Motor Thermal Protection; Parallel Connection Of Motors - Danfoss FC 300 Design Manual

FC 300 Design Guide
• Terminal U/T1/96 connected to U-phase
• Terminal V/T2/97 connected to V-phase
• Terminal W/T3/98 connected to W-phase
The direction of rotation can be changed by switching two phases in the motor cable or by changing the setting of par. 4-10
Motor rotation check can be performed using par. 1-28
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 applications requires unequal amount of wires per phase please consult the factory for requirements and documentation
or use the top/bottom entry side cabinet option.

8.5.2 Motor Thermal Protection

The electronic thermal relay in the frequency converter has received UL-approval for single motor protection, when par. 1-90
tion is set for ETR Trip and par. 1-24
For thermal motor protection it is also possible to use the MCB 112 PTC Thermistor Card option. This card provides ATEX certificate to protect motors in
explosion hazardous areas, Zone 1/21 and Zone 2/22. Please refer to the

8.5.3 Parallel Connection of Motors

The frequency converter can control several parallel-connected motors.
When using parallel motor connection following must be observed:
• Recommended to run applications with parallel motors in U/F
mode par. 1-01 [0]. Set the U/F graph in par. 1-55 and 1-56.
• VCC+ mode may be used in some applications.
• The total current consumption of the motors must not exceed
the rated output current I
INV
• If motor sizes are widely different in winding resistance, starting
problems may arise due to too low motor voltage at low speed.
Motor Rotation Check
Motor Current is set to the rated motor current (see motor name plate).
for the frequency converter.
MG.33.BC.02 - VLT ® is a registered Danfoss trademark
and following the steps shown in the display.
Design Guide
for further information.
• The electronic thermal relay (ETR) of the frequency inverter
cannot be used as motor protection for the individual motor.
Provide further motor protection by e.g. thermistors in each
motor winding or individual thermal relays. (Circuit breakers are
not suitable as protection device).
NB!
Installations with cables connected in a common joint
as shown in the first example in the picture is only rec-
ommended for short cable lengths.
8 Electrical Installation
Motor Speed Direction .
8
Motor Thermal Protec-
175