Mitsubishi Electric C Series Handling And Maintenance page 84

(4) Operation by surge
To surge by secondary transfer of inductive light-
ening of wires, non-operation test by lightening
impulse is set forth in JIS C-8371, and surge re-
sistivity is ensured. Circuit of the lightening im-
pulse non-operation test is shown at right.
Almost all NVs of Mitsubishi are provided with a
DPDC surge discrimination circuit for judging leak
current to ground by ground fault current and
surge so as to improve unnecessary operation
preventing function.
(5) Operation by loop circuit (circulation current)
In the parallel circuits connected at load side,
diverted current of each phase isn't necessarily
equal between the right and the left branches. If
A phase is diverted into 11A and 9A, for example,
the difference of 1A is to be circulating in the
loop.
Parallel use of two ELCBs is therefore prohibi-
tive as the circulation current causes operation
of the earth leakage circuit breaker.
(5) Operation by induction
Those with loop circuits are susceptible to induc-
tion. Taking a loop as a loop antenna, the pri-
mary winding of ZCT is to be connected with the
antenna, and induction is easily generated.
When a common earth wire is used, place the
ZCT at the position of the continuous line in the
drawing, then the primary conductor of the ZCT
forms a loop. To avoid this, the ZCT must be
placed at the position shown by the dotted line
in the drawing.
Induction can also be generated in the input cir-
cuit of the earth leakage relay, and it is neces-
sary to braid the lead wires between the earth
leakage relay, and the ZCT.
7kV
ELCB
1.2×50µS
Lightening impulse
voltage generator
Test circuit of lightening impulse non-operation
ELCB
11A 10A
Parallel circuits
ZCT
ZCT
Common earth wire
Ground fault detection by earth wire
U
V
C
W
C : 0.03µF R : 0.1MΩ
A B
ELCB
1A
9A 10A
Load
20A
M
Steel
base
R
82