Hardware Manual

244 Resistor braking
Note: If the E
R
value is not sufficient, it is possible to use a four-resistor assembly in
which two standard resistors are connected in parallel, two in series. The E
R
value of
the four-resistor assembly is four times the value specified for the standard resistor.
 Selecting a custom resistor
If you use a resistor other than the default resistor, make sure that:
1. The resistance of the custom resistor is greater or equal than the resistance of the
default resistor in the rating table on page 249:
where
2. The load capacity of the custom resistor is higher than the instantaneous
maximum power consumption of the resistor when it is connected to the drive DC
link voltage by the chopper:
where
 Selecting and routing the brake resistor cables
Use the same cable type for the resistor cabling as for the drive input cabling to
ensure that the input fuses also protect the resistor cable. Alternatively, a two
conductor shielded cable with the same cross-sectional area can be used.
R Resistance of the custom resistor.
WARNING! Never use a brake resistor with a resistance smaller than
R
min
. The drive and the chopper are not able to handle the overcurrent
caused by the low resistance.
R
min
Resistance of the default resistor
P
r
Load capacity of the custom resistor
U
DC
Drive DC link voltage.
1.35 · 1.25 · 415 V DC (when supply voltage is 380 to 415 V AC)
1.35 · 1.25 · 500 V DC (when supply voltage is 440 to 500 V AC) or
1.35 · 1.25 · 690 V DC (when supply voltage is 525 to 690 AC)
R Resistance of the custom resistor
R > R
min
P
r
<
U
DC
R
2