Mitsubishi Electric C Series Handling And Maintenance page 86

(12) Operation by carrier phone unit
Malfunctions of the ELCB can result in some cases when attached to a line provided with a carrier
phone, which enables calls through the power line.
Since the carrier phone forcefully gives high frequency signals (normally 50kHz to 400kHz) between
the line and the ground, the ELCB detects the high frequency signals as if they are leak current and
leads to malfunction. Malfunction or not depends largely on magnitude of the high frequency signals,
high frequency characteristic of the ELCB, and degree of rated sensitive current.
(13) Operation by electromagnetic wave
When a portable type transceiver is placed near the ELCB at transmission, particularly intense mag-
netic field is generated easily resulting in malfunction. Generally speaking, frequency bands of por-
table type transceivers are 27/28MHz, 50/50MHz, 150MHz, 400MHz, and 900MHz, and the output is
about 0.5 to 5W. It is confirmed that the ELCB is free from any malfunction when different kinds of
transceivers of 5W output are used for transmission being placed at 1m from the ELCB.
(14) Operation by inverters
Inverters operate many high-frequency components as they turn A.C. power supply to D.C. through
rectification, then turn to A.C. again by switching through transistors.
Increased static capacity to ground sometimes causes malfunctions as the high frequency compo-
nents are kept flowing by the static capacity to ground. To use ELCB in general in an inverter circuit, it
is necessary to select those of lower sensitive current than usual in order avoid unnecessary opera-
tion.
For ground fault detection of high sensitivity in inverter circuit and yet for stable ground fault detection
at both the primary and the secondary sides of the inverters, it is necessary to use an ELCB designed
for higher harmonic earth-leakages and surges, which is hardly affected by high frequency compo-
nents, as the measure against the inverter.
It is also essential to install the ELCB at the primary side of the inverter, and never at the secondary
side.
(15) Others
As electronic arrangement of load equip-
ment advances, surge absorbers are in-
stalled in the equipment more and more to
protect them against surge. As the surge ab-
sorbers connected to the ground discharge
the surge to the ground, a high leak current
is generated to the ground, for a short time
though, and unnecessary operation of the
ELCB is resulted in some cases.
Most Mitsubishi's ELCB are provided with a
DPDC surge discriminating circuit for judg-
ing ground fault current by failure such as faulty insulation from leak current to ground by surge, and
improvement in the performance of preventing unnecessary operation is realized even when the surge
absorber is installed between the line and the ground.
ELCB
1
C1
Applicable circuit to inverter
Circuit and
route of leak
current to
ground
Inverter
1
C2
A load equipment is protected by a surge absorber
Surge
Load
equipment
Gapless surge
absorber
Leak current to ground through surge absorber
IM
Load
equipment
ELCB
I
S
Discherge gap
type absorber
I
S
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