Rockwell Automation AK DBU - Dynamic Braking Unit 600/690 VAC - Manual (Page 15)

Installation/Wiring 1-3
National and local industrial safety regulations and/or electrical codes
may determine additional requirements for these installations.
In case of a failed DBU (IGBT short circuit or a constantly ON
command), the rectified AC line voltage is passed to the brake resistor.
Since the IGBT in the DBU is not switching and therefore its
temperature is not increasing, this fault will not be detected by the
temperature sensor located on the heat sink of the DBU.
To prevent possible damages due to the overloading of the brake
resistors, leads and input rectifier, the installation of a thermal switch on
the brake resistor heat sink is recommended:
The contact of the thermal switch on the brake resistor should be wired
in series with the thermal switch on the DBU to the drives main
contactor control circuit. Refer to
Figure 1.5 .
Fuses
!
ATTENTION: The DBU does not provide DC Bus branch short
circuit protection. Specifications for the recommended fuse to provide
protection against short circuits are provided in
Appendix A .
Protection of Brake Resistors and Conductors