Note: ABB has not verified that the EMC requirements are fulfilled with external
user-defined brake resistors and cabling. The EMC compliance of the complete
installation must be considered by the customer.
Maximum cable length
The maximum length of the resistor cable(s) is 10 m (33 ft).
Placing the brake resistor
Install the resistors outside the drive in a place where they will cool.
Arrange the cooling of the resistor in a way that:
• no danger of overheating is caused to the resistor or nearby materials
• the temperature of the room the resistor is located in does not exceed the allowed
maximum.
Supply the resistor with cooling air/water 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 in brake circuit fault situations
Protecting the system in cable and brake resistor short-circuit situations
The drive input fuses will also protect the resistor cable when it is identical with the input
power cable.
Protecting the system against thermal overload
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.
Resistor braking 341
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