Motor Cables; Motor Thermal Protection; Brake Connection; Earth Connection - Danfoss VLT 2800 Manual

the stator calls for a higher voltage at the start and at
low rpm values.
In SYSTEMs with motors connected in parallel, the
electronic thermal relay (ETR) of the frequency con-
verter cannot be used as motor protection for the
individual motor. For this reason further motor protec-
tion must be used, e.g. thermistors in each motor or an
individual thermal relay. (Circuit breakers are not suit-
able as protection).
NB!
Parameter 107 Automatic motor adaption,
AMT cannot be used when motors are
connected in parallel. Parameter 101 Tor-
que characteristic must be set to Special
motor characteristics [8] when motors are
connected in parallel.

Motor cables

See Technical data for correct dimensioning of motor
cable cross-section and length. Always comply with
national and local regulations on cable cross-section.
NB!
If an unscreened/unarmoured cable is
used, some EMC requirements are not
complied with, see EMC test results in the
Design Guide.
If the EMC specifications regarding emission are to be
complied with, the motor cable must be screened/arm-
oured, unless otherwise stated for the RFI filter in
question. It is important to keep the motor cable as
short as possible so as to reduce the noise level and
leakage currents to a minimum. The motor cable
screen must be connected to the metal cabinet of the
frequency converter and to the metal cabinet of the
motor. The screen connections are to be made with
the biggest possible surface area (cable clamp). This
is enabled by different installation devices in different
frequency converters. Mounting with twisted screen
ends (pigtails) is to be avoided, since these spoil the
screening effect at high frequencies. If it is necessary
to break the screen to install a motor isolator or motor
relay, the screen must be continued at the lowest pos-
sible HF impedance.

Motor thermal protection

The electronic thermal relay in UL-approved frequency
converters has received the UL-approval for single
motor protection, when parameter 128 Motor thermal
MG.27.E2.02 - VLT is a registered Danfoss trademark
protection has been set for ETR Trip and parameter
105 Motor current, I has been programmed to the
M, N
rated motor current (see motor nameplate).

Brake connection

No. 81 82 Brake resistor
R- R+ terminals
The connection cable to the brake resistor must be
screened/armoured. Connect the screen to the metal
cabinet of the frequency converter and to the metal
cabinet of the brake resistor by means of cable clamps.
Dimension the cross-section of the brake cable to
match the brake torque.
See the Design Guide for dimensioning of brake resis-
tors.
NB!
Please note that voltages up to 850 V DC
occur on the terminals.

Earth connection

As leak current to the earth is higher than 3.5 mA, the
frequency converter must always be earthed accord-
ing to prevailing national and local regulations. To
guarantee that the earth cable has a good mechanical
connection to terminal 95, the cable cross section must
2
be at least 10 mm or 2 rated earth wires that are ter-
minated separately. To increase safety you can install
an RCD (Residual Current Device), which guarantees
that the frequency converter trips when leak current
becomes too high. See also RCD Application Note
MN.90.GX.02.
51