INSTALLATION AND WIRING
41
(2) Selecting the rated sensitivity current for the earth leakage circuit
breaker
When using the earth leakage circuit breaker with the inverter circuit, select its rated
sensitivity current as follows, independently of the PWM carrier frequency:
Leakage current example of 3-phase
induction motor during commercial
power supply operation (200V 60Hz)
Cable size (mm
2
)
55
0.1
1.5
3.7
2.2
7.5
15 22
11
37
30 45
0.2
0.3
0.5
0.7
1.0
2.0
5.5
18.5
Leak
a
ge c
u
rr
en
t(
mA)
Motor capacity (kW)
Example of leakage current per 1km in
cable path during commercial power
supply operation when the CV cable is
routed in metal conduit
(200V 60Hz)
0
20
40
60
80
100
120
3.5
5.5
8
22
30
38
60
80
100
150
Leak
a
ge c
u
rr
en
t(
mA)
2
14
!
Progressive Super Series (Type SP, CF, SF, CP)
Rated sensitivity current: I
∆
n
≥
10
×
(lg1+Ign+lg2+lgm)
!
Conventional NV series (Type CA, CS, SS produced prior to '91)
Rated sensitivity current: I
∆
n
≥
10
×
{lg1+lgn+3
×
(lg2+lgm)}
lg1, lg2 : Leakage currents of cable path during commercial power supply operation
lgn*
: Leakage current of noise filter on inverter input side
lgm
: Leakage current of motor during commercial power supply operation
<Example>
Ig1 Ign
Ig2
Igm
5.5mm
2
×
5m 5.5mm
2
×
70m
IM
3
φ
200V 2.2kW
Inverter
NV Noise filter
Note: 1. The earth leakage circuit breaker should be installed to the primary (power
supply) side of the inverter.
2. Ground fault in the secondary side of the inverter can be detected at the
running frequency of 120Hz or lower.
3. In the connection neutral point grounded system, the sensitivity current
becomes worse for ground faults in the inverter secondary side. Hence, the
protective grounding of the load equipment should be 10
Ω
or less.
4. When the breaker is installed in the secondary side of the inverter, it may be
unnecessarily operated by harmonics if the effective value is less than the
rating. In this case, do not install the breaker since the eddy current and
hysteresis loss increase and the temperature rises.
*
Note the leakage current value of the noise filter installed on the inverter input
side.
