Motor Thermal Protection - Danfoss VLT AutomationDrive FC 300 Instruction Manual

3. How to Install
3.7.2. Parallel Connection of Motors
The adjustable frequency drive can control
several parallel-connected motors. The total
current consumption of the motors must not
exceed the rated output current I
adjustable frequency drive.
3
Problems may arise at start and at low RPM values if motor sizes are widely different because
small motors' relatively high ohmic resistance in the stator calls for a higher voltage at start and
at low RPM values.

3.7.3. Motor Thermal Protection

The electronic thermal relay in the adjustable frequency drive has received UL approval for single
motor protection when par. 1-90
current, I
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
44
for the
M,N
NOTE
Installation with cables connec-
ted in a common joint, as in the
illustration below, is only recom-
mended for short cable lengths.
NOTE
When motors are connected in
Automatic
parallel, par. 1-29
Motor Adaptation (AMA) cannot
be used.
NOTE
The electronic thermal relay
(ETR) of the adjustable frequen-
cy drive cannot be used for mo-
tor protection for the individual
motor of systems with parallel-
connected motors. Provide fur-
ther motor protection with, for
example, thermistors in each
motor or individual thermal re-
lays (circuit breakers are not
suitable for protection).
Motor Thermal Protection
is set to the rated motor current (see motor nameplate).
M,N
Design Guide
MG.33.A9.22 - VLT is a registered Danfoss trademark
®
VLT AutomationDrive FC 300 Instruction
is set for ETR Trip
for further information.
Manual
and par. 1-24 Motor