2 Assembly and installation
BU 0600 en-2319 27
2.2 Braking resistor (BR)
Hot surfaces
The braking resistor and all other metal components can heat up to temperatures above 70 °C.
• Danger of injury due to local burns on contact.
• Heat damage to adjacent objects.
Allow sufficient cooling time before starting work on the product. Check surface temperature with
suitable measuring equipment. Maintain an adequate distance to adjacent components or provide
protection against contact.
To protect the braking resistor against overload, the electrical data of the braking resistor which is
used must be parameterised in parameters P555, P556 and P557.
During dynamic braking (frequency reduction) of a three-phase motor, electrical energy is returned to
the inverter. An external brake resistor can be used in order to prevent the FI from being shut down
due to overvoltage. With this, the integrated brake chopper (electronic switch) pulses the intermediate
circuit voltage (switching wave approx. 420 V / 775 V (/825 V) DC, according to the mains voltage)
(115 V, 230 V/400 V(/500 V)) to the brake resistor. Here the excess energy is converted into heat.
For inverter powers up to 7.5 kW (230 V: up to 4,0 kW) a standard bottom-mounted resistor
(SK BRU5-..., IP40) can be used. Approval: UL, cUL
SK BRU5-…
Figure 2: Frequency inverter with bottom-mounted braking resistor SK BRU5-...
For frequency inverters above 3 kW chassis-mounted resistors (SK BR2-..., IP20) are also available.
These must be mounted in the control cabinet, close to the frequency inverter. Approval: UL, cUL
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