￭
Placing the brake resistors
Install the resistor assembly outside the drive in a place where it is able to cool
effectively.
Arrange the cooling of the resistor so that:
• no danger of overheating is caused to the resistor or nearby materials, and
• 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.
￭
Protecting the system against thermal overload
The brake chopper protects itself and the resistor cables against thermal overload
when the cables are dimensioned according to the nominal current of the drive.
The drive control program includes a resistor and resistor cable thermal protection
function which can be tuned by the user. See the firmware manual.
ABB requires that the resistor has a thermal switch (standard in ABB resistors)
which is wired to the chopper for safety reasons. The thermal switch cable must
be shielded and may not be longer than the resistor cable.
￭
Protecting the system in fault situations
The drive has a brake thermal model which protects the brake resistor against
overload. ABB recommends to enable the thermal model at start up.
ABB recommends to equip the drive with a main contactor for safety reasons even
when you have enabled the resistor thermal model. Wire the contactor so that it
opens in case the resistor overheats. This is essential for safety since the drive
will not otherwise be able to interrupt the main supply if the chopper remains
conductive in a fault situation. An example wiring diagram is shown below. ABB
recommends that you use resistors equipped with a thermal switch (1) inside the
resistor assembly. The switch indicates overtemperature.
246 Resistor braking
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