NB!
If a retrofit application requires unequal amount of wires per phase, please consult the factory for requirements.
5.3.6 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.
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
Switching Frequency
.
Aluminium conductors
Aluminium conductors are not recommended. Terminals can accept aluminium conductors but the conductor 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.
5.3.7 Fuses
NB!
All fuses mentioned are max. fuse sizes.
Branch circuit protection:
In order to protect the installation against electrical and fire hazard, all branch circuits in an installation, switch gear, machines etc., must be shortcircuit
and overcurrent protected according to the national/international regulations.
Short circuit protection:
The frequency converter must be protected against short-circuit to avoid electrical or fire hazard. Danfoss recommends using the fuses mentioned in
tables 5.3 and 5.4 to protect service personnel or other equipment in case of an internal failure in the unit. The frequency converter provides full short
circuit protection in case of a short-circuit on the motor output.
Over-current protection:
Provide overload protection to avoid fire hazard due to overheating of the cables in the installation. Over current protection must always be carried out
according to national regulations. The frequency converter is equipped with an internal over current protection that can be used for upstream overload
protection (UL-applications excluded). See par. 4-18. Fuses must be designed for protection in a circuit capable of supplying a maximum of 100,000
A
rms
(symmetrical), 500 V/600 V maximum.
Non UL compliance:
If UL/cUL is not to be complied with, Danfoss recommends using the fuses mentioned in table 5.2, which will ensure compliance with EN50178:
In case of malfunction, not following the recommendation may result in unnecessary damage to the frequency converter.
VLT
®
AQUA Drive Design Guide
5 How to Install
MG.20.N5.02 - VLT
®
is a registered Danfoss trademark
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