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11. OPTIONS AND PERIPHERAL EQUIPMENT
11 - 43
11.11 Earth-leakage current breaker
(1) Selection method
High-frequency chopper currents controlled by pulse width modulation flow in the AC servo circuits.
Leakage currents containing harmonic contents are larger than those of the motor which is run with a
commercial power supply.
Select an earth-leakage current breaker according to the following formula, and ground the servo
amplifier, servo motor, etc. securely.
To minimize leakage currents, make the input and output cables as short as possible, and make the
grounding cable longer than 30 cm.
Rated sensitivity current ≥ 10 • {Ig1 + Ign + Iga + K • (Ig2 + Igm)} [mA] ···································· (11.1)
Ign
Noise filter
Cable
Ig1 Iga Ig2 Igm
M
Servo
amplifier
NV
Cable
Earth-leakage current breaker
K
Type
Mitsubishi
products
Models provided with
harmonic and surge
reduction techniques
NV-SP
NV-SW
NV-CP
NV-CW
NV-HW
1
General models
BV-C1
NFB
NV-L
3
Ig1: Leakage current on the electric channel from the earth-leakage current breaker to the input
terminals of the servo amplifier (Found from Fig. 11.2.)
Ig2: Leakage current on the electric channel from the output terminals of the servo amplifier to the servo
motor (Found from Fig. 11.2.)
Ign: Leakage current when a filter is connected to the input side (4.4 mA per one FR-BIF)
Iga: Leakage current of the servo amplifier (Found from table 11.3.)
Igm: Leakage current of the servo motor (Found from table 11.2.)
Leakage current [mA]
Cable size [mm
2
]
120
100
80
60
40
20
0
2 5.5 14
3.5 8
38100
22
30
60150
80
Fig. 11.2 Example of leakage current per km (lg1, lg2) for CV cable run in metal conduit