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

8 Electrical Installation
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 8.2 ft [2.5 m], and quantity of cables must be equal from each inverter module to the
common terminal in the junction box.
NOTE!
If a retrofit application requires unequal amounts 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 adjustable frequency drive has received UL approval for single motor protection, when par. 1-90
Protection is set for ETR Trip
For thermal motor protection, it is also possible to use the MCB 112 PTC thermistor card option. This card provides an ATEX certificate to protect motors
in explosion hazard areas, Zone 1/21 and Zone 2/22. Please refer to the
8

8.5.3 Parallel Connection of Motors

The adjustable frequency drive can control several parallel-connected
motors. When using a parallel motor connection, the following must be
observed:
• It is 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
• If motor sizes are widely different in winding resistance, starting
problems may arise due to too low motor voltage at low speed.
• The electronic thermal relay (ETR) of the frequency inverter
cannot be used as motor protection for the individual motor.
Provide further motor protection, e.g., by thermistors in each
motor winding or individual thermal relays. (Circuit breakers are
not suitable as protection devices).
NOTE!
Installations with cables connected using a common
joint, as shown in the first example in the picture, are
only recommended for short cable lengths.
8-30
and par. 1-24 Motor Current is set to the rated motor current (see motor nameplate).
for the adjustable frequency drive.
INV
MG.33.BC.22 - VLT
Design Guide
for further information.
NOTE!
When motors are connected in parallel, par. 1-02
Motor Feedback Source
Motor Control Principle
par. 1-01
motor characteristics (U/f)
® is a registered Danfoss trademark
FC 300 Design Guide
Motor Thermal
Flux
cannot be used, and
Special
must be set to
.