236 Resistor brakingA thermal switch (standard in ABB resistors) is required for safety reasons. The thermalswitch cable must be shielded and may not be longer than the resistor cable. Wire theswitch to a digital input on the drive control unit as shown in the figure below. Protecting the resistor cable against short-circuitsThe input fuses will also protect the resistor cable when it is identical with the input cable.Mechanical installation of external brake resistorsAll brake resistors must be installed outside the drive. Obey the resistor manufacturer’sinstructions.Electrical installation Checking the insulation of the assemblyObey the instructions given in section Brake resistor and resistor cable on page 99. Connection diagramSee section Power cable connection diagram example (6-pulse) on page 105. Connection procedure• Connect the resistor cables to the R+ and R- terminals in the same way as the otherpower cables. If a shielded three-conductor cable is used, cut the third conductor andground the twisted shield of the cable (protective earth conductor of the resistorassembly) at both ends• Connect the thermal switch of the brake resistor as described in section Protecting thesystem against thermal overload on page 235.Start-upSet the following parameters (ACS880 primary control program):• Disable the overvoltage control of the drive by parameter 30.30 Overvoltage control.• Set parameter 31.01 External event 1 source to point to the digital input where thethermal switch of the brake resistor is wired.• Set parameter 31.02 External event 1 type to Fault.• Enable the brake chopper by parameter 43.06 Brake chopper enable. If Enabledwith thermal model is selected, set also the brake resistor overload protectionparameters 43.08 and 43.09 according to the application.• Check the resistance value of parameter 43.10 Brake resistance.With these parameter settings, the drive stops by coasting at brake resistorovertemperature. For settings of other control programs, see the appropriate firmwaremanual.Θ +24VD xDIx x
