r
c..
“F
f
c
b..
c
L-
C
--
c
c.
6.
LOADING
AND
INSTALLATION
/MELSEC-A
(4)
Power consumption of input circuits (with
an
average number
Win
=
lin
X
E
X
average number of inputs on at one time (W)
Where, lin
=
input current (effective value for AC) (A)
E
=
input voltage (actual operating voltage)
(VI
of
points switched on)
(5)
Power consumption of the special function unit power supply
is expressed as:
WS=IZN
X
24
i-
lrmv
X
100
(W)
The sum of the above values is the power consumption of the
entire
PC
system.
w
wpw
+
w24V
+
WOUT
+
WIN
+
ws
(w)
Further calculations are necessary to work out the power dissi-
pated by the other equipment in the panel.
Generally temperature rise in the panel is expressed
as:
W
T=-
UA
(‘C)
where,
W
=
power consumption of the entire PC system (obtained
as
above)
A =panel inside surface area
(m2)
U
=
6
if the panel temperature is controlled by a fan, etc.
4
if panel air is not circulated.
POINT
I
Fans, heat exchangers
or
cooling units must be installed if
the panel temperature
is
likely to exceed
55’C.
Fans should
be
fied
with suitable filters and guards.
c
c
c
c
P
L-
6-3
IB
lNAl
66238A
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