Electrical installation
86
───
Version: 2.2
XTS
8.3
Earthing of the supply
No fuses exist
The figure below is for illustration purposes only. No necessary
fuses exist or are pictured in the simplified illustration.
P
o
w
e
r
S
u
p
p
ly
2
4
V
48V
GND
24V
EtherCAT
cable
P
o
w
e
r
S
u
p
p
ly
4
8
V
C
o
n
tr
o
l
c
a
b
in
e
t
e
a
rt
h
3
3
3
4
4
1
1
2
2
2
4
4
4
3
3
1
1
1
2
2
2
2
2
2
2
1
1
1
4
4
4
4
4
4
3
3
3
3
3
3
3
3
3
3
3
4
4
3
3
3
4
4
1
1
1
2
1
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2
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1
2
1
2
2
1
1
2
8.3.1
Control circuit
The EN60204-1 standard, clause 9.4.3.1. Earth leakages stipulates
that 24 V
DC
control circuits must be earthed. The earthing prevents
the automatic start-up of a machine in the case of a cross-circuit.
U
U
R 24 V
R 48 V
I 48V
I 48V
I 24V
I 24V
I compensation = 0 A
U 48 V
U 24 V
0,75 mm
2
0,75 mm
2
2,5 mm
2
2,5 mm
2
Modules
Supply line 3 x 2,5 mm / 2 x 0,75 mm
2
2
2,5 mm
2
Power supplies
8.3.2
Load current circuit
Beckhoff recommends not to earth the 48 V power supply unit
on the secondary side
The 24 V
DC
return line (0.75 mm
2
) could be overloaded.
If the 48 V power supply unit is earthed, the currents will be distrib-
uted to the 48 V
DC
and 24 V
DC
back wires in accordance with the im-
pedances. Equalizing currents will then flow via the earth on the
power supply unit, as a result of which the 24 V
DC
return line
(0.75 mm
2
) could be overloaded.
U
U
R 24 V
R 48 V
(I 24 V + I 48 V) / 2
I 48 V
(I 24 V + I 48 V) / 2
I 24 V
I compensation =
(I 24 V + I 48 V) / 2
U 48 V
U 24 V
0,75 mm
2
0,75 mm
2
2,5 mm
2
2,5 mm
2
2,5 mm
2
Modules
Supply line 3 x 2,5 mm / 2 x 0,75 mm
Power supplies
I compensation =
(I 24 V + I 48 V) / 2
2
2
