7
of the system. Generally not less than 2~4 times of the maximum measured residual current: 4 times
of the branch line; Branch line 2.5 times; Main line 2 times. According to the empirical formula:
Single-phase circuit: I
△
n
≥In/2000 (lighting)
Three-phase loop: I
△
n
≥In/1000 (power or power lighting hybrid) I
△
n
is the maximum current.
4) In order to ensure the selectivity of hierarchical protection action, the current and time
coordination between the upper and lower levels shall conform to the following provisions:
I
△
n1
(upper) ≥I
△
n2
(lower)
tF (upper ASJ return time) > tFA (low ASJ break time), the time difference is not less than 0.2s.
General branch line and end: 30~100mA, ≤0.1s;Branch line: 300~500mA, 0.2~0.8S;
Main line: 500~1000mA, ≤2s.
5
）
System Selection Instructions
Type of
system
Wiring of system
description
TT system
ASJ is recommended. The earth fault
current is very small and difficult to be
estimated, operating current can not be
reached, and the hazardous voltage will
appear on the shell.
TN-S
system
ASJ can be used. cut off the fault more
quickly and sensitively, improve the safety
and reliability. PE line is not allowed to pass
through the transformer.
TN-C
system
ASJ can not be used, if PEN line is not
iterative earthing, the ASJ refuse to operate;
if PEN line is iterative earthing, ASJ will be
misoperated.
TN-C-S
system
If it is the TN-C system in front of the point
F, ASJ is not allowed; if it is the TN-S
system at the back of point F, ASJ can be
used, but PE line cannot pass through the
transformer.
IT system
ASJ can be applied. The insulation
monitoring device is applied firstly and the
residual current device is applied to prevent
the reduction of insulation in the system and
make it the secondary backup protection,
5.5 Instructions for the selection of transformer
type
hole
Main loop rated current
ratio
AKH-0.66L45
45mm
80A
1A:1mA
