Danfoss VT2800 Series Design Manual page 27

Protective functions during installation
When a brake resistor is installed, the best
possible endeavors should be made to avoid
overloads, as the heat generating from a brake
resistor may involve a fire risk.
NB!:
The brake resistor should be fitted to a
nonflammable material.
For protection of the installation, a thermal relay
should be fitted that cuts off the frequency converter
if the brake current becomes too high. Flat
pack resistors are self-protecting.
Some of the Danfoss Brakeresistors contain a thermal
switch (see table further on). This switch is NC
(normally closed) and can be used e.g. coasting stop
reverse between terminal 12 and 27. The dri v e will
then coast, if the thermal switch is opened.
NB!:
The thermal switch is not a protecti v e
device. For protection, use a thermal
switch as shown in the figure.
MG.28.E9.02 - VLT is a registered Danfoss trademark
®
VLT 2800 Series
Calculate the brake current setting of the
thermal relay as follows:
Itherm relay =
R is the current brake resistor value calculated in
br
the section on "Calculation of brake resistance". The
figure shows an installation with a thermal relay.
The brake current setting of thermal relay for Danfoss
40% brakeresistors can be found in the table further on.
27