Connection Of The Brake Unit (Fr-Bu2); Emc And Leakage Currents - Mitsubishi Electric FR-D720 K Series Instruction Manual

2.4.2

Connection of the brake unit (FR-BU2)

Connect the brake unit (FR-BU2(-H)) as shown below to improve the braking capability at deceleration. If the transistors in the
brake unit should become faulty, the resistor can be unusually hot. To prevent unusual overheat and fire, install a magnetic
contactor on the inverter's input side to configure a circuit so that a current is shut off in case of fault.
(1) Connection example with the GRZG type discharging resistor
Three-phase AC
power supply

Connect the inverter terminals (P/+ and N/-) and brake unit (FR-BU2) terminals so that their terminal names match with each other.
(Incorrect connection will damage the inverter and brake unit.)

When the power supply is 400V class, install a step-down transformer.

The wiring distance between the inverter, brake unit (FR-BU2) and discharging resistor should be within 5m.
Even when the wiring is twisted, the cable length must not exceed 10m.

It is recommended to install an external thermal relay to prevent overheat of discharging resistor.

Refer to FR-BU2 manual for connection method of discharging resistor.
<Recommended external thermal relay>
Brake Unit Discharging Resistor
FR-BU2-1.5K GZG 300W-50 (one)
FR-BU2-3.7K GRZG 200-10 (three in series)
FR-BU2-7.5K GRZG 300-5 (four in series)
FR-BU2-15K GRZG 400-2 (six in series)
FR-BU2-H7.5K GRZG 200-10 (six in series)
FR-BU2-H15K GRZG 300-5 (eight in series)
FR-BU2-H30K GRZG 400-2(twelve in series)
NOTE
 Set "1" in Pr. 0 Brake mode selection of the FR-BU2 to use GRZG type discharging resistor.
 Do not remove the jumper across terminals P/+ and P1 except when connecting a DC reactor (FR-HEL).
MC
MCCB
R/L1
S/L2
T/L3
Inverter
Recommended External
Connection of stand-alone option unit

T
MC
GRZG type
discharging resistor
OCR
Motor
U
External thermal

relay
V IM
W

PR
P/+
P/+

N/-
N/-
BUE
SD

10m or less
Thermal Relay
TH-T25-1.3A
TH-T25-3.6A
TH-T25-6.6A
TH-T25-11A
TH-T25-3.6A
TH-T25-6.6A
TH-T25-11A
ON OFF OCR contact
MC

R R
FR-BU2
A
B

C
1/L 5/L
1 3
2/T 6/T
1 3
To the brake unit To a resistor
terminal P/+
2
33