5
●
Grounding Method and Precautions
(1) Principles of One-point Grounding
It would be best to consider that it is grounding that "determines electrical
potential". Do not use common return circuits to return currents for
grounding. Under normal conditions, do not send current through
grounding lines (Do not use common return circuits to return currents for
grounding.).
(2) As much as possible use independent ground (keep grounding
pole at least 10m away from other grounding poles).
1
Use Ground to 100 W or less, and use independent ground which is
separated from the grounding of other devices
(See Figure 12 (a))
2
If using an independent ground is not possible, then use a common
ground as shown in
Figure 12 (b)
. Connect to the ground pole of the
other device.
3
Never connect to the same ground as a device that draws a large
amount of power, such as a motor or inverter. Ground the devices
separately to avoid mutually adverse influences.
4
To prevent electrical shock, do not connect to ground poles
(especially steel frames) to which multiple devices are connected.
5
As much as possible keep the grounding pole close to the PLC, and
keep the grounding line short.
(3) Grounding Precautions
1
If the same ground is used for both the signal lines and the
enclosure, isolate the channel base (a grounded metal plate inside
a control panel) with an insulating material.
(See Figure 13)
2
The panel which contains the PLC must be insulated from other
electrical devices. This is to prevent the effect of the leakage of
current from other electrical devices.
3
When there is high fre
q
uency e
q
uipment nearby, please be sure
that the panel which holds the PLC is grounded, in addition to the
high fre
q
uency e
q
uipment.
4
When grounding the shield conductor in the event of shielded cable
used in the wiring of input and output, connect the shield near the
PLC to the enclosure ground terminal, as shown in
Figure 14
. For
communication cables, please be sure to maintain shield
processing in the communications unit manual.
(4) PLC Protective Ground Terminal
The PLC contains the following two ground terminals.
: Protective ground terminal that is always connected to the PLC
chassis for the prevention of electric shock.
: Functional ground terminal: Connected to a neutral point in the
noise filter to provide a ground when power supply noise
causes malfunctioning.
When properly grounded, the terminals will serve to reduce
common mode noise from the power supply, but sometimes the
grounding can result in picking up more noise, so care should be
taken when using the terminals.
(5) Grounding for AC Power Supply Units When wiring to
an AC Power Supply Unit. If one power supply phase
of the equipment is grounded, always connect the
grounded phase to the L2/N (or L1/N) terminal.
PLC
Other Device
s
le
ss
th
a
n 100 W
PLC
Other Device
s
PLC
Other Device
s
(
a
) Excl
us
ive Gro
u
nding....
Preferred
(
b
) Common gro
u
nding....
Accept
ab
le
(c) Common gro
u
nding....
Incorrect
Fig
u
re 12. Gro
u
nding Method
s
Fig
u
re 1
3
. Ex
a
mple: In
su
l
a
ting
a
nd Gro
u
nding
a
n Enclo
su
re
Excl
us
ive
Gro
u
nding
I
s
ol
a
tor
Common B
as
e
C
S
/CJ-
s
erie
s
PLC
s
h
a
ve
a
n
i
s
ol
a
ted (flo
a
ting) mo
u
nting
s
tr
u
ct
u
re to m
a
ke it more
diffic
u
lt to
b
e
a
ffected
b
y
noi
s
e from the in
s
t
a
ll
a
tion
condition
s
su
ch
as
a
control
p
a
nel.
Fig
u
re 14.
S
hield C
ab
le Gro
u
nding
PLC
O
u
tp
u
t
Common
Inp
u
t
Common
Di
a
gr
a
m 15. PLC Gro
u
nding Termin
a
l
AC
S
ide
PLC
S
ide
L1
L2/N
Bibliography
1
Programable Controller Maintenance/Inspection Handbook May 2002 NECA
2
SYSMAC CS Series User Manual Setup Edition
