drive Design Guide
90
MG.11.B9.02 - VLT
®
is a registered Danfoss trademark
5