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the temperature of the room the resistor is located in does not exceed the allowed
maximum.
Supply the resistor with cooling air or coolant according to the resistor manufacturer's
instructions.
WARNING!
The materials near the brake resistor must be non-flammable. The surface
temperature of the resistor is high. Air flowing from the resistor is of hundreds of
degrees Celsius. If the exhaust vents are connected to a ventilation system, make
sure that the material withstands high temperatures. Protect the resistor against
contact.
Selecting the resistor thermal switch circuit cable
Make sure that the cable in the resistor thermal switch circuit meets the following
requirements:
•
shielded cable
•
rated operating voltage between a core and ground > 750 (U
•
insulation test voltage > 2.5 kV
•
jacket material for at least 90 °C (194 °F). Take into account further requirements due
to resistor construction and temperature.
Protecting the system against thermal overload
The brake control program includes a resistor and resistor cable thermal protection function,
which can be tuned by the user. The brake chopper protects itself and the resistor cables
against thermal overload. Make sure that the resistor assembly is equipped with a thermal
switch, which is connected to chopper control unit input.
For more information on the thermal protection function, see the appropriate firmware
manual.
￭
Operation principle
If the resistor overheats, the thermal switch opens and interrupts the chopper control unit
input signal and the chopper stops operating. In addition, the control unit relay output either
opens the drive main contactor/breaker or gives a fault indication to the overriding control
system, which takes care of the protection.
Protecting the system against short-circuits
Equip the brake unit with brake chopper fuses and brake resistor fuses.
The fuses protect the brake chopper, the brake resistors and the brake circuit cables in a
short-circuit situation.
Guidelines for planning the electrical installation 47
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