Correct Wiring of Electrically Isolated CAN Networks
7.4 Electrical Grounding
●
For CAN devices with electrical isolation the CAN_GND must be connected between the
CAN devices.
●
CAN_GND should be connected to the earth potential (FE) at
exactly one
point of the
network.
●
Each
CAN interface with electrical connection to earth potential
acts as a grounding point.
For this reason it is recommended not to connect more than one
CAN device with electrical
connection to earth potential.
●
Grounding can be made e.g. at a termination connector (e.g. order no. C.1302.01 or
C.1301.01).
7.5 Bus Length
NOTICE
Please note that the cables, connectors and termination resistors used in CANopen
networks shall meet the requirements defined in ISO11898-2.
In addition, further recommendations of the CiA, like standard values of the cross
section, depending on the cable length, are described in the CiA recommendation
CiA 303-1 (see CiA 303 CANopen Recommendation - Part 1: „Cabling and connector pin
assignment“, Version 1.8.0, Table 2).
Bit-Rate
[kbit/s]
Theoretical values of
reachable wire length
with esd interface
l
max
[m]
CiA recommendations
(07/95) for reachable
wire lengths l
min
[m]
Standard values of
the cross-section
according to
CiA 303-1
[mm²]
1000
37
25
0,25 to 0,34
800
666,6
500
333,3
250
59
80
130
180
270
50
-
100
-
250
0,34 to 0,6
166
125
420
570
-
500
0,5 to 0,6
100
83,3
66,6
50
710
850
1000
1400
650
-
-
1000
0,75 to 0,8
33,3
20
12,5
10
2000
3600
5400
7300
-
2500
-
5000
not defined in
CiA 303-1
Table 7:
Recommended cable lengths at typical bit rates (with esd-CAN interfaces)
●
Optical couplers are delaying the CAN signals. esd modules typically reach a wire length of
37 m at 1 Mbit/s within a proper terminated CAN network without impedance disturbances
like e.g. caused by cable stubs > 0.3 m.
CAN-PCIeMini/402-2(-FD)
Hardware Manual • Doc. No.: C.2044.21/ Rev. 1.1
Page 23 of 30
